Thank you very much for inviting me. It's always lovely to talk to students because unlike when you're talking to faculty you guys listen
So it's it's always it's a polite audience and and you're not sitting on your laptop. So it's wonderful
I'm going to be talking about something a little different although not completely
Unconnected to the previous talk because actually I thought you were referring to heavy ion collisions when you were saying testable
We could have that discussion at the coffee break if you want
So what we do is basically melting that nuclei, and I'm going to explain a little bit more about what I mean by that
so as you guys know normal matter is made up of protons neutrons and
and electrons, and then they the protons and neutrons are themselves made up of quarks and gluons and
You guys have probably seen a picture similar to this I like the one with animals and I had to add my own higgs
By hand so I just went with a brontosaurus because by mass scale. That's roughly, right
But most of what I'm going to be talking to you guys about is
quarks and gluons because what we do is that we melt these nuclei and
Form what we now know is a liquid of quarks and gluons, and I'm going to be talking about others. What we directly measure is
hadrons, and there's different types, and they're all made up of quarks and gluons
There's a whole bunch of names you don't need to remember the names
Just that there's a lot of them, and you can think of them as analogous to
Two chemicals just like you can come up with different chemical compounds by different combinations of atoms you can come up with different
different hadrons by different combinations of quarks and antiquarks
So this is the phase diagram of nuclear matter and what I like about this phase diagram
Is that this is actually pretty close to
quantitative for what we knew when I started graduate school. We've gotten a little bit better
but
There's not much information on there, so the scale here is temperature in in
GEV which is very hot this is around a million times the the core of the sun
This temperature is very , this access is very oh chemical potential
Which is roughly the amount of energy that it needs to that you need to create
That you need to create a new baryon now
Here when you're here, what happens? Is that you're actually you have you have free energy in the system
So you're actually creating a baryon and an anti-baryon so you can create baryons
But your net number of baryons is not that high it is not increased
and
Up here we have what's called the course on plasma. Which we know isn't a liquid of quarks and gluons
about a million times hotter than the core of the sun
Normal Nuclear matter is down here basically on the axis on this scale and then these as you go to higher
Potentials it's been hypothesized that their stuff out here in neutral neutron Stars, but we can't directly access that experimentally, so
How do we get to these temperatures that are about a million times the core of the sun in the laboratory?
well
What you can't, what we'd like to do, you just heat it up
And then you have this little vat of QGP, and you can study it we can't really do that in practice
so what we do is that we compress Nuclei until
Until the Nucleon Boundary is irrelevant, and how we do that in the laboratory is that we take Nuclei
We strict strip them we take atoms
We stirred them strip them all all their electrons, and then we accelerate the Nuclei to very high speeds
smash them together they very briefly melt and then the system expands and cools
refreezing, so forming new hadron and
What we directly observe in our detector is these hadrons?
This is somewhat analogous to if you took two ice cubes in outer space got them going really fast
You sped them up smash them together. You would very briefly melt them and the system would expand and cool
You could determine the properties of water from looking at those ice shards as the system expands and cools
Hard but it would work
so what we actually have to do is figure out, how we
Infer the properties of matter from this of this melted nuclear matter from these frozen Shards of Nuclear matter
And I'm going to tell you a few different ways that we can do that
here are
You have in every high energy. Talk you have pictures like this these are the colliders
We can do this at this is the relativistic heavy ion, Collider on Long Island in New York
This is the large Hadron collider for scale. This is if you drew the
relativistic heavy Ion Collider on top of the LHC, this is
How large it would be the LHC is actually underground so you can't see it if you fly over
unlike RICK if you fly if you fly into JFK and get put in one of those annoying hold
Holding patterns sometimes you can actually you'll fly over long island and can see RICK or if you ever fly into islip airport
So I've done both word for contacts. Here's the Geneva airport
So here I've shown all the I've shown the different
Detectors that we have actually I see that some of them disappeared on my slide, and I need to edit my slide again
But what we can do here that we actually are able to
Move around on the phase diagram
so a lot of the things that you hear about
For particle physics they really just want to go to higher and higher energies because they want to create more and more massive particles
We're interested in moving around the entire phase diagram so that we can map it out
So rick is much more versatile
So it can cover
about
about an order of magnitude and Collision energy and
If you look in the this shows roughly the trajectories where we can move along on the phase diagram at RICK and the LHC
Has the highest energy collision so we can?
