Probing Supergravity Grand Unification in the Brookhaven g-2 Experiment

Abstract

A quantitative analysis of $\amu\equiv{1\over 2}(g-2)_\mu$ within the framework of Supergravity Grand Unification and radiative breaking of the electro-weak symmetry is given. It is found that $a_{\mu}^{SUSY}$ is dominated by the chiral interference term from the light chargino exchange, and that this term carries a signature which correlates strongly with the sign of $\mu$. Thus as a rule $a_{\mu}^{SUSY}>0$ for $\mu>0$ and $a_{\mu}^{SUSY}<0$ for $\mu<0$ with very few exceptions when tan$\beta\sim 1$. At the quantitative level it is shown that if the E821 BNL experiment can reach the expected sensitivity of $4\times 10^{-10}$ and there is a reduction in the hadronic error by a factor of four or more, then the experiment will explore a majority of the parameter space in $ m_0-m_{\tilde g}$ plane in the region $m_0\lsim 400$ GeV, $m_{\tilde g}\lsim 700$ GeV for $\tanbeta \gsim 10$ assuming the experiment will not discard the Standard Model result within its $2\sigma$ uncertainty limit. For smaller $\tanbeta$, the SUSY reach of E821 will still be considerable. Further, if no effect within $2 \sigma$ limit of the Standard Model value is seen, then large $\tanbeta$ scenarios will be severely constrained within the current naturalness criterion, ie., $m_0, m_{\tilde g}\lsim 1$ TeV.