text:
\section{Introduction}
More than a year and half  ago the `Large Hadron Collider' (LHC), came into
limelight, due to the spectacular show of its start up, the equally spectacular
accident soon after and also for the doomsday stories that circulated around
its start up.
The accident  put it out of action for a while. Now the necessary repairs done, the damaged pieces replaced, the machine has taken the first tentative steps
in its life beginning on November 23, 2009. Having set a world record for the
proton beam energy, of 1180 GeV, on November 30, 2009, it went back to the
lower beam energy of $450$ GeV per beam  and ran for about two weeks in the
collision mode. The detectors collected data, corresponding
to a few hundred thousand $pp$ collision events,\footnote{At full throttle
LHC detectors will have to deal with over 600 million proton collisions
per second.} over this period
confirming  that their intricate machinery performed as it should and can
measure the properties of the myriad of particles produced in these collisions,
to the desired accuracy.  After a winter shut down (partially caused  by the
escalation in energy costs due to the increased energy demands otherwise
in winter) the  machine started working again on 20 th February 2010.
After circulating proton beams at the higher energy of 3.5 TeV since 19th
March 2010, finally  collisions at the total centre of mass energy of
7 TeV happened  on the 30th  March 2010;  albeit this was still only
half the originally planned  energy and with 10 times less number
of particles per bunch than initially foreseen for the restart.  The decision
to do so being taken, in the words of CERN Director General, Rolf Heuer, as a
`prudent step by step approach' as `the LHC is not a turnkey project'. Papers,
presenting results from the December runs have already been published in
research journals~\cite{:2009dt,Khachatryan:2010xs,Aad:2010rd} and more have
been submitted already from the collisions in March~\cite{Khachatryan:2010us},
with thousands of authors signing them. Particle physicists: experimentalists
and theorists alike, are waiting now with baited breath, just as they have
been for more than a decade now, for the results which will come out of these
collisions. I write these lines  from CERN, where even in the cafeteria now
the television screens display information about the LHC machine operation!

While the rest of the world came to know of this extremely complicated
endeavor only about a year and half ago, for the worldwide community of
particle
physicists (which incidentally developed the World Wide Web (WWW) two decades
ago), this is perhaps the concluding chapter of the long running love story
between the world of fundamental constituents of matter and that of the
accelerators which get these particles to move at the speed of light. In this
article I discuss why thousands of particle physicists the world over,
together, have embarked upon this truly mammoth project and worked  on it over
three decades. I wish to highlight what we all hope to learn from doing
experiments with this unique machine. The construction of this accelerator and
that of the equally huge and complex detectors,
by itself, has been an amazing and utterly impressive engineering achievement.
To appreciate the scope of this achievement by accelerator physicists and
engineers, from CERN and  the rest of the world, including India,
we should follow a story which began perhaps a century ago. It is also a story
of a development of a methodology of the ''mega' science projects that the
high energy physicists have developed.

The development of our knowledge of the laws of physics that function at the
heart of the matter has been very closely interlinked with that of the
accelerators. It may be said that the discovery of the first fundamental
particle, the electron, by J.J. Thompson in 1897 was due to the first
`accelerator: a cathode ray tube', which accelerated electrons.  The partnership
between accelerators and particle physicists on this adventure has continued
through the century. The legendary physicist Lord Rutherford,  who discovered
existence of a nucleus inside an atom using the alpha particles emitted by
the radioactive nuclei, had said,  dreaming about high energy particles to
uncover nature's secret ``It has long been my ambition to have
available a copious supply of atoms and electrons which have energies
transcending those of the alpha, beta  particles from the radioactive bodies''.
His dream was full filled by Walton and Cockroft in the Cavendish Laboratory.
The target of energy (MeV : Million electron volt) to which the particles
needed to be accelerated, was set by Gamow's theory of radioactive decay.
This gave the height of Coulomb barrier to $\alpha$ emission in a nucleus
and hence indicated the energy level to which particles need to be accelerated
for possible artificial radioactivity:  the aim of Rutherford's experiments at
that time. Since then the nuclear/particle physicists have been setting the
bar higher and higher and accelerator physicists have been clearing it with
regularity, like Sergey Bubka or Yelena Isinbayeva.

Compared to the early machine by Walton and Cockroft which fitted in a room
or the early cyclotron by Lawrence and Livingstone which was only 11
inches in diameter, today's machines are truly gigantic. Further, the energies
to which these machines accelerate the particles are higher by many orders of
magnitude.  The Tevatron at the Fermi  National Accelerator
Laboratory (FNAL) in Batavia in USA, held the record for accelerating
protons to about a thousand times its rest mass energy $\sim$ 1000 GeV
or 1 TeV, corresponding to a total collision energy of 2000 GeV; a feat that
the LHC eclipsed by first reaching a total collision energy of 2360 GeV and
then 7000 GeV, as said before.

Acceleration of particles to these high energies is not achieved by the
use of electrostatic force alone, but has to be by a judicious combination
of the alternating electric fields and magnetic fields as is done in  the
more sophisticated cyclotron. Lawrence's first model, costing only US \$ 25
in 1931, used 2000 volts of electricity but produced protons with energy
80,000 electron volts. Magnetic fields are not only required to facilitate
this acceleration of particles, but later also to keep them on a tight leash
and steer the beam  around its path as a tight bunch, without allowing them
to spread apart. All this beam optics
requires careful designing of magnetic fields, with very precise spatial
distribution. Thus an accelerator physicist has to deliver a beam of particles
accelerated to speeds close to that of light\footnote{for the case of 1
TeV protons mentioned above $v = 0.9999995 \times c$}, containing a large
number of particles ($\sim 10^{11}$  or more for the LHC at the nominal
design) and with a small transverse size (a few $\mu m$ at the collision
point for the LHC). The beam has to maintain this size while the particles
are transported across the long periphery of the machine ($27 km$ for the
LHC ring), many times ($\sim 10^6$) over. Clearly this whole exercise poses
extreme technological challenges and requires fine engineering.\footnote{Note
that it is not enough to make these beams of particles of high energy. It has
to be accompanied by the construction of equally intricate detectors to `detect'
traces of particles produced in these collisions.}

The decisions about the type of particles which should collide and the
energies to which they should be accelerated, are  guided crucially by our
current theoretical understanding of fundamental particles and the interactions
among them. This interplay of different sub-disciplines in the field of high
energy physics is seen in  the citation of the  1984  Nobel prize for physics
which was shared by the experimental physicist Carlo Rubbia and the
accelerator physicist
Simon Van Der Meer ``for their decisive contributions to the large project,
which led to the discovery of the field particles W and Z, communicators of
weak interaction".  The large project mentioned in the citation was the Super
proton-antiproton Synchrotron: the $S p \bar p S$  which started operation
at  CERN in Geneva, Switzerland in 1983. This project involved converting
the  proton-proton collider which had been commissioned in 1976, into a
proton-antiproton collider. The need to do so was indicated by theorists'
calculations which showed that given the limited energy to which the proton
could be accelerated using the then available technology, the feat of producing
the $W/Z$ bosons in the laboratory, could be achieved only if one collided
protons on {\it antiprotons} and that too in large numbers. This prediction
was made using the then established Glashow-Weinberg-Salam model (put forward
in 1968) which gave a unified description of the electromagnetic and weak
interactions\footnote{The inventors
of this theory called the EW theory, had already been awarded the Nobel prize
in 1979.} and with the knowledge of the momentum fraction of the proton
carried by some of its  constituents, the quarks and the
anti quarks\footnote{Friedman, Kendall and Taylor, who in 1968 performed the
first experiment which gave indication of the quark structure of the proton,
received Nobel prize for physics in 1990.}. Simon Van Der Meer's discovery of `stochastic cooling' made
it possible to produce tightly focused antiproton beams whereas Rubbia's
vision and drive made it possible for the project to be realised.
Already this little discussion tells a lot of things about the current state
of play in high energy physics, including the need for `project' leaders to
take these big projects from conception to realisation and the very high level
of collaboration necessary, not just among the large number of experimentalists
working together on one single experiment, not just among them and the
theorists, but also among these two groups and the accelerator physicists. The
particle physics community has been grappling for decades and with reasonable
success, with running these mammoth collaborative projects and at the same time
keep individuality, the basis of all progress, alive!

In this narration, I will first try to explain why LHC: the machine and the
experiments with it, are a watershed for particle physics. I will then sketch
the essential link between the development of particle accelerators and that
in our knowledge of the laws governing the interactions among the fundamental
particles, showing how  this journey has reached destination LHC. After this I
briefly describe how the high energy physics experiments of past few decades
have provided important pointers to the physicists who are hunting for the
Higgs boson and other new particles/physics at the LHC. This discussion will
then help us understand  how the decisions for the LHC design; the energy and
number of particles in the beam, were arrived at. I will then end by telling
about the LHC physics agenda and the time line in which the particle physicists
hope to achieve it.

\section{The story of LHC}
\subsection{LHC: a watershed experiment}

As we go along we will try to understand, why particle physicists believe that,
at least one, as yet undiscovered particle, must exist out there and the LHC
will see it. Independent of whether this turns out to be the Higgs boson with
the properties predicted by the corresponding theory, we also expect existence
of even more particles/interactions which LHC will be  in a good position to
find should they exist.
One thing is for sure.  LHC : the machine and the experiment, is going to be
a watershed for the subject of  fundamental particle physics. Particle
Physics will never be the same, independent of what the experiments find.
LHC is now the doorstep and the day of reckoning at hand. We expect the
LHC to find the last missing piece of the standard model, the Higgs boson.
We expect much more. We believe LHC will also point the way ahead (or even to
a dead end?), help  unravel the deepest secrets of nature and space time.
Hence  it is a watershed experiment.

