Accelerator Neutrinos

Abstract:

We report a measurement of the forward-backward charge asymmetry of electrons from W boson decays in pp̄ collisions at √s=1.96 TeV using a data sample of 170 pb^-1 collected by the Collider Detector at Fermilab. The asymmetry is measured as a function of electron rapidity and transverse energy and provides new input on the momentum fraction dependence of the u and d quark parton distribution functions within the proton. © 2005 The American Physical Society.

Abstract:

Using 180 pb ^-1 of data collected with the CDF II detector at the Tevatron, we measure the first two moments of the hadronic invariant mass-squared distribution in charmed semileptonic B decays. From these we determine the nonperturbative Heavy Quark Effective Theory parameters Λ and λ 1 used to relate the B meson semileptonic branching ratio to the CKM matrix element |V cb|. For a minimum lepton momentum of 0.7 GeV/c in the B rest frame we measure the first two moments of the D** → D ^(*)π component to be 〈m D** ²〉 = (5.83 ± 0.16 stat ± 0.08 syst) GeV ²/c ⁴ and 〈(m D** ² - 〈m D** ²〉) ²〉 = (1.30 ± 0.69 stat ± 0.22 syst) GeV ⁴/c ⁸. Combining these with the discrete mass terms from the D and D* mesons, we find the total moments to be 〈M Ξc ²〉 - m̄ D ² = (0.467 ± 0.038 stat ± 0.068 syst GeV ²/c ⁴ and 〈(M Ξc ² - 〈M Ξc ²〉) ²〉 = (1.05 ± 0.26 stat ± 0.13 syst) GeV ⁴/c ⁸, where m̄ D is the spin-averaged D mass. The systematic error is dominated by the uncertainties in the world-average branching ratios used to combine the D, D*, and D** contributions. The analysis makes no assumptions about the shape or resonant structure of the D** → D (*)π invariant mass distribution. © 2005 The American Physical Society.

Abstract:

We present a measurement of the tt̄ production cross section using events with one charged lepton and jets from pp̄ collisions at a center-of-mass energy of 1.96 TeV. In these events, heavy flavor quarks from top quark decay are identified with a secondary vertex tagging algorithm. From 162 pb^-1 of data collected by the Collider Detector at Fermilab, a total of 48 candidate events are selected, where 13.5 ± 1.8 events are expected from background contributions. We measure a tt̄ production cross section of 5.6-1.1^+1.2(stat.)-0.6^+0.9(syst.) pb. © 2005 The American Physical Society.

Abstract:

We present the results of a search for the flavor-changing neutral current decay Bs⁰ → μ⁺ μ^-. using a data set with integrated luminosity of 240 pb^-1 of pp̄ collisions at √s = 1.96 TeV collected with the D0 detector in run II of the Fermilab Tevatron collider. We find the upper limit on the branching fraction to be B(Bs⁰ → μ⁺ π^-) ≤ 5.0 × 10^-7 at the 95% C.L. assuming no contributions from the decay Bd⁰ → μ⁺ μ^- in the signal region. This limit is the most stringent upper bound on the branching fraction Bs⁰ → μ⁺ μ^- to date. © 2005 The American Physical Society.

Abstract:

Using the exclusive decay Bs⁰ → J/ψ (μ⁺μ^-)φ (K⁺K^-), we report the most precise single measurement of the Bs⁰ lifetime. The data sample corresponds to an integrated luminosity of approximately 220 pb^-1 collected with the DO detector at the Fermilab Tevatron Collider in 2002-2004. We reconstruct 337 signal candidates, from which we extract the Bs⁰ lifetime, τ(Bs⁰) = 1.444-0.090^+0.098(stat) ± 0.020(sys) ps. We also report a measurement for the lifetime of the B⁰ meson using the exclusive decay B⁰ → J/ψ(μ⁺μ^-) K*⁰(&92)(K⁺π^-). We reconstruct 1370 signal candidates, obtaining τ(B⁰) = 1.473 -0.050^+0.052(stat)±0.023(sys) ps, and the ratio of lifetimes, τ(Bs⁰)/τ(B⁰) = 0.980 -0.0.71^0.076(stat) ± 0.003(sys). © 2005 The American Physical Society.