Get the hottest and most longest-lived quark-gluon Plasma. Which is what we call this liquid
so
Here are bigger pictures of the detectors that actually
That we actually use for scale, and I'm going to focus on this one
Which is the one that I do most of my work on
So here you can see the élysée detector. No high-energy
Talk is complete without a picture of a detector
And they kind of look the same if you haven't if you're they're not your detector
So here you can see for scale. This is the size of a person it is
It is huge. This is actually the this is a large Red Magnet and
this is one of those cases where it's
Convenient to be a small person because when you go in to work while the magnet doors are closed?
You have to climb through a hault hole that is this large
And that is fairly easy for me and not so easy for all of my collaborators
So it's a I have become much more appreciated for being small
You also have to scale the side of the detector to work on things and fix it which is
fun but very different skills and what you study in your classes in Grad school and
the whole purpose of all of this is that you're basically taking a picture of each of
the the collisions
so these collisions happen about a thousand times per second and
what you what you probably learn about in your classes is bubble Chambers and
Those happen slowly enough that you could actually see the particles move through the detector
But you can't do that when you have a thousand collisions per second so we have a bunch of different
Sub detectors and each of these have different purposes and one are trigger detectors
Those are basically those tell us when to take a picture when the collision actually happened and then tracking detectors
these are mostly sensitive to charged particles and
they tell us where the particles went so so far you can think of this as having basically a
Black and white camera a black-and-white picture that you know what you know that there was something there
And you know where it was but you can't tell what it was you. Can't tell colors very well
then we have
particle identification detectors that can tell us what type of particle it was and
calorimeters that tell us how much of energy how much energy had these I both think I think both of these is like giving the
Photograph color and the analogy does break down at some point, but it goes pretty far
so the the final product that we
That is actually what my students start with when they analyze data is something where they see the tracks
They're not actually dealing with the raw data. So here you can see an event display from a proton Proton Collision
It's only in two dimension
down the beam pipe here
And then it's in a magnetic field so you see the charge tracks curving these are calorimeter hits and the colors
Correspond to how much energy the particle has lost and heavier particles lose more energy in the detector than light particles
And this is all well and good
These collisions have on the order of about 50 tracks on average
Which is not too hard where it's not too hard to figure out which
Hits along the trajectory blunt to which particle. This is a central lead lead Collision where we have about
2,000 tracks
per Collision
And then the issue of tracking becomes very complicated
And we have because we have to be able to tease out all of the signals from all of these different particles
So that is in itself a very interesting computing
Problem not the one that I work on but I'm going to show you then a video of what this looks like I
Have learned through the years that you want to never be very careful about embedding effects into your
Talks because they often fail so and always test so okay, so this is outside of the powerpoint
so here you are moving along with the particle along the beam pipe, and there's another particle coming from the other direction and
they're about to Collide
they collide and
then the system expands and cools and here you can see all of the
all of the particles fly out and hit the detector and leave tracks in the detector as they do so
CERN is very good at PR So they give me lots of stuff to work with
and
We'll do it again because I think it takes a couple times to really absorb it so traveling along with the particle
They're about to Collide
They collide and the system expands and cools and they leave tracks and there's actually there are
Millions of channels of Data read out my experiment reads out
Terabytes per second
This poses all sorts of challenges that are very interesting
and
It's actually one of the most amazing things when you have
10,000 when you have millions of channels of detectors and several different sub detectors a
thousand collisions a second and
You know you have a lot of this actually built and tested by grad
Students, and you know you're often are put in roles where you don't really know what you're doing
The most amazing thing is that any of this works at all. I mean there's so many things that can go wrong
So it's it never ceases to be amazing to me that this actually works
So a few things of how I'm going to go through now when we have that data. How do we figure out?
What we're actually studying, so I'm going to go through a few different approaches
So one is QGP chemistry so I told you that we have all these different types of particles that we make
comprised of quarks and gluons
So what you can do is that you can measure you can just take a whole bunch of different particles
Count how many you have and look at the ratios of particles
Compared to a model, and this is just like in chemistry when you get different
numbers of molecules from different temperatures at equilibrium. We can actually use the ratios of particles to
to figure out what the temperature is so here you can see the red are the data points and the blue are a
Fit of a model to the data and what you get out of this fit is a chemical equilibrium
Temperature and we even see I won't go into the details what we see is that even strange quarks which are a little?