To appreciate why this is so,
it is important to understand the current state of play in the subject.
The normal course through which science progresses is well known to all of us.
Barring the work of geniuses like Einstein, normally, existing theory
and observed phenomena which are unexplained in the framework of that
theory, lead to new theoretical developments. This then leads to
predictions, which then get tested in experiments. However, in the subject
of High Energy Physics (HEP) one is in a very strange situation. We have a
theory, called Standard Model (SM) of particle physics, which works so well
that there seems to be almost no unexplained phenomena.(See Box-I, for some
details of the SM.) Various new theoretical developments have taken place
only by the demands made by the community on the properties that the
mathematical theory aught to have for it to be a
satisfactory description of the fundamental interactions. One example of a very
simple demand is called unitarity: which very simplistically stated means
that probabilities for different events are  bounded by unity, as they always
must be. Some of the theoretical developments beyond the SM (BSM) have also
come by demanding that some features, such as the values of the masses that
different particles have, should be understood from first principles in the
theory. For example, in the SM, we have such a first principle understanding
why the rest mass of the photon is zero. All the efforts to find {\it direct}
proof for any of these new ideas (Supersymmetry, additional compact dimensions
of space\cite{bsm} to name a few), in the various particle physics
experiments and/or to look for their implications in cosmology/astrophysical
situations, have yielded, so far, negative results.
In other words, we seem to have found a `perfect' theoretical description
of fundamental constituents of all the matter and interactions among them,
barring a `direct' verification of one last `piece' of the puzzle, the Higgs
boson.

On the one hand, the particle physics community has  strong theoretical
reasons that there is new physics at the TeV scale, while on the other, the
experimental evidence for its `need' is only in the form of tantalising
`indications' such as  non-zero masses for the neutrinos, or the
dark-matter in the Universe etc. It should be emphasized here, that the
track record of particle physicists is pretty good so far in this context and
theoretical developments based on demands of  aesthetics  alone have been
fruitful at getting at the root of some of the very fundamental questions
about laws of nature. But, admittedly, the time gap between theory and
experiment has never been so big as it is at present. We are still awaiting
the final experimental verification of a theoretical advancement made in 1964.

One direction in which progress can come is
by increasing the available energy at which particle interactions are studied.
There are solid reasons to believe that experiments at an energy  of the
order of a few Terra electron volts (TeV) would bring further progress.
The HEP community expects the three TeV colliders (the $p \bar p$ Tevatron
in USA, the $pp$ collider LHC which has started its journey now and the
International Linear electron-positron Collider (ILC) which is now under
planning) to help us see the way ahead. Due to the higher energy of the LHC
than the Tevatron, at present all the particle physicists look to the LHC to
provide the final clinching evidence for the SM and give at least a glimpse
of the physics beyond the SM (BSM), which all of them  believe, must exist at
around the TeV scale.

\subsection{Cosmic Connections}
Very interestingly the fundamental laws of particle interactions operating at
the `heart of the matter' at `'femto' meter scales (or smaller) that the particle
physicists have been studying, have implications for issues
cosmological in nature, concerning the universe, as it was at the
beginning and what it is now. The formation of protons/neutrons in the early
Universe (Nucleosynthesis), the observed abundances of various elements such
as $He,Li$ etc. in the Universe, can now be understood in terms of known
physics of these interactions
and experiments performed in terrestrial environment and laboratories.
However, it is clear now that there are some very basic features of our
universe that seem to indicate existence of particles outside the list
given in the Tables 1 and 2 of Box-I. Among these are the following
facts:
1) The fundamental particles listed in the Tables 1,2  of Box-I constitute only
$4 \%$ of the total visible matter in the Universe and $23 \%$ of the matter in
the Universe that is is `invisible'(so called Dark Matter,DM) does not consist
of particles of the SM, 2)Among the particle content of the Universe, we see
only matter particles and virtually no antimatter particles. To be precise the
difference between the number of baryons and anti-baryons normalised to the
total number of photons, $\frac{N_B - N{\bar B}}{N_\gamma} \sim 10^{-7}$,
\comment{\footnote{If that were not the case, we would have seen results
of annihilation of matter-antimatter, happening in the universe.}}
and 3)The universe seems to be continuously accelerating. The source of this
acceleration is again not found among the known matter/interactions and seems
to indicate an unknown form of `energy' (hence called 'dark energy') which
forms about $73 \%$ of the total mass/energy content of the Universe. All
these indicate very clearly existence of physics beyond what is in the SM.

What is even more interesting is that possible candidates which can throw light
and/or provide solution to these issues, also exist very `naturally' in almost
all the ideas of BSM physics that particle physicists have putting forward
forward for an entirely different reason, viz., to remove some of the
theoretical shortcomings of the currently accepted description of the SM.
But no one idea separates itself completely from the crowd. Experiments
are the ultimate Jury which would choose between these different ideas. At the
LHC, in addition to hunting for the Higgs boson, the last piece of the SM
puzzle, it may be possible to create some of the particles which make up
about $23 \%$ of the total matter in the universe, the dark matter that is
`invisible' to light; or probe the physics that makes the universe of today
contain much more  `matter' than anti-matter.
The LHC can probe this synergy between the world at the femtoscale and
the physics of the entire universe and provide answers to some very basic
question about nature of things! This should clearly show that the `stakes'
in these collider experiments are really high!!

\subsection{Accelerators \& particle colliders: journey unto LHC}
To understand the unique role particle physicists expect the LHC to play,
it is a good idea to briefly look into the history of particle accelerators
These high energy particle accelerators are like microscopes which have
allowed us to peer at the 'heart of matter'.  High energy proton and electron
beams produced using these accelerators have been used in two different modes:
1) The Fixed Target Machines where $e, \mu, \nu$ and $p, \pi$ beams
are incident on a stationary target which consists of light or heavy nuclei.
2) Colliders where beams of accelerated particles collide against each other.
In the latter  class only the $e^+,e^-, p$ and antiproton beams can be
made to collide in enough numbers to make the experiments meaningful.

In case of a fixed target machine, for a beam of energy $E_b$ incident on a
target of mass $M_T$, total energy available for new particle production is
$E_{cm} = \sqrt{M_T E_b}c$, whereas in the collider environment, specialising
to the case where both the beams have particles with same mass and energy, the
energy available for particle production is $2 E_b$. Recall that mass of a
proton, a typical target, is $\sim 1 GeV/c^2$. Thus the collider mode is
superior for new particle production than the fixed target mode, from the point
of view of energetics, as beam energies approach $\sim $ GeV. For example,
a particle called $J/\Psi$ with mass $3.1 GeV/c^2$, now understood to be a
bound state of a charm-quark and an anti-charm quark, was produced for the
first time in 1974 in an $e^+e^-$ collider called SPEAR at SLAC with a
beam energy of $2$ GeV, whereas soon after, the same particle was created in
a fixed target experiment at the Brookhaven National Laboratory which
employed proton beams accelerated to $30$ GeV.

But energy is only one consideration. Equally important are the Luminosity
$\cal{L}$ of collisions, i.e. the number of collisions per unit area, per
unit time and the kind of interactions that the colliding particles possess.
Colliders became a popular tool only after the accelerator physicists developed
better techniques to make intense, well focused beams. In fact the SPEAR
collider mentioned above, was one of the early example of a collider
experiment. Till then the burden of progress was carried mainly by the fixed
target experiments.

Through the early part of these explorations,
experiments with beams of higher and higher energy just revealed constituents
at smaller and smaller distance scales. After the discovery of the  quarks,
in 1968, lying at the heart of protons and neutrons, the later increase in
energy has brought about production of the force carriers and help develop/test
the theory which can describe the interactions among the fundamental
constituents.  Experiments with different  fixed target machines and the
colliders together, provided this information.

The colliders which helped particle physicists in this journey can be
divided in to three different classes based on colliding
particles. The leptonic colliders: 1)electron-positron ($e^+e^-$) and
2) electron-proton ($e^- p$) colliders and the hadronic
colliders: 3)proton-proton($pp$), proton-antiproton ($p\bar p$) ones.

The story began with $e^+e^-$ circular machines in the 60's at Frascati(Italy),
Novosibirsk(Russia) and Orsay(France). It then proceeded through SPEAR (1973),
PEP (1980), SLC(1990) at SLAC, Stanford in USA; DORIS(1973),PETRA(1979) at
DESY, Hamburg in Germany; LEP-I(II)(1989) in CERN, Geneva, Switzerland,
with the  beam energy increasing from a 1.5 GeV at SPEAR to up to (15) 23.4
GeV at  PEP (PETRA), 30 GeV for Tristan, 45 GeV for LEP-I, SLC and 104.5 GeV
for LEP-II. The SLC was the only 'linear' collider among all these.\footnote{
BELLE (KEK: Japan) and BABAR (SLAC: Stanford) are the higher
intensity but lower energy, $E_b \sim 4.5 GeV$ machines, carrying
on the legacy of DORIS at DESY in Germany and CESR at Cornell in USA. This
concerns travel on another front in experimental HEP and not discussed further
here.}
Finally the story
continues now to a possible International Linear Collider (ILC) or Compact
Linear Collider (CLIC). It is not yet clear if and where the last mentioned
colliders will be built but feasibility studies for these two already
go on.

Next colliders to come into play were the proton-proton (pp) and
proton-antiproton ($p \bar p$) machines. The PS (proton synchrotron) built more
than 50 years ago at CERN (and still working today) fed high energy proton beams
to the Intersecting Storage Ring (ISR) : world's first $pp$ collider (1971). The
story then moved on to the Super Proton Synchrotron to achieve $ \bar p p$
collisions at  the  $S p \bar p S$ collider at CERN, in 1983.  Close on its
heels was the Tevatron in USA and now the hadronic machine at the forefront is
the $pp$ machine is the LHC.

