Muon g-2 Constraints to SUSY Dark Matter over the Next Decade

Abstract

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.