Dr Farrukh Azfar

Abstract:

This Letter describes the current most precise measurement of the $WZ$ production cross section as well as limits on anomalous $WWZ$ couplings at a center-of-mass energy of 1.96 TeV in proton-antiproton collisions for the Collider Detector at Fermilab (CDF). $WZ$ candidates are reconstructed from decays containing three charged leptons and missing energy from a neutrino, where the charged leptons are either electrons or muons. Using data collected by the CDF II detector (7.1 fb$^{-1}$ of integrated luminosity), 63 candidate events are observed with the expected background contributing $8 \pm 1$ events. The measured total cross section $\sigma (p \bar p \to WZ) = 3.93_{-0.53}^{+0.60}(\text{stat})_{-0.46}^{+0.59}(\text{syst}) $ pb is in good agreement with the standard model prediction of $3.50\pm 0.21$. The same sample is used to set limits on anomalous $WWZ$ couplings.

Abstract:

We report an indirect search for nonstandard model physics using the flavor-changing neutral current decays B→K(*) μ+μ-. We reconstruct the decays and measure their angular distributions, as a function of q2=Mμμ2c2, where M μμ is the dimuon mass, in pp̄ collisions at √s=1.96TeV using a data sample corresponding to an integrated luminosity of 6.8fb-1. The transverse polarization asymmetry AT(2) and the time-reversal-odd charge-and-parity asymmetry Aim are measured for the first time, together with the K* longitudinal polarization fraction FL and the muon forward-backward asymmetry AFB for the decays B0→K*0μ+μ- and B+→K*+μ+μ -. The B→K*μ+μ- forward-backward asymmetry in the most sensitive kinematic regime, 1≤q2<6GeV2/c2, is measured to be AFB=0.29-0.23+0.20(stat) ±0.07(syst), the most precise result to date. No deviations from the standard model predictions are observed. © 2012 American Physical Society.

Abstract:

We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7 - 5.4 fb^-1 of ppbar collisions collected during Run II of the Fermilab Tevatron Collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f0) and right-handed (f+) helicities, we find f0 = 0.722 \pm 0.081 [\pm 0.062 (stat.) \pm 0.052 (syst.)] and f+ = -0.033 \pm 0.046 [\pm 0.034 (stat.) \pm 0.031 (syst.)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f0 = 0.682 \pm 0.057 [\pm 0.035 (stat.) \pm 0.046 (syst.)] and f+ = -0.015\pm0.035 [\pm 0.018 (stat.) \pm 0.030 (syst.)]. The results are consistent with standard model expectations.

Abstract:

We have observed exclusive γγ production in proton-antiproton collisions at √s=1.96TeV, using data from 1.11±0.07fb-1 integrated luminosity taken by the Run II Collider Detector at Fermilab. We selected events with two electromagnetic showers, each with transverse energy ET>2.5GeV and pseudorapidity |η|<1.0, with no other particles detected in -7.4<η<+7.4. The two showers have similar E T and azimuthal angle separation Δψ∼π; 34 events have two charged particle tracks, consistent with the QED process pp̄→p+e+e-+p̄ by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive π0π0 is consistent with zero and is <15 at 95% C.L. The cross section for pp̄→p+γγ+p̄ with |η(γ)|<1.0 and ET(γ)>2.5GeV is 2.48-0.35+0.40(stat)-0.51+0.40(syst)pb. © 2012 American Physical Society.