Interspersed with these pure leptonic and hadronic colliders, was a machine
which collided  electrons/positrons on  proton. This $ep$ collider HERA in
Hamburg, Germany, provided invaluable information on the quark and gluon
content of the proton, which as we will see below is required to predict
what particles the LHC can produce and at what rate.

A list of some of these different leptonic and hadronic colliders,
of relevance to the discussion here, is presented in the tables~\ref{tab3}
and \ref{tab4}.  Due to the differences in the nature of the hadronic and
leptonic colliders, they have played very complementary roles in our quest
for the fundamental constituents of matter and interactions among them.
\begin{table}
\begin{center}
\begin{tabular}{|c|c|c|c|}
\hline
&&&\\
Period&Type&Energy GeV&Perimeter\\
&&&\\
\hline
1971-1976&pp (ISR) Circular,CERN& $32 \times 32$ & $\sim 7 km$\\
\hline
1983-1985&$p \bar p$ $S p \bar p S$ , Circular,CERN&$270 \times 270$&   "\\
\hline
1987--&$p \bar p$, Circular, Tevatron, USA &{\bf $980 \times 980$}&$\sim 6 km$ \\
\hline
2009&LHC, $p p$,Circular&$1180 \times 1180$ &$\sim 27 km$\\
2010--&CERN&{\bf $3500 \times 3500$} &\\
\hline
\end{tabular}
\end{center}
\caption{List of hadronic colliders of interest, two are still in action.}
\label{tab3}
\end{table}
\begin{table}
\begin{center}
\begin{tabular}{|c|c|c|c|}
\hline
Period&Type&Energy GeV&Perimeter (Circular)\\
&&&Length (Linear)\\
\hline
1973-1983&$e^+ e^-$, Circular&$1.5\times 1.5 $& $\sim 0.6 km$\\
&SPEAR, USA& $3.5 \times 3.5$&\\
\hline
1978-1986&$e^+ e^-$, Circular&$6.0 \times 6.0$&$\sim 2.3 km$\\
&PETRA, Germany&$23.4 \times 23.4$ &\\
\hline
1990-2007&$e^{\pm} p$, Circular&$26.5 \times 800$&$\sim 6.3 km$\\
&HERA, Germany&&\\
\hline
1989-2000&$e^+ e^-$, Circular,CERN& $\sim 45 \times \sim 45$&$\sim 27 km$\\
&LEP-I, LEP-II & $104.5 \times 104.5$&\\
\hline
1989-1999&$e^+ e^-$, Linear& $50 \times 50$ &$\sim 3.2 km$\\
&SLC, USA&&\\
\hline
???&$e^+e^-$,ILC,Linear&$500\times 500$&30 km\\
???& $e^+e^-$, CLIC,Linear&$1500 \times 1500$&$\sim$ 20-40 km\\
\hline
\end{tabular}
\end{center}
\caption{Some of the Leptonic Colliders : past and in planning.}
\label{tab4}
\end{table}
The hadronic and leptonic colliders have different advantages and disadvantages
For $e^+e^-$  colliders the initial beam energy is very accurately known
as the colliding particles are the same ones which are being accelerated.
For the $pp$ or $p \bar p$ machines the colliding particles are
composites and at high energies the colliding fundamental particles
are the (anti-)quarks, gluons: the partons.  From the measurements at HERA
and other fixed target machines, it is known that, on the average only 1/6 th
energy of the proton is available to the colliding partons.  Thus for the same
energy of the beams, $E_{cm} (e^+e^-) \sim   6 E_{cm} (pp)$. Thus to probe
physics at a given energy scale, one needs $pp/p\bar p$ colliders, with higher
energies than the $e^+e^-$ machines. But then it {\it is} easier to accelerate
the $p/\bar p$ to much higher energies. Further for a given beam energies,
these hadronic machines can provide a broad range of energies at which
collisions between partons can happen. Thus a hadronic machine allows us
a broad sweep of energies and one can take a quick/dirty  look at the
landscape, as opposed to an $e^+e^-$ machine where for a fixed beam energy
the collision energy is fixed too! Hence, traditionally the hadronic machines
have been 'discovery' machines and leptonic colliders have been the precision
measurement machines. Further, we really need a hadronic machine to study
processes initiated by strongly interacting particles: quarks and gluons.

The physics flow among these different machines is very interesting. For
example, the studies of $ep$ collisions at the Stanford Linear Accelerator(SLAC)
revealed(1968) that the proton is made up of quarks. Further experiments,
in the next three decades with $\mu p$, $\nu p$ collisions from
Tevatron/CERN and from $ep$ collider HERA, revealed  that the proton contains
 quarks,anti-quarks and gluons (all three collectively called partons);
the evidence for the latter being `indirect'. These experiments further gave
extensive  information on proton momentum fractions carried by the partons.
The $pp$ collider ISR at CERN gave the first evidence of the parton structure
of the proton in $pp$ collisions in 1973.

The experimental evidence for the  first of the heavy quarks and leptons,
the $c$ quark and $\tau$ lepton, happened at the $e^+e^-$ collider SPEAR and
the fixed target experiment at Brookhaven, in 1974-1975. Both, the existence
and the mass of the charm quark was predicted in 1970 based on the EW model of
1964, mentioned earlier. The $\tau$ lepton, discovered at SPEAR, came
uninvited to the party. However, its presence was soon found to be necessary,
from  theoretical considerations, in order to match the pair of quarks whose
presence was predicted from an analysis of the well established phenomenon of
CP violation. The two quarks, so predicted, were bottom/beauty(b) and top(t).
Out of which the bottom was discovered in a fixed target experiment in 1977,
but the discovery of the top quark at the Tevatron had to wait till much later.
The `direct' observation of gluons at the $e^+e^-$ collider
PETRA in Hamburg, Germany in 1978, was then followed by the direct observation
of $W$ and $Z$ at the CERN $p \bar p$ collider in 1983. Their mass had been
predicted while planning this collider, using the results from the experiments
at the lower energy  $e^+e^-$  colliders like PEP/PETRA and TRISTAN along with
those from the fixed target experiments using $\nu$ beams. The first production
of a handful (in two digits) of $W,Z$ at UA-1/UA-2 at CERN in 1983 was then
followed by production of {\it millions} of $Z$ at LEP and SLC in 1990-2000.

This is pattern that is repeated time and again.
The $pp$ or $p \bar p$ machine which is a higher energy, broad band machine
makes discoveries, whereas the cleaner environment of $e^+e^-$ colliders
allows for precision studies. Thus the lepton and hadron colliders have been
alternately taking the  role of leading machine, driving the progress of
particle physics. The precision measurements at LEP-I and LEP-II, having
been  complemented by the hadronic collider Tevatron, which discovered the
last missing quark, the top quark, now time has come for a higher energy broad
band machine.

The information on the main physics discoveries made at different colliders
have been
\begin{figure}
\begin{center}
\includegraphics*[width=12cm,height=9cm]{figs/energy-frontier-small.ps}
\end{center}
\caption{A summary of particle physics discoveries made with different machines}
\label{fig:phys-acc}
\end{figure}
summarised in Fig.~\ref{fig:phys-acc}. This shows how the baton for
discoveries has moved between different machines and how the energy frontier
has moved.
Missing from this figure is the fixed target experiment at SLAC, with electron
beams of energy up to $50$ GeV which made the discovery of light quarks (u,d)
inside proton  in 1968 and the  fixed target machines which followed it at
Fermilab and CERN, with $\mu,\nu$ beams up to energy 800 GeV, which helped
confirm the existence of the strange quark (s).

This shows that the colliders and the fixed target machines have functioned
in tandem, revealing layers of substructure of matter and providing
information which can be used to elucidate the  mathematical description
of interactions  among the fundamental particles. With the LHC, experimental
data using the higher energies reached by the LHC can push knowledge forward,
challenging those who seek confirmation of established knowledge, and those
who dare to dream beyond the paradigm.

\subsection{Precision testing of the SM and pointers to the Higgs hunters}
The most important part of the intellectual achievements in the area of
particle physics over the past five-six decades, arrived at by using the
information from these accelerators and colliders has been the understanding
of the three fundamental interactions (shown in Table 2 of Box-I), in terms of
exchange of the force carriers among the matter particles.
Just like Quantum Mechanics is the correct mathematical framework to describe
the phenomena that occur at short distance scales and/or high energies, the
mathematical framework which can be used to describe and calculate
processes involving creation and annihilation of particles is called Quantum
Field Theory (QFT). In fact the description of all the three interactions,
strong, electromagnetic and weak, in terms of QFT's with special properties,
is the basis of the SM of particle physics. At present a complete
mathematical description of all -- the low energy and high energy-- phenomena
in the world of fundamental particles, is possible in this framework.\footnote{
A lot of these achievements were recognised by a large number of Nobel prizes
in Physics in the past fifty years, beginning with the Nobel prize to Feynman,
Tomanaga and Schwinger in 1960 and ending with the Nobel prize to Y. Nambu,
M. Kobayashi and T. Maskawa in 2008.} To get a feel for the level of precision i
in the experimental measurements and that in the theoretical predictions,
I present in Table~\ref{tab5}, details of some of the most crucial parameters
of the unified theory of electromagnetic and weak interactions (EW theory),
which I have taken from Refs.~\cite{lepewwg,PDG}.
\begin{table}
\begin{center}
\begin{tabular}{|c|c|c|}
\hline
Observable&Experimentally measured value&SM fit\\
\hline
Width of the $Z$ boson: $\Gamma_Z $&$2.4952 \pm 0.0023$ GeV& $2.4959$ GeV \\
\hline
Mass of the $W$ boson: $M_W$ &$80.404 \pm 0.030$  GeV$/c^2$  & $80.376$ GeV$/c^2$ \\
\hline
Mass of the $t$ quark $M_t$ & $172.5 \pm 2.3$ GeV$/c^2$ & $172.9$ GeV$/c^2$\\
\hline
\end{tabular}
\caption{Precision testing of the SM}
\label{tab5}
\end{center}
\end{table}
The level of precision of the EW theory predictions as well as the experimental
measurements and the agreement between the two is quite impressive
\footnote{In fact the almost complete
success of the SM, has led some theorists to wonder whether time has come for
a paradigm shift. Further, a quantum theory of the fourth fundamental
interaction, the gravitation, seems to lie outside the realm of QFT's
describing the three interactions of the SM, the Gauge  Field
theories. String theorists believe that Quantum Field Theories are  sort of a
just a 'low energy' paradigm and string theories might be the language
to  use once you want to include gravitation. Jury is more than out on
this point. It is possible that the LHC might tell us that this belief
of the string theorists is the truth! Then again it may not!}.

