[en] The semileptonic decay of a b quark, b→clν, is considered in the relativistic limit where the decay products are approximately collinear. Analytic results for the double differential lepton energy distributions are given for finite charm-quark mass. Their use for the fast simulation of isolated lepton backgrounds from heavy quark decays is discussed. (c) 2000 The American Physical Society

[en] This Letter describes a measurement of the muon cross section originating from b -quark decay in the forward rapidity range 2.4<| y^μ|<3. 2 in pp(bar sign) collisions at √(s)=1.8 TeV . The data used in this analysis were collected by the D0 experiment at the Fermilab Tevatron. We find that next-to-leading-order QCD calculations underestimate b -quark production by a factor of 4 in the forward rapidity region. (c) 2000 The American Physical Society

[en] We compute the α_s²β₀ part of the two-loop QCD corrections to the charged lepton spectrum in b→cscr(l)bar ν_scr(l) decays and find them to be about 50% of the first order corrections at all lepton energies, except those close to the end point. Including these corrections we extract the central values bar Λ=0.33 GeV and λ₁=-0.17 GeV² for the HQET matrix elements and use them to determine the MS b and c quark masses, and |V_cb|. copyright 1997 The American Physical Society

[en] We calculate the O(α_s²β₀) corrections to the decay rate b→c bar cs. For reasonable values of m_c/m_b this term is of the same order as both the one-loop and O(α_s²ln²m_W/m_b) corrections to the decay rate. For m_c/m_b=0.3 the O(α_s²β₀) corrections enhance the rate by ∼18% . We also discuss the O(α_s²β₀) corrections to b→cτ bar ν_τ, the B semileptonic branching fraction, and the charm multiplicity. copyright 1997 The American Physical Society

[en] We calculate the direct production rate of J/ψ in top quark decays. The color-octet J/ψ production via t→W⁺bJ/ψ is shown to have a large branching ratio of order 1.5x10^-4, which is over an order of magnitude higher than that of the color-singlet J/ψ production via t→W⁺bJ/ψgg or t→W⁺bχ_cJg followed by χ_cJ→J/ψγ. Our result can also be used as a tool to test the importance of the color-octet mechanism in heavy quarkonium production in the future. copyright 1997 The American Physical Society

[en] Within the minimal supersymmetric standard model we study the three body decay of the lighter top squark t₁→bWχ₁⁰ and compare this decay with the flavor-changing two body decay t₁→cχ₁⁰. Here χ₁⁰ is the lightest neutralino which we assume to be the lightest supersymmetric particle. We do this for scenarios where two body decays at the tree level are forbidden for the light top squark. We give the complete analysis for the three body decay and compare it with the mentioned two body decay. We discuss our numerical results in view of the upgraded Fermilab Tevatron, the CERN LHC, and a 500 GeV e⁺e^- Linear Collider. copyright 1997 The American Physical Society

[en] We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in 88 pb^-1 of pp collisions at √(s)=1.8 TeV . We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two b -quark jets. For a chargino mass of 90 GeV/c² and scalar neutrino masses of at least 40 GeV/c² , we find no evidence for scalar top production and present upper limits on the production cross section in both decay scenarios. (c) 2000 The American Physical Society

[en] We study both the branching ratio for b→sγ decay and the muon anomalous magnetic moment, a_μ≡(g-2)_μ/2, in the minimal supersymmetric standard model with gauge-mediated supersymmetry breaking. Combining new experimental data on a_μ and the branching ratio for b→sγ, strong limits on the parameter space of these models are derived. We find that this combined study leads to much stronger constraints on the parameter space of the model than those from either b→sγ or a_μ. In particular, the region of large tan β is extremely limited, which would have been otherwise allowed. We include the supersymmetric one-loop correction to the mass of b quark, m_b, and find that in order to have a correct value of m_b, the region of large tan β and μ<0 (in our convention) is not allowed in these models. The region of large tan β and μ>0 is also strongly constrained. We present bounds on supersymmetric particle masses as a function of tan β. (c) 2000 The American Physical Society

[en] We present the nonrelativistic QCD (NRQCD) prediction for the polarization of the J/ψ promptly produced in b→J/ψ+X, as well as the helicity-summed production rate. We propose that these observables can be of avail in measuring the three most important color-octet NRQCD matrix elements involved in J/ψ production. Anticipating the measurement of the polarization parameter α, we determine its expected range given current experimental bounds on the color-octet matrix elements. We find that the leading-order NRQCD prediction for the polarization parameter α is expected to lie in the range -0.33 to 0.05 whereas the color-singlet model prediction is -0.40±0.04. copyright 1997 The American Physical Society

[en] We investigate the implications of R-parity violation (RPV) for quark flavor violation both by constraining the sneutrino masses to be positive and by studying the processes b→sγ and K⁰-bar K⁰ mixing. In the latter there are two major contributions: one from open-quotes directclose quotes one loop diagrams involving RPV couplings, and one from the open-quotes indirectclose quotes contributions generated by the renormalization group. We compare the effects and discuss the implications of our results. copyright 1997 The American Physical Society