Heavier reach equilibrium, and you can do this for several different collision energies
And we go from this phase diagram that we had earlier
To what we actually have now where we can use this to actually map out where the this quark-Gluon plasma
freezes and we get something that we call a hadron gas so we're actually quantitatively mapping out the
phase diagram. Now that tells us what temperature the system was when
When the system froze out it doesn't tell us
What the highest temperatures we reached were and we're also interested in that
Yes, and we think there's a critical point here. So there's a whole program looking for that critical point
Which doesn't have inflow we have a partial answer. We think that it's somewhere in this range, but we're not quite sure we're
quantitatively
So what we really want is we want to know what the hottest temperatures. We reached were and
So how can we do that? I'm going to tell you about a few other
Ways that we can measure the temperature
and the first one is
Really cool. Well, they're all really cool
You guys have all heard of Blackbody radiation and I stole this picture off Wikipedia
And if you look at the distribution of photons emitted from some source you can use that to measure the temperature of the system
So what we do here is the black line
the sorry the dashed Line shows the
expectation for the production of photons from
Quantum chromodynamics in the absence of a plasma, so this is for the purpose of this measurement
this is the background and the
These points here show what we actually measure
For for photons that that are directly created in the collision
And you see that there is an excess above the QCD background and you can
There's now the whole system is expanding in and cooling so you
if you just look at the distribution of photons
You can't immediately say that that gives you the temperature you have to compare it to some model
So the raw inverse slope parameter
It corresponds to you get we call it an inverse slope parameter because it's not quite a temperature
But something around 200 MEV
But you compare this to models that can actually that have a lot of the behaviour in the in
Of the system in and you get that you have a temperature
Between four and six hundred MEV at the at the hottest point in the collision
so and this is of course been done both at the relativistic heavy ion Collider and
At the large Hadron Collider so the details are much more complicated, but the basic principle is
what you learn in Introductory Physics which is
Common theme I think in all subjects that you learn one of the other speakers mentioned it earlier
Too that these the core concepts in introductory physics are really important and stick with you for through your career
so the other approach is to
look at what melts. So we have states of corconia in this case
We call them bottomonium that this plot shows
This has both bottomonium and charmonia
Which is a bound state between a bottom quark and an anti bottom quark in between a charm quark and an anti-charm quark
and
by looking at so this is the ratio of
what was produced so we can actually calculate the number of produced theoretically to what we actually observe and
And what you see is that as you get to
looser and looser bound systems that
You're less likely to find them in the final state, so this is somewhat comparable to if you have
say
If you have a vat of some unknown metal
And you don't know how hot it is
you can drop stuff in it and
See if it melts so you throw an ice cube in it's going to melt but you throw a hunk of granite in
And it probably won't and so so you can get some
Constraints on the temperature by doing that by by just looking at what can actually survive in the system
so and this is a better plot to show that here you see the binding energy and
then here you see the number the ratio of the number we we
still have to the number we expect so one means nothing is melted and
We get again some temperature. There's a bunch of if you have stuff produced on the surface
It doesn't actually melt because it didn't interact so you never get quite to zero
But we again get a similar number that we think that the system gets to something like 604 to 600 MeV
at the highest energies
So that tells us a little bit more precisely that we start here and the system as it expands and cools
goes down like it follows a trajectory something like this until we it refreezes and then goes into the
into the pyon gas phase
So another one I want to talk about
because this is one of the things I did you can measure the energy density
Which is a little bit different from the temperature so back of the envelope
calculations
If the amount of energy you have in these collisions is actually not that much if you have a mosquito
Flying through the air one meter per second and it collides with another Mosquito
at 1 meter per second
That's about the amount of energy that you that you have in these collisions except that this is
concentrated in a very small volume of a few fermi Cubed
So that's why you can actually that's why you get these very high
Temperatures because you have very high energy densities, so you can approximate that
We don't have a precise way of calculating it
But what you do is that you treat the you figure out you calculate the rough volume of the system at its highest
At its highest temperature by basically treating saying okay, well it forms some rough Tube
That's the area of overlap between the Nuclei and then it took some time for the Nuclei to form the quark-Gluon plasma
so
Everything is traveling at Roughly the speed of light so this in this dimension
it's the time it took to form it over the speed of those times the speed of light and
Your energy density is basically the amount of energy you measure
divided by the total volume and
Here you can see the measurements that we have of the energy density
There's details. I'm fudging over asking me about them. If you're really interested
We expect the cork low on plasma forms at about
1
1 GeV per fermi Cubed and
What we get up to the relativistic heavy ion collider is about 6 and at the large Hadron Collider
It's a little over 12
So we get to something like 12 times the energy density that you need to form this matter, and we can measure it
That's that I think the one thing if you if you you don't want to remember?