However, it has to be said that in order that the theoretical computations
leading to theory predictions in Table~\ref{tab5} can be performed, in addition
to the particles listed in Tables 1,2 of Box-I, one more particle has to exist
in the SM. The so called Higgs boson with spin 0, i.e.a particle
with no spin degree of freedom. The SM has precise predictions for all the
interactions of such a particle with all the other particles. Theoretical
predictions for various EW observables do depend on the mass of the Higgs
Boson, $M_H$. The SM predictions shown in Table~\ref{tab5} are calculated
using  a particular value for $M_H$.
Hence, these  precision measurements can in fact be used to derive and
`indirect experimental' upper bound on $M_H$. This can be then further
combined  with the experimental lower limit from the non-observation of the
Higgs boson in all the experiments (at LEP as well as at the Tevatron) up to
now. The range of $M_H$ allowed by the current experiments, at $95 \%$ c.l.,
in the SM is $115 < M_H c^2  < 150$ GeV~\cite{Moenig}. These limits are of the
same
order as $M_W/(M_Z) \simeq 84/(91) GeV/c^2$.  In particle physics parlance one says
that the experiments prefer a 'light' Higgs boson.
Without going into technicalities, let me also mention that in the SM the
mass of the Higgs boson is not predicted. But, pure theoretical considerations,
making no reference to the above mentioned precision measurements, predict lower
and upper limit on its mass.

Thus information available from earlier colliders in fact set the goals for
the LHC just like Gamow's theory predicted goal posts for energy required
for radioactivity. The physics flow between different machines  and their
implications for the LHC are summarised
\begin{figure}
\begin{center}
\includegraphics*[scale=0.6]{figs/acc-box-bw-small.ps}
\end{center}
\caption{The flow of physics information between different colliders
and their impact on design considerations of the colliders.}
\label{fig:accmh}
\end{figure}
in Fig.~\ref{fig:accmh}. Thus we see that results at the current series of
machines have always driven the physics at the next generation of machines,
giving an indication of the required energy/luminosity. The framework of the
SM was abstracted using results from the fixed target $\nu$ experiments and
from the low energy $e^+e^-$ colliders, DORIS/PEP/PETRA/TRISTAN. In that
framework one had a prediction for the masses of $W/Z$ bosons. The $UA$--$1$
and $UA$--$2$ experiments (UA standing for Underground Area) measured the
masses of these $W/Z$ bosons producing them directly, thus giving the first
`direct' confirmation of the SM predictions of these masses.
The combined measurements at the LEP-Tevatron, combined with high precision
theoretical calculations in the framework of the SM, then led to a prediction
of the top mass. The agreement of this predicted value of $M_t$ with the one
directly determined at the Tevatron (Table~\ref{tab5}), proved the correctness
of the SM to a high degree of accuracy. But these highly precise calculations
are possible in the
SM only if the particle spectrum of Tables 1 \& 2, is complemented by a Higgs
boson. These precision measurements and calculations, now predict the range
in which the  $M_H$ value must lie, in the SM. Further the theory itself
predicts that $M_H$ should lie in a certain range, SM or BSM, based on purely
theoretical arguments. To cover this entire mass range, then a high energy,
broad band hadronic machine is needed. The Tevatron does not have enough
energy for this purpose. This thus makes the case for the LHC. Of course
this will need to be followed by a TeV energy $e^+e^-$ collider, which is
already being planned as the LHC is running\footnote{This too is quite common
in HEP.  LHC planning was started, when LEP was in construction and the size
of the LEP tunnel was decided by keeping in mind that one would want to build
a LHC someday in the same tunnel.}.

\subsection{LHC design}
If the SM is correct a light Higgs (ie. with mass comparable to that
of the $W/Z$) {\bf must} be found experimentally.  There is strong evidence
that the SM is a very good approximation to reality. Right now  LHC is the
only collider which will be able to find a 'light' Higgs boson\footnote{The
Tevatron too can look for a 'light' Higgs but is not so effective in that
mass range and it is also not clear how much longer it will run.}.
\comment{
One should mention that both the experimental and theoretical limits
on the Higgs boson mass are different depending on whether there is
physics beyond the SM and what is the energy scale of this BSM physics.}
Even if the SM is not the entire story and hence the Higgs is not in the
low-mass range predicted by the SM or is not present at all, the success of
the EW theory in explaining the precision measurements indicate that
a `look-alike' of the Higgs boson must be present. The general theoretical
bounds on $M_H$ mentioned earlier, encompass those that one computes for the
`look-alike's as well. Hence, observation of the Higgs, measurement of its
mass or even the non observation in a given mass range, will shed light on the
puzzle of the formulation of a unified theory of electromagnetic and weak
interaction (EW theory) and the apparent mystery of the breaking of the
corresponding symmetry at low energies\cite{hinsa}.

It was clear while planning the LHC that one has to design the machine such
that it should be able to probe the issue in a completely model
independent fashion. A very general theoretical upper limit on the Higgs mass
is  about $900$ GeV. Even if the SM is not the complete reality, hence no
light Higgs boson is found, it would  still be possible to unravel the mystery
of the EW symmetry breaking by studying effective WW scattering at a total
energy of 1 TeV. The choice of energy and luminosity of the LHC was made by
by demanding that LHC should be able to cover this eventuality.\footnote{This
choice could be made even before the results of the precision measurements at
LEP were available to us, because of the general nature of the argument.}

It can be understood somewhat simply as follows.
\begin{figure}[hbt]
\begin{center}
\includegraphics*[scale=0.5]{figs/lhcdesgn.ps}
\end{center}
\caption{How LHC parameters were decided}
\label{fig:lhcdesign}
\end{figure}
The available knowledge of the quark/gluon content of the proton, indicated
that unlike the case of the earlier CERN and FNAL colliders, the physics
potential of the machine would be independent of whether one has a $pp$
machine or a $p \bar p$ machine. Hence a decision to make the, cheaper and the
easier to build , $pp$ machine was taken. Thus the LHC collides proton on
protons. As said earlier, the protons are made of quarks and gluons. Hence
the collisions at LHC, are effectively collisions among these quarks and
gluons. They carry only a fraction of the energy of the proton.
Fig.~\ref{fig:lhcdesign} shows a possible scattering process
$WW \rightarrow Z Z$. For the two W's to have a total energy of 1 TeV, each of
them must have energy of $0.5$ TeV and hence  each of the parent quark in the
figure must have energy of 1 TeV. From the measured distribution of the momenta
of a proton among its quarks, one knows that on the average, the quarks carry
about 1/6 th energy of the proton. This means that the protons must have an
energy of 6 TeV. Hence one planned on a $pp$ collision energy of 7 TeV on 7
TeV. The total number of $pp$ collisions were decided by using the theoretical
estimate for the rate of production of the events
$pp \rightarrow WW \rightarrow ZZ $  and demanding that  at least $10$ events
per year be produced. Note how our theoretical knowledge about the SM, has
set the bar for the new machine energy and intensity.

\section{LHC agenda}
\subsection{LHC agenda:SM}
Thus item number 1 on the LHC agenda is to find the Higgs boson and measure its
properties, such as mass and the interaction. The way the LHC has been designed,
at  its planned energy and luminosity, it will be able to search for the Higgs
boson over the entire mass range, allowed on very general principles,
irrespective of whether the SM is the whole story or otherwise. Due to the very
nature of the hadronic machine, LHC will be able to do the second job of
measuring its properties only to a  moderate accuracy of about $10 -20 \%$. A
more accurate measurement has to wait for the next generation $e^+e^-$
collider which will have less energy than the LHC, but the measurements will be
much cleaner and more importantly the LHC would have indicated to us the Higgs
mass and hence the optimal energy to run the machine.

I have focused here on what I believe to be the main reason for planning and
executing this mammoth project. Interestingly, however, it transpires that the
LHC will also offer almost a direct  probe into what went on in the early
Universe, in addition to the indirect probes that I have talked about. This
will happen in the `heavy ion avatar'  of the LHC, where instead of protons,
relativistic heavy ions will be colliding against each other. These collisions
will recreate energy densities that exist in the early Universe. In the
presently accepted description of the early Universe in the Standard Model of
Cosmology, the early universe is a hot, radiation dominated plasma, which is
an 'almost' an ideal gas.
\begin{figure}
\begin{center}
\includegraphics*[scale=0.5]{figs/qgp-small.ps}
\end{center}
\caption{Depiction of different stages in the evolution of the Universe}
\label{fig:qgp}
\end{figure}
This picture, shown in Fig.~\ref{fig:qgp}  has been verified up to a temperature
of  $\sim$ 1 MeV, i.e. the Nucleosynthesis period as mentioned earlier.
The period before that
is opaque to current astrophysical measurements. In Heavy Ion Collision option
one can recreate the transition from the state of a quark-gluon plasma to the
currently known hadrons. Thus the LHC can create a `mini-bang' as opposed to
the big-bang which started off our Universe. Study of this transition will
also offer a look into the strong interaction dynamics in a region that so
far has not been accessible to our experiments and which also poses challenges
to the theoretical computation techniques.

