First Constraints on SU(5)xU(1) Supergravity from Trilepton Searches at the Tevatron

We present the first constraints on the parameter space of $SU(5)\times U(1)$ supergravity (in both no-scale and dilaton scenarios) which arise from the recently announced limits on trilepton searches at the Tevatron. The trilepton rate has been calculated for those points in parameter space which satisfy not only the minimal theoretical and experimental LEP constraints, but also the {\em combined} effect of the following indirect experimental constraints: (i) the CLEO limits on the $b\to s\gamma$ rate, (ii) the long-standing limit on the anomalous magnetic moment of the muon, (iii) the non-observation of anomalous muon fluxes in underground detectors (``neutrino telescopes"), and (iv) the electroweak LEP high-precision measurements in the form of the $\epsilon_{1},\epsilon_b$ parameters. For $m_t=150\GeV$, the trilepton constraint rules out some regions of parameter space with chargino masses as high as $m_{\chi^\pm_1}\approx105\GeV$, although it is not possible to establish a new absolute lower bound on the chargino mass. For $m_t=170\GeV$, the simultaneous imposition of {\em all} of the above constraints excludes the dilaton scenario completely, and leaves only a few allowed points in parameter space in the no-scale scenario (with $m_{\tilde q}\approx m_{\tilde g}\lsim285\GeV$). The five-fold increase in integrated luminosity expected in the upcoming Tevatron run should probe some regions of parameter space with chargino masses much beyond the reach of LEPII.