Evidence for production of single top quarks and first direct measurement of
Physical Review Letters 98:18 (2007)
Abstract:
The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron pp̄ collider. Using a 0.9fb-1 dataset, we apply a multivariate analysis to separate signal from background and measure σ(pp̄→tb+X,tqb+X)=4.9±1.4pb. The probability to measure a cross section at this value or higher in the absence of a signal is 0.035%, corresponding to a 3.4 standard deviation significance. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa matrix element that describes the Wtb coupling and find 0.68<|Vtb|≤1 at 95% C.L. within the standard model. © 2007 The American Physical Society.Measurement of the charge asymmetry in semileptonic Bs0 decays.
Phys Rev Lett 98:15 (2007) 151801
Abstract:
We have performed the first direct measurement of the time-integrated flavor untagged charge asymmetry in semileptonic Bs0 decays ASLs,unt by comparing the decay rate of Bs0-->micro+Ds-nuX, where Ds- -->phipi- and phi-->K+K-, with the charge-conjugate Bs0 decay rate. This sample was selected from 1.3 fb-1 of data collected by the D0 experiment in run II of the Fermilab Tevatron collider. We obtain ASLs,unt=[1.23+/-0.97(stat)+/-0.17(syst)]x10(-2). Assuming that Deltam(s)/Gamma(s)>>1, this result can be translated into a measurement of the CP-violating phase in Bs0 mixing: DeltaGamma(s)/Deltam(s)tanphi(s)=[2.45+/-1.93(stat)+/-0.35(syst)]x10(-2).Measurement of the charge asymmetry in semileptonic Bs0 decays
Physical Review Letters 98:15 (2007)
Abstract:
We have performed the first direct measurement of the time-integrated flavor untagged charge asymmetry in semileptonic Bs0 decays ASLs,unt by comparing the decay rate of Bs0→μ+Ds-νX, where Ds- π- and →K+K-, with the charge-conjugate B̄s0 decay rate. This sample was selected from 1.3fb-1 of data collected by the D0 experiment in run II of the Fermilab Tevatron collider. We obtain ASLs,unt=[1.23±0.97(stat)±0. 17(syst)]×10-2. Assuming that Δms/Γ̄s 1, this result can be translated into a measurement of the CP-violating phase in Bs0 mixing: ΔΓs/Δmstan s=[2.45±1.93(stat)±0.35(syst)] ×10-2. © 2007 The American Physical Society.Search for single production of scalar leptoquarks in p over(p, ̄) collisions decaying into muons and quarks with the D0 detector
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 647:2-3 (2007) 74-81
Abstract:
We report on a search for second generation leptoquarks (LQ2) which decay into a muon plus quark in p over(p, ̄) collisions at a center-of-mass energy of sqrt(s) = 1.96 TeV in the D0 detector using an integrated luminosity of about 300 pb-1. No evidence for a leptoquark signal is observed and an upper bound on the product of the cross section for single leptoquark production times branching fraction β into a quark and a muon was determined for second generation scalar leptoquarks as a function of the leptoquark mass. This result has been combined with a previously published D0 search for leptoquark pair production to obtain leptoquark mass limits as a function of the leptoquark-muon-quark coupling, λ. Assuming λ = 1, lower limits on the mass of a second generation scalar leptoquark coupling to a u quark and a muon are mLQ2 > 274 GeV and mLQ2 > 226 GeV for β = 1 and β = 1 / 2, respectively. © 2007 Elsevier B.V. All rights reserved.Lifetime difference and CP-violating phase in the Bs0 system.
Phys Rev Lett 98:12 (2007) 121801