The next question to ask is, will it be enough for the particle
physicists if a  Higgs boson were to be discovered at the LHC with precisely
these properties, in precisely this mass range? Will that conclusively
complete our understanding of the fundamental interactions among fundamental
constituents of all matter? In other words, what is the need for going beyond
the standard model, the BSM physics, that I have been mentioning.

\subsection{BSM physics}
There are a variety of reasons which have prompted particle physicists to look
for ideas beyond the SM. Majority of these reasons are aesthetically. But a lot
of progress in particle physics (and in fact theoretical physics) has come from
looking for elegant explanation of observed physical phenomena and properties.
For example, $1/r$ dependence of the Coulomb Potential is due to the
'zero' rest mass of the photon and zero rest mass of the photon is due to
the fact that Maxwell's equations have gauge invariance. Thus in this case,
the principle of gauge invariance 'explains' the experimentally observed nature
of Coulomb Potential and zero rest mass of the photon. Similarly, as described
in the earlier subsection, the precision testing of the SM, implies that
a Higgs OR a look alike must exist and data tell us it must be light!
Just like gauge invariance gave an explanation of the power of $r$ in Coulomb's
Law, we would like to understand why the Higgs is light!! Particularly so
because, a quantum field theory of spin 0 particles would predict that
the Higgs should be as heavy as can be!!!\footnote
{If one likes one can interpret the direct/indirect experimental indications for
a `small' higgs boson mass  as a 'disagreement' with the SM.}
This is one of the `theoretical' reason for expecting BSM physics.

Among the experimental hints for BSM, the most significant is the existence
of `invisible' Dark Matter' (DM) in the universe. Since, this DM can not
consist of the particles of the SM,  it is a clear indication for
BSM physics. It is a matter of enormous interest, that almost all the BSM
physics scenarios, `naturally' have a particle that could be the DM in the
Universe.

Second experimental hint of BSM physics is the nonzero, tiny mass
of the neutrinos. It is now firmly established that neutrinos have tiny,
nonzero masses {\it and} the masses of the fermions have a huge hierarchy.
For example the mass of neutrinos is smaller than $1 eV/c^2$ and mass of
the top quark is $\sim 175 \times 10^9 eV/c^2$.
In the SM all these masses are just arbitrary parameters.  A natural question
that has been asked by particle theorists, is whether we can have a fundamental
understanding of why they have the values they have? Such questions might
sound esoteric, but a lot of progress in science actually has come from asking
such questions. Neutrino masses are especially tiny and being neutral,
it is possible to have elegant mechanism for generating these `small'
masses almost `naturally' in some BSM formulations.

Further, unification
of all interactions into one master interaction is a dream which even
Einstein had had. At first level, unification of weak and electromagnetic
interaction in a single Electroweak interaction, has been observed. All the
three interactions do not unify at a given scale if there are no more
fundamental particles in addition to those in the SM, whereas
such a unification is possible in BSM scenarios. This is one more
`indication' of BSM physics. It may be added at this point, that almost all
the models which attempt to explain the observed pattern of fermion masses
quite often use the framework where the interactions do unify at a high energy
scale.  Such theories also have mechanisms which can explain the observed
matter- antimatter asymmetry in the universe or a candidate for dark matter,
almost automatically.

It is worth observing that that both the experimental
and theoretical limits on the Higgs boson mass can depend on the (non)existence
of the BSM physics and its energy scale, if it should exist. Hence observation
of the Higgs and a measurement of its mass can tell us a lot about the energy
scale and nature of BSM physics that might exist. This is like trying to
decipher the nature of the animal being tracked from its footprints.
A brief discussion of some of the theoretical options for the BSM physics
that have been proposed is given in Box-II.

\subsection{LHC agenda: BSM}
It should be clear from all these discussions that the
the job of the LHC is not finished even when it finds a light Higgs
boson. If it is indeed in the mass range that the earlier collider
experiments have indicated, the theory  must then explain why it is light!
Different explanations of why
the Higgs is light imply new symmetries, new particles exactly at the TeV scale
which should be observed at the LHC.  So if a light Higgs boson is found
the next item one on LHC phenomenology agenda is to infer which one of the
many explanations (if any) is right.

A natural question is what if we
don't find it?  It would mean that there is an alternate to EW symmetry
breaking which passes the challenge posed by the precision tests as
comprehensively as the SM does.Then the LHC agenda item is to check which
one of these alternates, if any, is correct !  So one of the big area of
phenomenological research has been how to delineate different BSM ideas
from each other~\cite{belyaev} at the LHC.

From the discussions of the different BSM physics scenarios it is clear that
the hunt for these BSM scenarios may in fact  help us explore further
at the heart of matter and probe the structure of space time. Most of the time
due to the very nature of these BSM ideas, they have implications for the
early Universe and hence this is an opportunity to test some of
the ideas of the Standard Model of Cosmology at the LHC.

I reproduce below a list of objectives that have been set out in a road
map of particle physics for the next decades by the world community.
\begin{itemize}
\item Are there undiscovered principles of nature:
      New symmetries, new physical laws?
\item Are there extra dimensions of space?
\item  Do all the forces become one?
\item Why are there so many kinds of particles?
\item What is dark matter?
      How can we make it in the laboratory?
\item What are neutrinos telling us?
\item How did the universe come to be?
\item  What happened to the antimatter?
\item How can we solve the mystery of dark energy?
\end{itemize}

Apart from the last point in this list, we expect the LHC to shed light
on almost all the points. That is the reason LHC is the watershed experiment
in Particle Physics. All of us are looking to it to point the way ahead.!

\section{LHC machine and physics: time line}
\subsection{LHC machine: accident and repairs}
Even by the standards of HEP laboratories designing and building the
Large Hadron Collider was a challenging exercise. As said above, LHC was
conceived in 1980s and  the planning
began already in 1989. The tunnel which houses the LHC now, was built
between 1983-1988  and was home to the LEP experiment till 2000. CERN Council
approved construction  in 1994. Limiting oneself to the use of the LEP
tunnel meant that there was an upper limit of 7 TeV to the energy to which
the protons could be accelerated\footnote{To reach the same physics goal of
being able to hunt for the Higgs up to the general upper limit of about 900 GeV,
the then under planning and later canceled, Superconducting Super Collider
(SSC) project in USA, was supposed to accelerate the beams to an energy of
20 TeV in a much bigger tunnel.}. Hence the LHC had to plan on larger
luminosity. This meant smaller
bunches, higher magnetic fields and  packing more particles per bunch. The
LHC builders then decided to use new methods for acceleration. They
also  decided to use a very
innovative idea where the beams would circulate in two separate rings
just above one another. For $e^+ e^-$ or $p \bar p$, the same magnetic
field automatically suffices to steer the two bunches in opposite directions.
That is not the case when both colliding particles have the same charge as they
do for the LHC. All this was not just technologically challenging, but also
expensive. The decision was then taken by the CERN Council to build it in two
stages. In the meanwhile plans for the SSC were abandoned. From  1995 onwards,
countries which were not members of CERN, viz.,  Japan, USA, Canada,
India and Russia, promised support to the LHC machine and decision was
taken to do it in one go. While the Indian HEP community had participated
in building detectors  and doing experiments at the earlier fixed target and
collider facilities,  this was the first instance where India participated
in the building of the machine itself.

Given the ring size and the energy to which particles needed to be accelerated,
meant that one needed to have higher magnetic fields of about $8$ Tesla. This
in turn  meant that the magnets had to be cooled down to $1.9^{\circ}$ K.
Contrast this with the other superconducting collider Tevatron where this
temperature is about $5.2^{\circ} K$ and the magnetic fields required about a
factor two smaller. The magnetic fields required at the LHC are also higher
than the one used at the old SPS, by about a factor 5. Not just that, 10-12
Tesla is about the upper limit at which these Niobium-Titanium accelerator
magnets can function, still remaining superconducting. All this should give a
flavour of the engineering and technological improvements that were required
for the LHC. The most crucial piece of the machinery for the LHC are the 1232
dipole magnets, each weighing 34000 Tonnes and costing about 0.5M CHF each.

Before the start up of September 2008, the energy goal was already lowered from
the initial $7$ TeV to $5$ TeV, with plans to raise the energy afterwords. Its
start up in September 2008, came to an abrupt end during a test of {\it
the} one sector which had not been tested before for the full current
corresponding to an energy of $5$ TeV. Most likely, an electrical arc
developed and it punctured the Helium enclosure.
Large amounts of Helium gas were released into the insulating vacuum of the
cryostat and a large pressure wave traveled along the accelerator both ways.
The pressure was too large to handle for the pressure release systems which
had been put in place. One of the quadrpole-dipole connection, before and
after the  incident is shown in
\begin{figure}
\begin{center}
\includegraphics*[scale=0.47]{figs/interconnect-small.ps}
\includegraphics*[scale=0.42]{figs/cryodipole-small.ps}
\end{center}
\caption{The quadrupole-dipole connection: undamaged  and damaged in the
left and right panel respectively.
}
\label{fig:cryodipole}
\end{figure}
Fig.~\ref{fig:cryodipole}. The severity of the accident becomes obvious when
one recalls how heavy these magnets are. Thirty nine of the 1232 dipole magnets
and 16 of the quadrupole magnets had to be replaced, vacuum tubes had to be
cleaned, new pressure release systems as well more diagnostic methods to avoid
a similar accident again, had to be installed. All these repairs were
completed by fall 2009. A large
amount of time is required to cool the machine to the low temperatures,
which has to be done gradually. Finally  by the end of the November 2009,
the machine was ready to go again and as said in the introduction the
collisions have taken place. However, it is noticed that the Superconducting
magnets need to be `trained' to carry higher currents and hence the
ramping of the energy will now be gradual. Initially now the machine will run
only with beams of $3.5$ TeV each (exactly half the design energy and less than
the $5$ TeV which was planned for the 2009 run). It is now proposed that the
machine will run at this energy till end of 2011 and then again there
will be  a major shutdown to ramp up the energy up to 6.5 to 7 TeV per beam,
(the 7 TeV looking a bit difficult to reach as per present studies), as well as
an increase towards the ultimate design luminosity, of
$10^{34} cm^{-2} sec^{-1}$. (This was the number that I had used in
explaining how the LHC design energy was decided.) Now it is foreseen that
the design energy and luminosity, will be only reached,
after a period of about two years, as per current plan.

