  The anomalous magnetic moment of the muon has been measured to 0.5 ppm in a
series of precision experiments at the Brookhaven Alternating Gradient
Synchrotron. The individual results for each sign: a(mu+)= 11 659 204(7)(5)
E-10 and a(mu-) = 11 659 214(8)(3) E-10 are consistent with each other, so that
we can write the average anomaly as a(mu)(exp) = 11 659 208(6) E-10 (0.5 ppm).
A discrepancy between the measured value and the Standard Model (Delta a(mu))
is a signal for new physics. Assuming that such a discrepancy is due to
contributions from supersymmetric particles provides a framework which can be
used to constrain the mass of the dark matter particles, assumed to be the
lightest neutral supersymmetric particles. The deviation from the standard
model has varied between 1.5 sigma and 3 sigma significance, dominated by
uncertainties in the hadronic contribution to the standard model calculation.
Currently the standard model prediction is calculated to 0.6 ppm precision and
Delta a(mu) = 23.5 (9.0) E-10, representing a 2.6 sigma deviation. We expect
that the error on a(mu)(SM) will be reduced by a factor of two within the next
decade. To fully utilize this improvement, a new g-2 run is proposed for the
near future. If the mean Delta a(mu) remains the same, this would result in
close to a 6 sigma discrepancy. In this case, we would expect to see SUSY
particles at the LHC and use the g-2 results to measure tan beta. If, instead,
the Standard Model is confirmed to this precision, gauginos must have masses
higher than ~ 500 GeV/c2 and simple SUSY dark matter models will be severely
constrained.
