Precision tests of the MSSM

Abstract

We present the results of a first global fit to the electroweak observables in the MSSM. The best fit selects either very low or very large values of ~$\tan \beta$ ~and, correspondingly, chargino (higgsino--like) and stop or the ~$CP-$odd Higgs boson are within the reach of LEP 2. Moreover, the best fit gives ~ ${\alpha }_s(M_Z)=0.118_{-0.010}^{+0.005}$, ~which is lower than the one obtained from the SM fits. The overall fit is excellent ~ (${\chi }^2=7.2$ ~for 15 d.o.f. as compared to ~${\chi }^2=11$ ~in the SM). Those results follow from the fact that in the MSSM one can increase the value of ~ $R_b\equiv {\Gamma }_{Z^0\to \bar{b}b}/{\Gamma }_{Z^0\to hadrons}$ ~ {\it without} modyfying the SM predictions for other observables.

Comments: 10 pages, LaTEX, 7 figures (not included) may be obtained from chank@fuw.edu.pl upon request. Modified version of the plenary talk given by S. Pokorski at the ``Beyond the Standard Model IV'', Lake Tahoe, CA, December 1994