It should be mentioned that for this low energy run, a reduced luminosity of
$10^{32} cm^{-2} sec^{-1}$ is foreseen. However, as I write these lines,
only a luminosity of $10^{30} cm^{-2} sec^{-1}$ has been achieved.
This is partially because these big machines are like a delicate musical
instrument which needs to be finely tuned. For example, when larger
number of bunches are injected, to increase the luminosity, the
bunch-bunch interactions can destabilise the beam. These interactions are
understood, in principle, and included in the designs; still fine adjustments
to the beam parameters are required to get rid of these effects while the
machine is running. Right now  accelerator experts are working on it,
alternating their work with giving the beam for actual physics run to the
experimental physicists. The bunches with the LHC design intensity (i.e.
$ 1.15\times 10^{11}$ p per bunch), have already been successfully injected. To
increase the luminosity one would need to increase the number of bunches. After
beginning with one bunch, they had gone up to  13 bunches with $\sim 10^{10}$
ppb and 7 bunches for the $\sim 10^{11}$ ppb. The goal is to reach 2808 bunches
The possible time line of the expected physics results will in fact
depend very much on the success of this tuning procedure. In the following
I shall assume that in a few months at least a luminosity of few times
$10^{31} cm^{-2} sec^{-1}$ will be achieved.

\subsection{Possible time line of Physics results}
As mentioned already, an evaluation of how well the mammoth detectors can
achieve their goals, requires precise theoretical predictions. A large number
of very detailed analyses, with the combined participation of the theorists
and experimentalists alike were done to analyse the physics prospects of the
LHC~\cite{TDRS}. Most of the very detailed analyses used the nominal
LHC energy of $14$ TeV and the nominal luminosity of $10^{33}$ -- $10^{34}
cm^{-2} sec^{-1}$ in the first year. The value at the lower end means
that there will be $10$ events per year ($\sim 10^7$ sec = 150
running days in a year), per $fb$ cross-section. This is
termed as luminosity of $10$ fb$^{-1}$ per year.
\begin{figure}[hbt]
\begin{center}
\includegraphics*[height=11cm,width=9cm]{figs/lhcallx.eps}
\end{center}
\caption{The cross-sections for various processes expected at the LHC.}
\label{fig:lhccsec}
\end{figure}
The number on the right hand side indicates the number of events for
a particular process for the lower value of the nominal luminosity of
$10 fb^{-1}$ or equivalently $10^{33}cm^{-2}sec^{-1}$.

One can see, from the figure that even at the high energy and luminosity,
finding a Higgs with the lowest mass that is allowed for it by experimental
constraints is not an easy job. For example, for a Higgs with $M_H c^2 = 150$
GeV, one expects only a handful of events where a Higgs boson is produced.
\footnote
{Further, when one multiplies it with the probability that it will give rise
to an event that can be distinguished from the background the number falls
to may be an event or less a day.}
One can see that the cross-sections for different processes
fall with varying factors as the collision energy is lowered. However, just a
simple scaling by this factor is not enough to judge the change in sensitivity
due to the present reduction in the energy and luminosity, as the background
processes in general have a slower fall off with the reduction in energy
than the signal process of interest.

So in the short run, ie. in the next two years, with the machine delivering at
the most, a luminosity of
$10^{32}cm^{-2} sec^{-1}$, one is not likely to see a signal for the SM
Higgs boson, if it has mass in the range indicated by the current experimental
constraints\footnote{It is interesting that already with the luminosity of
$\sim 50$
nb$^{-1}$ that has been delivered the LHC could already have produced one event
of the type $p + p \rightarrow h + X \rightarrow b + \bar b +X$,  if its
mass is around $120$ GeV. Unfortunately, the background is too huge in this
channel and the ONLY promising channel for such a light Higgs, is when the $h$
decays into  $\gamma \gamma$  final state and such events will happen at a rate
1000 times smaller.} There is a possibility of detecting the Higgs, even for
this 'low' luminosity, if its mass is
around  $160$--$165$ GeV, but the Tevatron data has ruled out existence of a
SM Higgs in this mass range at $95\%$ c.l. However, due to limited statistics
and the theoretical uncertainty in the prediction of cross-section, this limit
has to be taken with some reservation~\cite{Baglio:2010um}.

Luckily, the production cross-section for the different varieties of new
particles that are expected in the different BSM scenarios, go down much more
slowly with energy. For example, even with this lower luminosity and energy,
the LHC has a chance to `discover' Supersymmetry if the masses of the strongly
interacting super-particles are less than $800$ GeV, about twice the current
limits from the Tevatron Collider. So clearly the possibilities for the BSM
physics are quite tantalising even at the lower energy/lower luminosity LHC.
Thus the search for the Dark Matter in the Universe at the LHC can already
happen in these two years. One good news is that the detectors are working
perfectly and are able to  remeasure the SM processes well, to calibrate
the SM backgrounds to the new physics searches using the experimental results
themselves.

The studies for the Quark Gluon Plasma formation (and hence recreating
the situations in the early Universe) should not be affected in a major way
due to the energy reduction. Thus the heavy ion program and the $LHC_{b}$
program (to study the issue of CP violation and flavour physics at the LHC),
also should not be affected in a big way due to the reduced LHC conditions.

Whether the Higgs field is an elementary particle as in the SM or a`look-like'
which may not be elementary; whether there is only one or there are more of
them : elementary or composite; one thing is for sure, the problem of
reconciling a left handed world with massive matter particles, requires
existence of a new phenomenon and the LHC has been designed to solve this
enigma. However, we need to be patient, given the complexity of the problem,
the rarity of the phenomena that we need to analyse to get the answers, along
with  the reduced energy and luminosity. Several years of data-taking and
analysis will be needed to sort out the puzzle.

It is heartening that Indian experimental groups have been contributing to
building the detectors and doing experiments with the $pp$ as well as the
heavy ion collisions. Further, the Indian theoretical
physics community is also involved in a big way in LHC physics, be it the
SM, BSM physics in $pp$ collisions with the CMS/ATLAS detector, or the
B-physics in $LHC_{b}$ or the physics of the QGP in the heavy ion mode.

After a shutdown that is planned at the end of 2011, the machine physicists
will work on getting to the higher energy. Once that energy is reached, LHC
should be able to full fill its promise of hunting for the Higgs over the entire
mass range allowed for it theoretically, which is indeed the  `Raison de tr\'e'
of this machine. So in short this complicated exercise is sure to keep the
particle physics community busy for a decade or two and yield answers to some
of the basic questions about the very fabric of space and time and the
Universe we all live in, as the particle physicists travel in this 'terra
incognita'. In all probability it will throw up some unexpected results,
which in fact will point the way ahead in this journey towards truth. Exciting
times are ahead for sure !

redpajama_set_name: RedPajamaArXiv


Leveraging on the experience and knowledge derived from manufacturing, we have set-up a dedicated R&D center located in Rajpura, which is approved by the Department of Scientific and Industrial Research, Ministry of Science and Technology, GoI ("DSIR"). This center is equipped with a 3D modeling and product lifecycle management software and has access to equipment such as 3-D CAD, 3-D printers, psychometric labs which are accredited to ISO/IEC 17025:2005 by NABL, anechoic sound proof room, reliability test lab, rain test chamber, humidity chamber, TIR tester and PCB on-off test Infra. Design capabilities of the Group encompass all the verticals of RAC – Finished goods in window air conditioners , Split fixed speed & split inverter , Sheet metal components , Copper tubings , Heat exchangers , moulded plastic components.
R&D capability is further backed by in-house tool room for sheet metal parts . All the platforms are designed & tooled up locally – providing overall flexibility & efficiency in system in terms of response , improvisation & cost .


After breakfast, explore Luang Prabang. Start with a visit to the National Museum, which used to be the former Royal Palace. Inside the complex of the museum you will see the "Prabang", or the sacred golden statue, giving its name to the town. Continue to Vat Mai, the former royal temple, which is Luang Prabang's largest and most decorated temple. Not far stands Vat Sene, which is considered to be one of the most beautiful temples in town, with its red walls and golden bas‐reliefs. The nearby Heritage House is a perfect example of Luang Prabang's traditional building style and is made of wood and stands on poles. Admire the complicated architecture style and learn why many houses in Laos, but also in neighboring countries were often build on poles. Visit afterwards the TAEC, the Traditional Arts and Ethnology Centre. The center depicts Laos' rich ethnic diversity with themed rotating exhibits. It is hosted in the former French colonial mansion of a judge. Continue to Vat Xieng Thong, one of the most emblematic temples in Laos. It is located at the top of the peninsula, where the Mekong and Nam Khan Rivers meet. If time allows, visit also Vat Visoun and Vat Aham. Both are historically important pagoda's based on what they represent.
At the end of the tour, climb Mount Phousi in time for an incredible sunset view of the town and its surroundings. After sunset, climb down the stairs and find yourself in the middle of the local hill‐tribe night market, which every night lightens up the central part of town.


