Dr Farrukh Azfar

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.

Abstract:

We present the first observation and cross section measurement of exclusive dijet production in p̄p interactions, p̄p→p̄+dijet+p. Using a data sample of 310pb-1 collected by the Run II Collider Detector at Fermilab at s=1.96TeV, exclusive cross sections for events with two jets of transverse energy ETjet≥10GeV have been measured as a function of minimum ETjet. The exclusive signal is extracted from fits to data distributions based on Monte Carlo simulations of expected dijet signal and background shapes. The simulated background distribution shapes are checked in a study of a largely independent data sample of 200pb-1 of b-tagged jet events, where exclusive dijet production is expected to be suppressed by the Jz=0 total angular momentum selection rule. Results obtained are compared with theoretical expectations, and implications for exclusive Higgs boson production at the pp Large Hadron Collider at s=14TeV are discussed. © 2008 The American Physical Society.

Abstract:

We have performed a search for Bs0→μ+μ- and B0→μ+μ- decays in pp̄ collisions at s=1.96TeV using 2fb-1 of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron Collider. The observed number of Bs0 and B0 candidates is consistent with background expectations. The resulting upper limits on the branching fractions are B(Bs0→μ+μ-) <5.8×10-8 and B(B0→μ+μ-)<1.8×10-8 at 95% C.L. © 2008 The American Physical Society.

Abstract:

We search for evidence of resonant top quark pair production in 955 pb-1 of pp̄ collisions at s=1.96TeV recorded with the CDF II detector at the Fermilab Tevatron. For fully reconstructed candidate tt̄ events triggered on leptons with large transverse momentum and containing at least one identified b-quark jet, we compare the invariant mass spectrum of tt̄ pairs to the expected superposition of standard model tt̄, non-tt̄ backgrounds, and a simple resonance model based on a sequential Z′ boson. We establish upper limits for σ(pp̄→Z′) ·Br(Z′→tt̄) in the Z′ mass interval from 450GeV/c2 to 900GeV/c2. A topcolor leptophobic Z′ is ruled out below 720GeV/c2, and the cross section of any narrow Z′-like state decaying to tt̄ is found to be less than 0.64 pb at 95% C.L. for MZ′ above 700GeV/c2. © 2008 The American Physical Society.