RbR_b in supergravity models

We compute the supersymmetric contribution to $R_{b}\equiv \Gamma (Z\to b{\bar b})/\Gamma (Z\to {\rm hadrons})$ in a variety of supergravity models. We find R^{\rm susy}_b\lsim0.0004, which does not shift significantly the Standard Model prediction ($R^{\rm SM}_b=0.2162$ for m_t=160\GeV). An improvement in experimental precision by a factor of four would be required to be sensitive to such an effect.Comment: 5 pages, LaTeX, 1 figure (included)

Heavy flavour production in the semi-muonic channel in pp and Pb-Pb collisions measured with the ALICE experiment

International audienceThe properties of the high-density medium formed in heavy-ion collisions at LHC can be investigated through heavy-quark production. These quarks are created in the initial hard collision processes with short formation time and are expected to lose energy while passing through the high-density strongly-interacting system. A complete understanding of heavy flavour production mechanisms in heavy-ion collisions requires the study of their production in proton-proton collisions. We will describe the ALICE muon spectrometer and then present the results on the production of single muons from heavy flavour decays at forward pseudo-rapidity (2.5 < eta < 4) in proton-proton collisions at s^1/2 = 7 TeV and Pb-Pb collisions at s^1/2_NN = 2.76 TeV. In particular, we will show the pt-differential production cross-section in proton-proton collisions and compare this to the perturbative QCD predictions as well as the nuclear modification factors R_AA and R_CP in Pb-Pb collisions

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.Comment: 9 pages, 5 figures, latex. Figures available as 0.540MB uuencoded file from [email protected]. CERN-TH.7107/93, CTP-TAMU-72/9