When George accompanies The Man in the Yellow Hat to Dr. Baker's office for his annual check-up, he discovers that a stethoscope is a pretty handy thing to have around! Curious George | English Full Episode | Funny Cartoon For Kids ► Subscribe to the Curious George Official channel for many full episodes every week: http://bit.ly/2fNhwJS ► Watch Curious George Official Video here! ► Watch All Videos Curious George Official Full Episodes: http://bit.ly/2yIkYZR ► Watch More Curious George Official Compilations: https://goo.gl/6VES3A Curious George Season 4: George becomes a personal trainer for Professor Wiseman, goes on a Junior Sprout field trip, helps restore a classic movie theater, and is the special guest monkey at Allie's kindergarten! Curious George is a sweet African monkey who can't help but run into trouble. George's friend, "The Man in the Yellow Hat," tries very hard to care for George and is always saving the day. The show's themes are about learning, forgiveness and playful curiosity.
Doctor Who Animated [Part 3 of 4]: "TRY-ON FOR SIZE"
The Doctor and Amy encounter another Youtube menace - The Try-On Haul.
#DoctorWho #PeterCapaldi #JodieWhittaker #bilgriffin fan fiction The Adventures of two non-Gallifreyan Time Lords, one of whom is often mistaken for The Doctor. Doctor Who meets Monty Python. References to Terry Jones in the Life of Brian and The French Taunting in Monty Python and The Holy Grail in the context of The Magician's Apprentice.
Doctor McWheelie & Multi level parking. Cartoon for children.
Olivia the Pig | OLIVIA THE DOCTOR | Olivia Full Episodes | Cartoons for kids | NEW EPISODES ► Click to Subscribe to Olivia the Pig Official: http://bit.ly/2syMvL3 Warm Welcome to the Official Channel of Olivia The Pig Cartoon! Enjoy Olivia the Pig full episodes and compilations. Olivia is always up for fun, if it's at school, at home, or at a friends house! Join her on the next adventure! ► Watch more Olivia the Pig Full Episodes: http://bit.ly/2rI5G5n ► Watch Olivia the Pig 'makes'... http://bit.ly/2szMWFf ► Watch Olivia The Pig - Brand New Collection of Favourite Episodes http://bit.ly/2sczFF4 ► Meet the Characters! ► Olivia - Today's girl. A 6 ¾ year old dynamo who believes she can do anything and sees every day as an opportunity to try new things. ► Mother - Supportive and loving, but no-nonsense — the glue that holds everyone together. ► Father - Warm, loving, affable dad who enjoys spouting factual information and drawing graphs to illustrate his point. ► Ian - 4 years old, and Olivia's older younger brother, Ian is particularly interested in space, dinosaurs, robots, and managing spaghetti eating. ► William - A small baby that does what most babies do. He sleeps, eats, cries and can be quite adorable. ► Grandma - stylish and in her late-fifties; appreciates everything from Tai Chi to surfing and calypso dancing.
Doctor Da Kutta Happy Ne Maareya | Happy Sheru | Funny Cartoon Animation | MH ONE Music Happy Singh, Lucy, Billo, Sheru, Lilly, Angrej Singh, Kukkad, Happy's Mother And Many More Are World Renowned Fictional Animated Characters Conceived and Created by MHONE Music Channel, a Leading Satellite Channel Patronized by the Punjabi Music and Film Industry. This is the Most Popular Punjabi Animation Video.This is the Biggest Hit Punjabi Animation Show. This Super hit Punjabi Animation Video is available for Free Online Watch on YouTube. Subscribe Us On:- https://www.youtube.com/channel/UCeWsdNoxtR8_nsH7wBQAB5Q?sub_confirmation=1 Our Website :- http://www.mhone.in Follow Us On:- https://www.twitter.com/mhonemusic Like Us On:- https://www.facebook.com/mhonemusic Like Us On:- https://www.facebook.com/happysinghmhone Thanks for watching !!!!! Like and Share your Favorite Cartoon Show Happy Sheru !!!
Cartoon #106 - The Doctor wants to capture the treasures of a mysterious island!
Other cartoons ------------------- Tornado in the city? Who did this? Monster Machines. New cartoon for kids - https://youtu.be/d28e7DqmhQ0 Doc plays his game and wants to capture the city. Handy Andy and his flying car come to the rescue. - https://youtu.be/QDygGXigiNU ____________ Major Harry (seriously): Handy-Andy, you were going to go to the port and shoot seascapes? Handy-Andy (jokingly): Yes! Major Harry (seriously): Observe the situation then, and the Officer will arrive a little later. Handy-Andy (fun): No problem! Handy-Andy comes out of the station and sits in Megamax. Port. Doctor and Irma. Dr. Evil (ominously): Great weather, I didn't even have to do anything ... Irma (perplexed): I still did not understand how you are going to pick it up. Dr. Evil (arrogant): It's not for your brain ... well, I will explain. In the 9500 BC (further per frame) there was an island-state of Atlantis. The descendants of God of the seas of Poseidon inhabited it. There were many statues on the island and golden and silver temples. And the device, the exact purpose of which is unknown. Irma (thoughtfully): Eeeeeee .... And you need this device? Dr. Evil (gambling): Exactly! Irma (excitedly): But if noone knows its purpose, then maybe you shouldn't turn it on, what if something terrible happens? Dr. Evil (irritated): Something terrible will happen if you don't stop bothering me! And now let's start! Irma pushes into the water device, similar to the drill. Doctor holds remote control. Irma (hard): This device will make a strong push and the island rises from the depths of the sea? Dr. Evil (seriously): Yes, and we will sail and quickly examine everything, we will have a little time, so get ready. The doctor presses the buttons on the control panel. Pierce shudders. Dr. Evil (excitedly): Started, let's go! They jump into the boat and quickly move away from the shore. There is a map left on the pier, twisted into a tube. Megamax flies to the shore. Handy-Andy (fun): Great place, so, and what's that? Handy-Andy with a camera around his neck picks up a map and unfolds it. Handy-Andy (thoughtfully): It can't be possible, but it's not here ... although no one knows the exact location ... He looks into the distance. An island is beginning to appear on the horizon. Handy-Andy (excitedly): According to legend, there was a device on the island capable of great things, only it is unknown whether it was good or bad. And there was some reason thet Atlantis sank, you need to stop the Doctor! Handy-Andy jumps into Megamax and flies towards the island. Handy-Andy (on the radio) (alarmed): Major Harry, this is ... send a helicopter! At the station. Major Harry (perplexed): Has anyone gone to sea in such bad weather? .. Handy-Andy hovers over the island without landing. Handy-Andy (indignation): Well, how do you immerse it back? The doctor and Irma are already nearby. Irma (lively): Look, Doctor, Handy-Andy is here too! Dr. Evil (sarcastically): What a joy ... Surely he will try to spoil my plan! Speed up! The boat is accelerating. Handy-Andy (excitedly): And here is the Doctor! It is necessary to detain them, the island will not be able to remain on the surface for a long time, in a couple of minutes it will be pulled to the bottom by an ancient curse, because of which Atlantis sank along with all the inhabitants. Handy-Andy flies to meet the boat. From Megamax falls hook on the cable and catches the boat. Handy-Andy (glee): Gotcha! Handy-Andy begins to pull the boat behind him and drives it across the sea. Dr. Evil (indignation): What is he doing? Irma (ironically): It seems, giving us a ride ... The sea shudders. The island begins to sink under the water. Dr. Evil (indignation): Oh no! Irma (cheering): Well ... we can try tomorrow! Dr. Evil (indignation): It can be raised to the surface once every 1000 years, and even then if you do everything right ... Handy-Andy (glee): It worked! At this moment a submarine appears from under the water. Irma (ironically): Perhaps we should go! Dr. Evil (maliciously): Now do you understand how important it is to have a fallback alternative? They jump into the boat and hide under the water. Handy-Andy (disappointed): Gone ... A police helicopter arrives. Officer (alarmed): Handy-Andy, what happened? Handy-Andy (discouraged): Atlantis just rose from the sea! Officer (ironically): And yesterday I saw the mermaids, what a joke, today is not April 1st! (the officer starts laughing) Handy-Andy sits with an Emmy on the pier. Emmy looks at the photo that he made. There is a sea, waves, gulls; and here comes a photo of a statue from the island. Emmy (surprised): Handy-Andy, you don't want to tell me anything?
DOC2DWHO - The Astonishing Custard Cookie Chase | A Doctor Who cartoon for Kids.
The Doctor races Tim Shaw across a mysterious Desert Planet to win the big prize! A Doctor Who cartoon for Kids. Doc2DWho is a fan made Doctor who cartoon, all characters belong to the BBC. Visit http:www.froggtreecomics.com for more DOC2DWHO free comics!
Cartoon Animation for kids with Kids Play Football ⚽3-series successively !!!!
Hi Kids !!!! This is a collection of cartoons about Kids who always comes to the rescue . We have tried to collect in this video for you all the fun and positive that you liked . Be kind and responsive to people . Eat more fruits and vegetables in them a lot of vitamins . Enjoy viewing our little Friends !!! 💋 🚓 Hurry and sign here : https://goo.gl/eSAvW5 👲👮 About the Little Heroes to the Rescue 🚒🚓 : * Hi guys:) We welcome you to our little heroes to the rescue ! The concept of our channel is to teach you how to react in any situation in which your friends or just passers-by ! * We want to show you how to act when meeting a thief, or if there was a fire, and who can help if your car is broken or need to build a house . Don't forget that if you need help, you can call 911 or ask for help from adults. * Our young heroes are 2 brothers who dream to become real heroes ! Our story Cartoons for kids, maybe a new format, created by us and are all made using editing programs and toys for kids ( because they are all virtual and fictional characters for us ) * We want to show that any profession you choose when you grow necessary and important ! Firefighters extinguish a fire , the police catch criminals that may offend anyone, the builders build houses, and the mechanics will repair any equipment .
Hi guys eat more fruits and vegetables , they have a lot of vitamins . And be healthy ))) 🚓 Hurry and sign here : https://goo.gl/eSAvW5 Hi guys eat more fruits and vegetables , they have a lot of vitamins . And be healthy ))) Enjoy viewing our little Friends !!! 💋 👲👮 About the Little Heroes to the Rescue 🚒🚓 : * Hi guys:) We welcome you to our little heroes to the rescue ! The concept of our channel is to teach you how to react in any situation in which your friends or just passers-by ! * We want to show you how to act when meeting a thief, or if there was a fire, and who can help if your car is broken or need to build a house . Don't forget that if you need help, you can call 911 or ask for help from adults. * Our young heroes are 2 brothers who dream to become real heroes ! Our story Cartoons for kids, maybe a new format, created by us and are all made using editing programs and toys for kids ( because they are all virtual and fictional characters for us ) * We want to show that any profession you choose when you grow necessary and important ! Firefighters extinguish a fire , the police catch criminals that may offend anyone, the builders build houses, and the mechanics will repair any equipment .


