S. Wilbur

Search for the Decays B{sub (s)}{sup 0}{yields}e{sup +}{mu}{sup -} and B{sub (s)}{sup 0}{yields}e{sup +}e{sup -} in CDF Run II

We report results from a search for the lepton flavor violating decays B{sub s}{sup 0}{yields}e{sup +}{mu}{sup -} and B{sup 0}{yields}e{sup +}{mu}{sup -}, and the flavor-changing neutral-current decays B{sub s}{sup 0}{yields}e{sup +}e{sup -} and B{sup 0}{yields}e{sup +}e{sup -}. The analysis uses data corresponding to 2 fb{sup -1} of integrated luminosity of pp collisions at {radical}(s)=1.96 TeV collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron. The observed number of B{sup 0} and B{sub s}{sup 0} candidates is consistent with background expectations. The resulting Bayesian upper limits on the branching ratios at 90% credibility level are B(B{sub s}{sup 0}{yields}e{sup +}{mu}{sup -}) 47.8 TeV/c{sup 2}, and M{sub LQ}(B{sup 0}{yields}e{sup +}{mu}{sup -})>59.3 TeV/c{sup 2}, at 90% credibility level.

First Measurement of the tt Differential Cross Section d{sigma}/dM{sub tt} in pp Collisions at {radical}(s)=1.96 TeV

We present a measurement of the tt[over ] differential cross section with respect to the tt[over ] invariant mass, dsigma/dM_{tt[over ]}, in pp[over ] collisions at sqrt[s]=1.96 TeV using an integrated luminosity of 2.7 fb;{-1} collected by the CDF II experiment. The tt[over ] invariant mass spectrum is sensitive to a variety of exotic particles decaying into tt[over ] pairs. The result is consistent with the standard model expectation, as modeled by PYTHIA with CTEQ5L parton distribution functions.

First measurement of the ratio of branching fractions B({lambda}{sub b}{sup 0}{yields}{lambda}{sub c}{sup +}{mu}{sup -}{nu}{sub {mu}})/B({lambda}{sub b}{sup 0}{yields}{lambda}{sub c}{sup +}{pi}{sup -})

This article presents the first measurement of the ratio of branching fractions B(Λ 0 b → Λ + c μ - v μ )/B(Λ 0 b → Λ + c π - ). Measurements in two control samples using the same technique β(B 0 → D + μ - v μ )/B(B 0 → D + π - ) and B(B 0 → D*(2010) + μ-V μ )/B(B 0 → D*(2010) + π - ) are also reported. The analysis uses data from an integrated luminosity of approximately 172 pb -1 of pp collisions at √s = 1.96 TeV, collected with the CDF II detector at the Fermilab Tevatron. The relative branching fractions are measured to be B(Λ 0 b →Λ + cμ - v μ )-B(Λ 0 b Λ + c π - ) = 16.6 ± 3.0(stat) ± 1.0(syst) +2.6 -3.4 (PDG) ± 0.3(EBR), B(B 0 →D + μ - v μ )-B(B 0 →D + π - ) = 9.9 ± 1.0(stat) ± 0.6(syst) ± 0.4(PDG) ± 0.5(EBR), and B(B 0 →D*(2010)+μ - v μ )-B(d 0 →D*(2010) + π - ) =16.5 ± 2.3(stat) ± 0.6(syst) ± 0.5(PDG) ± 0.8(EBR). The uncertainties are from statistics (stat), internal systematics (syst), world averages of measurements published by the Particle Data Group or subsidiary measurements in this analysis (PDG), and unmeasured branching fractions estimated from theory (EBR), respectively. This article also presents measurements of the branching fractions of four new Λ 0 b semileptonic decays: Λ 0 b → Λ c (2595) + μ - v μ , Λ 0 b → Λ c (2625) + μ - v μ , Λ 0 b → Σ c (2455) 0 π + μ - v μ , and Λ 0 b → Σ c (2455) ++ π - μ - v μ , relative to the branching fraction of the Λ 0 b → Λ + c μ - v μ decay. Finally, the transverse-momentum distribution of Λ 0 b baryons produced in pp collisions is measured and found to be significantly different from that of B 0 mesons, which results in a modification in the production cross-section ratio σΛ 0 b /σB0with respect to the CDF I measurement.

Search for new physics in the {mu}{mu}+e/{mu}+Ee{sub T} channel with a low-p{sub T} lepton threshold at the Collider Detector at Fermilab

A search for new physics using three-lepton (trilepton) data collected with the CDF II detector and corresponding to an integrated luminosity of 976 pb(-1) is presented. The standard model predicts a low rate of trilepton events, which makes some supersymmetric processes, such as chargino-neutralino production, measurable in this channel. The mu mu + l signature is investigated, where l is an electron or a muon, with the additional requirement of large missing transverse energy. In this analysis, the lepton transverse momenta with respect to the beam direction (p(T)) are as low as 5 GeV/c, a selection that improves the sensitivity to particles that are light as well as to ones that result in leptonically decaying tau leptons. At the same time, this low-p(T) selection presents additional challenges due to the non-negligible heavy-quark background at low lepton momenta. This background is measured with an innovative technique using experimental data. Several dimuon and trilepton control regions are investigated, and good agreement between experimental results and standard-model predictions is observed. In the signal region, we observe one three-muon event and expect 0.4 +/- 0.1 mu mu + l events from standard-model processes.