GLOBAL FITS OF THE SM AND MSSM TO ELECTROWEAK PRECISION DATA

A program including all radiative corrections to the Minimal Supersymm etric Standard Model (MSSM) at the same level as the radiative correct ions to the Standard Model (SM) has been developed and used to perform global fits to all electroweak data from LEP, SLC and the Tevatron an d the radiative b --> s gamma decay from CLEO. Values of the strong co upling constant at the M-Z scale and sin(2) theta(<(MS)over bar>) are derived, both in the SM and MSSM. Recent updates on electroweak data, which have been presented at the Warsaw Conference in summer 1996, red uce the too high branching ratio of the Z(0) boson into b-quarks in th e SM from a 3.2 sigma to a 1.8 sigma effect. In addition, the b --> s gamma decay is 30% below the SM prediction. In the MSSM light stops an d light charginos increase R-b and decrease the b --> s gamma rate, so both observations can be brought into agreement with the MSSM for the same region of parameter space. However, the resulting chi(2) value f or the MSSM fits is only marginally lower and in addition, the splitti ng in the stop sector has to be unnaturally high.