text:
If you would like to pause your VM when not using it:

1. Go to the Google Cloud Platform Console and select your project: https://console.cloud.google.com/project/_/compute/instances
2. Click on the checkbox next to your VM.
3. Click on *Stop* to pause your VM.
4. When you are ready to use it again, *Start* your VM.  For more detail, see: https://cloud.google.com/compute/docs/instances/stopping-or-deleting-an-instance

If you want to delete your deployment:

1. First copy any data off of the data disk that you wish to keep.  **The data disk will be deleted when the deployment is deleted.**
2. Click on `Deployments`_ to navigate to your deployment and delete it.

redpajama_set_name: RedPajamaGithub


Happy Monday! Well I took some time off last week, and with all of the activities and traveling…I'm still exhausted! I don't know why, but do you ever feel like you need a day to recover after a vacation? I always do. It never fails, I'm always tired. However, this trip isn't a fair comparison to other trips because we traveled home to Kansas City. It's where we both grew up, so there a ton we have to fit in in such a short amount of time. On top of all of the holiday activities. Needless to say, I am back to work today and all I want is another day or two to lounge around. So I am sharing some of my favorite athleisure items for the week.
I am obsesses with these Spanx leggings. I have them in two color and wear them so much. They do have a heftier price tag, but you won't regret these babies. Especially now after the holidays. If you're like me, I can use all the help I can get sucking in all those extra holiday treats I took in! Also, I would say I wear these at least 2 times a week and have since I got them last year. I would my price per wear has to be pennies by now. Bonus: they hold up amazingly well with washing and drying!
I am also loving all the cozy sweatshirts, and I love that it's stylish and acceptable to wear them. Somewhere after college it became not cool to wear hoodies and sweatshirts outside the house unless you were totally slumming. We Mama's it's definately not the case anymore. With so many cute options out right now you can pair it with leggings and sneakers, skinny jeans and Uggs or even booties. This exact one is from Modish Boutique, but linking up some other favorites below.
Lastly, it's all about sneakers! The key to pulling off sneakers and still get that casual chic look is to pick one that's not bulky. So many athletic shoes have thicker soles to make working out more comfortable. Well that is not the sneaker for a pulled together athleisure look. There are so many options that are smaller soles, not as wide around your foot and are super lightweight. I have had these Nike sneakers for almost three years. Yes, they really can hold up for a while, and snagging a black pair is such a closet staple!
Here are a couple of looks I put together last year wearing the faux leather Spanx. You can wear them super casual like this or this. If you want to dress them up this and this are also great ideas.
So, are you an altheisure kind of person? Are you as pumped as I am to know this is really acceptable and on trend? I's love to hear your thoughts on the trend so leave a comment below!
I definitely hear you on needing a vacation from your vacation! The older I get the more days I seem to need, much like having too much fun on an evening out, 😂😂😂. Also, comfy clothes and chilly weather just seem to go hand in hand. Perfect outfit.
Now that's a fun sweatshirt, I love it! And yes to Nikes! They're so comfortable to wear.


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Divinity: Original Sin 2 Review
Dom Peppiatt | September 19, 2017 2:17 pm BST
Very well-written
Can be hard to penetrate
Occasional graphical bugs
Divinity: Original Sin 2 - Definitive Edition Videogames 722674122344
Divinity Original Sin 2 [LP] - VINYL
Available on PC
One of the most impressive things about Divinity: Original Sin 2 is how amazingly flexible the game is. There are so many various elements that can be customised, altered, tailored to your personal tastes. Even from the very start – when you set up your character and decide your origins – you realise that this is a true RPG: it's a game that wants you to decide the role you're going to play, and stick to it. And the tools it gives you to do this are impeccable.
But where Divinity: Original Sin 2 differs from so many other RPGs out there is that it's hilariously unpredictable, for better and worse. You can be the most prepared player in the world, and Original Sin 2 will still find a way to test and surprise you. There are so many skill trees to master, so many weapons to use, so many combat disciplines to put to use in a fight, but sometimes you'll find yourself lacking the one skill you need to take down an enemy.
Related: Best games of the year
But that's why Original Sin 2 excels as far as game design goes: it makes absolutely everything you do feel like it has consequence. You can trade an item that seems like junk to a merchant and realise perhaps 10 hours later that little locket was the key to a quest you haven't even discovered yet. You can learn a healing spell and use it on an NPC in the town and be richly rewarded. You can accidentally put the spooks on someone by unsheathing your sword and get a whole town trying to brawl with you. It's a wonderfully interactive game, and the world bristles with life in every new area you discover.
The fact that the world is so large and adaptive becomes even more impressive when you consider how differently everything can react to you based on what origin you give your player character. Considering you might accidentally kill an NPC that wants to give you a quest, you could be an Elven character with a trait that lets you access the memories of the dead… by eating them. Or you could have a perk – Pet Pal – that lets you talk to animals, and an animal that knew the quest-giver might be able to pass on the information you need.
Even from the very first decision you make in the game, you'll find yourself getting repercussions later on – and that's impressive. Something so innocuous (like choosing your favourite instrument) can fundamentally affect how the game plays out to you, and the experience you have with it. Developer Larian seems to have considered every outcome, and has anticipated every strange decision that might go through your head. You can push this game as far as you want – you can really, really try and mess it up, but Divinity: Original Sin 2 has an answer for everything.
Related: Middle Earth: Shadow of War preview
Even when it comes to boss encounters, Larian seems to have composed the game with a wicked sense of humour. Unlike a lot of triple-A RPGs, you don't always have to resort to murder in order to progress. Yes, combat is a big part of the game (and admittedly it can occasionally be dull), but as far as actual story beats and plot points go, you'll find yourself rarely needing to kill something to be rewarded with plot or loot.
Bluffing your way through conversations or dealing with antagonistic characters that hate your guts because of your chosen origin is probably where the game feels at its most pure: there are so many dialogue options and so many unique responses NPCs will have, you'll be shocked by how different a second play through with a second character will feel: it's like a different game. A one-time purchase of Divinity: Original Sin 2 will provide value for months if you're the sort of player that wants to experience everything a game will give them.
Case in point: one play through can see you enter a cave and wipe out all the henchmen in it because they're simply in your way. In another play through, you might find out that your character has something in common with one of the guards, and that cave could become like a proxy home to you. The variation from one game to another is, frankly, astonishing.
Related: South Park: The Fractured But Whole preview
This variation is deepened whenever a new character comes to join your crew – as soon as they're in your party, you get to choose their class. It seems like a small thing, but Bethesda and BioWare should take note: it's a game-changer as far as RPG setups go. It allows you full control over your experience, but you need to read ahead: one wrong move can make the game incredibly difficult for you.
And that, really, is the only place Divinity: Original Sin 2 falls down. Thanks to the game's incredible density, you can often find it hard to progress. The game can throw so much at you that, sometimes, it can be overwhelming and you have no idea what to do next in order to succeed. You are going to fail some quests. People are going to die. And Original Sin 2 really requires you to be on board with that, otherwise you're going to have a bad time. If you're a completionist that needs to clear an area completely before moving on, Original Sin 2 may not be for you – it's a game that needs you to go with the flow and accept the world is going to move on, with or without you. If the game had an alignment, it would be chaotic neutral – and that's fantastic.
This is a great game for RPG fans to get their teeth into: over 20 hours in, you'll notice the story only just starts gaining traction, and you may only just start getting familiar with the game's myriad systems. The game is unforgiving, often mercilessly so, but if you have the patience to penetrate the density and crack open the core gameplay, there's such a wealth of well-written RPG content, it's impossible not to recommend.

redpajama_set_name: RedPajamaCommonCrawl


text:
Q: React Native Android - using local gradle i cant download Gradle when i use the command " react-native run-android" i counter this error:

"Could not install the app on the device, read the error above for
  details. Make sure you have an Android emulator running or a device
  connected and have set up your Android development environment:
  https://facebook.github.io/react-native/docs/getting-started.html "

i want to use the local Gradle that i have downloaded manually
what should i do ?

redpajama_set_name: RedPajamaStackExchange