28,380 research outputs found
in supergravity models
We compute the supersymmetric contribution to
in a
variety of supergravity models. We find R^{\rm susy}_b\lsim0.0004, which does
not shift significantly the Standard Model prediction
( 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
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 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
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
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