  The magnetic moment is a fundamental property of particles. The measurement
of these magnetic moments and the comparison with the values predicted by the
standard model of particle physics is a way to test our understanding of the
fundamental building blocks of our world. In some cases, such as for the
electron, this comparison has resulted in confirmation of the standard model
with incredible precision. In contrast, the magnetic moment of the muon has
shown a long-standing disagreement in the measured and the predicted value.
There is currently a tantalizing three-standard-deviation difference between
the current best measurement (with a precision of 0.54 ppm) and the
state-of-the-art standard model prediction. This represents one of the very few
experimental hints for physics beyond the standard model. There are currently
two major experimental efforts underway to improve the precision of the muon
magnetic moment measurement. The first is an evolution of the E-821 experiment,
originally located at Brookhaven National Laboratory in the United States. This
is experiment, E-989, is located at Fermilab and will measure the spin
precession rate of positive muons in a 14-m diameter storage ring using decay
positrons. The goal of the experiment is to reduce the current experimental
uncertainty by a factor of three. The experiment is currently being constructed
and aims to start taking data in 2017. An alternative, and very complementary,
experiment is being planned at J-PARC in Japan. This experiment, E-34, will
utilize low energy, ultra-cold muons in a much smaller storage ring. This
experiment aims for a similar precision to the Fermilab experiment and aims to
begin data taking on a similar timescale.

High Energy Physics - Experiment;Instrumentation and Detectors