Dr Farrukh Azfar

Abstract:

We present a search for new particles in an extension to the standard model that includes a heavy Higgs boson (H0), a lighter charged Higgs boson (H ±), and an even lighter Higgs boson h0, with decays leading to a W-boson pair and a bottom-antibottom quark pair in the final state. We use events with exactly one lepton, missing transverse momentum, and at least four jets in data corresponding to an integrated luminosity of 8.7 fb-1 collected by the CDF II detector in proton-antiproton collisions at √s=1.96 TeV. We find the data to be consistent with standard model predictions and report the results in terms of a simplified Higgs-cascade-decay model, setting 95% confidence level upper limits on the product of cross section and branching fraction from 1.3 pb to 15 fb as a function of H0 and H ± masses for mh0=126 GeV/c2. © 2013 American Physical Society.

Abstract:

This Letter reports a measurement of the cross section for producing pairs of central prompt isolated photons in proton-antiproton collisions at a total energy √s=1.96 TeV using data corresponding to 9.5 fb-1 integrated luminosity collected with the CDF II detector at the Fermilab Tevatron. The measured differential cross section is compared to three calculations derived from the theory of strong interactions. These include a prediction based on a leading order matrix element calculation merged with a parton shower model, a next-to-leading order calculation, and a next-to-next-to-leading order calculation. The first and last calculations reproduce most aspects of the data, thus showing the importance of higher-order contributions for understanding the theory of strong interaction and improving measurements of the Higgs boson and searches for new phenomena in diphoton final states. © 2013 American Physical Society.

Abstract:

We report a measurement of the time-dependent ratio of D0→K +π- to D0→K-π+ decay rates in D*+-tagged events using 1.0 fb-1 of integrated luminosity recorded by the LHCb experiment. We measure the mixing parameters x′2=(-0.9±1.3)×10-4, y′=(7.2±2.4)×10-3, and the ratio of doubly-Cabibbo-suppressed to Cabibbo-favored decay rates RD=(3. 52±0.15)×10-3, where the uncertainties include statistical and systematic sources. The result excludes the no-mixing hypothesis with a probability corresponding to 9.1 standard deviations and represents the first observation of D0-D̄0 oscillations from a single measurement. © 2013 CERN.

Abstract:

We measure the polarization of W bosons from top-quark (t) decays into final states with a charged lepton and jets, tt̄→W+bW -b̄→ℓνbqq̄′b̄, using the full Run II data set collected by the CDF II detector, corresponding to an integrated luminosity of 8.7 fb-1. A model-independent method simultaneously determines the fraction of longitudinal (f0) and right-handed (f+) W bosons to yield f0=0.726±0. 066(stat)±0.067(syst) and f+=-0.045±0.044(stat) ±0.058(syst) with a correlation coefficient of -0.69. Additional results are presented under various standard model assumptions. No significant discrepancies with the standard model are observed. © 2013 American Physical Society.

Abstract:

The first observation of the production of a W boson with a single charm quark (c) jet in pp̄ collisions at √s=1.96 TeV is reported. The analysis uses data corresponding to 4.3 fb-1, recorded with the CDF II detector at the Fermilab Tevatron. Charm quark candidates are selected through the identification of an electron or muon from charm-hadron semileptonic decay within a hadronic jet, and a Wc signal is observed with a significance of 5.7 standard deviations. The production cross section σ Wc(pTc>20 GeV/c,|ηc|<1.5) ×B(W→ℓν) is measured to be 13.6-3.1+3.4 pb and is in agreement with theoretical expectations. From this result the magnitude of the quark-mixing matrix element Vcs is derived, |Vcs|=1. 08±0.16 along with a lower limit of |Vcs|>0.71 at the 95% confidence level, assuming that the Wc production through c to s quark coupling is dominant. © 2013 American Physical Society.