I don't care if you remember what it is
but that actually by using Clever tricks and
working you know thinking of clever ways of doing it you can actually measure things that are really hard to measure and
The final thing I want to talk about is
analogous to
analogous to
UV visual spectroscopy, so what you ideally would do if you want to measure something that you you have no idea. What its properties are
you want to send a probe through the unknown medium and
so you know the properties of the probe before it goes through and then you measure how interactions with the medium change it and
a problem with this we can't just shine light into
Something that lives about 10 to the negative 23 seconds
So we have to figure out a clever way of doing it and what we do is that we use probes which were actually
created in the collision
And then what this is that this is what I work on we use something called Jets which
form when you have a quark or gluon on and one nucleus scatter off of a quark or gluon on in another nucleus and
because we expect this matter to be Roughly opaque to the
Took quarks and gluons we expect that quarks or gluons will travel through unscathed in
Contrast we have a built-in control as well that we expect this whole matter that all the course on plasma interacts through the strong force
but
We don't expect it to interact
Very well with I don't want to use strongly we don't expect it to
have significant interactions through the electromagnetic force, so
Electromagnetic probes we expect to just fly through unscathed, so that's a control which is another another nice thing
We're trying to measure something's really hard. We have a control so that we can make sure that we know what we're doing
The complication is that as you may know we don't see quarks or gluons directly?
we see their products and as they fly out they form these collimated sprays of
particles that are called Jet and
You don't have to worry about what they are just remember. They're Messy and hard
Really cool, so I professionally study messes
and
Here so we expect the picture that we expect is that we expect it when you have
the other nice thing about these jets is that they mostly form in pairs so again you have this built-in control because if you see
One you should have another which is by Momentum conservation
180 degrees away
so this was this plot was from the atlas collaboration and
This is along the beam pipe, and it's in a weird variable, but just this is along the beam pipe
And then 108 what you see is one jet here, and you see its partner 180 degrees away
And this has been a collision, which we say is peripheral. It was just glancing the two nuclei didn't interact very much and
What we see in a central collision. Is that actually you have?
That other particle absorbed
significantly, so one of the Jets disappears
now this is a lovely cartoon picture, but we actually we want to look at ways of
of
Quantifying things so I'm going to introduce the this observable called Raa
And again, this is this is I actually snuck it in and used it earlier. It's the
ratio of what you got to what you expect, so if you have
no, mod, and you can also do this by measuring something like proton-Proton collisions where we don't think we form this quark gluon plasma and
Comparing that to nucleus nucleus collisions. So anything above one is enhancement
you see more of what more than what you expected anything below is suppression and
this is some again analogous to
UV visual spectroscopy that you know a new Viva dual spectroscopy
You look at how many of something in this case. This is
This is actually yes, this is an absorption spectrum
And you can compare what you see to the pattern the pattern of different molecules to figure out what you had here again
We get a different type of spectrum
but we're looking at how much was absorbed and we can figure out the properties of the medium from that and
Here you see a whole lot of particles
the colors are
Each a different particle these the orange ones are electromagnetic probes, and we see they are consistent with one
so that's our control and
Everything else is a colored probe all sorts of different types of hadrons and we see
suppression of up to a factor of five as a relativistic heavy ion, Collider and
a factor of up to up to a factor of ten
That the large Hadron collider, so we see that this if this matter is actually opaque to colored probes
And we can actually do some pretty detailed
Theoretical calculations that I will not get into to quantify what the properties of this matter are from these measurements?
And I will skip over that
That last slide so take-home messages if you remember nothing else
when we
When we form these very high-energy nuclear when we do these high very high energy nuclear collision
We very briefly form a phase of matter called a quark Gluon plasma
and
This medium is incredibly hot and dense
And it is opaque to colored probes and translucent to electromagnetic probes
so we have lots of maybe the brief really brief metric message is we have lots of cool ways of measuring it and you just
Have to feet take what nature gives you and find the right way to use it
So a little bit about me
Here are the various degrees and positions? I do a lot on a lot of work on women in physics
I am working on being a more effective ally for
for people of color
Which is a very hard big and complicated problem. I am a parent
So here you can see my son
He's two and a half and I put this one in because this is actually his first gay pride parade
We were walking home from the farmers market and I have to say and there was the gay pride pride Parade
And it's good that these are much cleaner than they were a few decades ago. So everybody was
mostly closed
and he just remembers the octopus he wants to know one the man in the doctopus suit for whatever reason there was a man and
An Octopus he wants to know he's coming back
so
That is hard having kids and a career
I also have many hobbies, and I will tell you more about my bees, and you want to know
and
Things you can ask me about dealing with harassment. Which is very hard
Careers outside of physics which I have an explicit and explicably you become an expert on because lots of people talk to me about it
choosing a mentor and then managing this
Balance between having kids in the career. Thank you
