Dr Farrukh Azfar

Abstract:

We present the results of a search for pair production of a new heavy toplike quark t′ decaying to a W boson and another quark using the Collider Detector at FermilabII detector in runII of the Tevatron pp̄ collider. Using a data sample corresponding to 760pb-1 of integrated luminosity, we fit the observed spectrum of total transverse energy and reconstructed t′ quark mass to a combination of standard model processes and t′ pair production. We see no evidence for t′t̄′ production, and we infer a lower limit of 256GeV/c2 on the mass of the t′ at 95% C.L. assuming standard strong couplings for the t′. © 2008 The American Physical Society.

Abstract:

This paper describes the first measurement of b-quark fragmentation fractions into bottom hadrons in Run II of the Tevatron Collider at Fermilab. The result is based on a 360pb-1 sample of data collected with the CDF II detector in pp̄ collisions at s=1.96TeV. Semileptonic decays of B̄0, B-, and B̄s0 mesons, as well as Λb0 baryons, are reconstructed. For an effective bottom hadron pT threshold of 7GeV/c, the fragmentation fractions are measured to be fu/fd=1.054±0.018(stat)-0.045+0.025(sys)±0. 058(B), fs/(fu+fd)=0.160±0.005(stat)-0.010+0.011(sys)-0.034+0.057(B), and fΛb/(fu+fd)=0.281±0.012(stat)-0.056+0.058(sys)-0.087+0.128(B), where the uncertainty B is due to uncertainties on measured branching ratios. The value of fs/(fu+fd) agrees within one standard deviation with previous CDF measurements and the world average of this quantity, which is dominated by LEP measurements. However, the ratio fΛb/(fu+fd) is approximately twice the value previously measured at LEP. The approximately 2σ discrepancy is examined in terms of kinematic differences between the two production environments. © 2008 The American Physical Society.

Abstract:

We measure the mean lifetime tau=2/(Gamma_{L}+Gamma_{H}) and the decay-width difference DeltaGamma=Gamma_{L}-Gamma_{H} of the light and heavy mass eigenstates of the B_{s}{0} meson, B_{sL}{0} and B_{sH}{0}, in B_{s}{0}-->J/psivarphi decays using 1.7 fb;{-1} of data collected with the CDF II detector at the Fermilab Tevatron pp[over ] collider. Assuming CP conservation, a good approximation for the B_{s}{0} system in the standard model, we obtain DeltaGamma=0.076_{-0.063}{+0.059}(stat)+/-0.006(syst) ps{-1} and tau=1.52+/-0.04(stat)+/-0.02(syst) ps, the most precise measurements to date. Our constraints on the weak phase and DeltaGamma are consistent with CP conservation.

Abstract:

We measure the time dependence of the ratio of decay rates for the rare decay D0→K+π- to the Cabibbo-favored decay D0→K-π+. A signal of 12.7×103 D0→K+π- decays was obtained using the Collider Detector at Fermilab II detector at the Fermilab Tevatron with an integrated luminosity of 1.5fb-1. We measure the D0-D̄0 mixing parameters (RD,y′,x′2) , and find that the data are inconsistent with the no-mixing hypothesis with a probability equivalent to 3.8 Gaussian standard deviations. © 2008 The American Physical Society.

Abstract:

We measure the mean lifetime τ=2/(ΓL+ΓH) and the decay-width difference ΔΓ=ΓL-ΓH of the light and heavy mass eigenstates of the Bs0 meson, BsL0 and BsH0, in Bs0→J/ψ decays using 1.7fb-1 of data collected with the CDF II detector at the Fermilab Tevatron pp̄ collider. Assuming CP conservation, a good approximation for the Bs0 system in the standard model, we obtain ΔΓ=0.076-0.063+0. 059(stat)±0.006(syst)ps-1 and τ=1.52±0.04(stat)±0. 02(syst)ps, the most precise measurements to date. Our constraints on the weak phase and ΔΓ are consistent with CP conservation. © 2008 The American Physical Society.