Dr Farrukh Azfar

Abstract:

We present new measurements of the inclusive forward-backward ttbar production asymmetry, AFB, and its dependence on several properties of the ttbar system. The measurements are performed with the full Tevatron data set recorded with the CDF II detector during ppbar collisions at sqrt(s) = 1.96 TeV, corresponding to an integrated luminosity of 9.4 fb^(-1). We measure the asymmetry using the rapidity difference Delta-y=y_(t)-y_(tbar). Parton-level results are derived, yielding an inclusive asymmetry of 0.164+/-0.047 (stat + syst). We observe a linear dependence of AFB on the top-quark pair mass M(ttbar) and the rapidity difference |Delta-y| at detector and parton levels. Assuming the standard model, the probabilities to observe the measured values or larger for the detector-level dependencies are 7.4*10^(-3) and 2.2*10^(-3) for M(ttbar) and |Delta-y| respectively. Lastly, we study the dependence of the asymmetry on the transverse momentum of the ttbar system at the detector level. These results are consistent with previous lower-precision measurements and provide additional quantification of the functional dependencies of the asymmetry.

Abstract:

A search is presented for the standard model Higgs boson produced in association with top quarks using the full Run II proton-antiproton collision data set, corresponding to 9.45fb-1, collected by the Collider Detector at Fermilab. No significant excess over the expected background is observed, and 95% credibility-level upper bounds are placed on the cross section σ(tt̄H→lepton+missing transverse energy+jets). For a Higgs boson mass of 125GeV/c2, we expect to set a limit of 12.6 and observe a limit of 20.5 times the standard model rate. This represents the most sensitive search for a standard model Higgs boson in this channel to date. © 2012 American Physical Society.

Abstract:

An inclusive search for the standard model Higgs boson using the four-lepton final state in proton-antiproton collisions produced by the Tevatron at √s=1.96TeV is conducted. The data are recorded by the CDF II detector and correspond to an integrated luminosity of 9.7fb -1. Three distinct Higgs decay modes, namely ZZ, WW, and ττ, are simultaneously probed. Nine potential signal events are selected and found to be consistent with the background expectation. We set a 95% credibility limit on the production cross section times the branching ratio and subsequent decay to the four-lepton final state for hypothetical Higgs boson masses between 120GeV/c2 and 300GeV/c2. © 2012 American Physical Society.

Abstract:

We report a measurement of the bottom-strange meson mixing phase βs using the time evolution of Bs0→J/ ψ(→μ+μ-)(→K+K-) decays in which the quark-flavor content of the bottom-strange meson is identified at production. This measurement uses the full data set of proton-antiproton collisions at √s=1.96TeV collected by the Collider Detector experiment at the Fermilab Tevatron, corresponding to 9.6fb -1 of integrated luminosity. We report confidence regions in the two-dimensional space of βs and the Bs0 decay-width difference ΔΓs and measure βs [-π/2,-1.51] [-0.06,0.30] [1.26,π/2] at the 68% confidence level, in agreement with the standard model expectation. Assuming the standard model value of βs, we also determine ΔΓs=0.068±0. 026(stat)±0.009(syst)ps-1 and the mean Bs0 lifetime τs=1.528±0.019(stat)±0.009(syst)ps, which are consistent and competitive with determinations by other experiments. © 2012 American Physical Society.