Professor Chris Hays

Abstract:

The tt̄ spin correlation at production is a fundamental prediction of QCD and a potentially incisive test of new physics coupled to top quarks. We measure the tt̄ spin state in pp̄ collisions at √s=1.96TeV using 1001 candidate events in the lepton plus jets decay channel reconstructed in the CDF II detector. In the helicity basis, for a top-quark mass of 172.5GeV/c2, we find a spin correlation coefficient κ=0.60±0.50(stat)±0. 16(syst), consistent with the QCD prediction, κ 0.40. © 2011 American Physical Society.

Abstract:

The collection of a large number of B-hadron decays to hadronic final states at the CDF II Detector is possible due to the presence of a trigger that selects events based on track impact parameters. However, the nature of the selection requirements of the trigger introduces a large bias in the observed proper-decay-time distribution. A lifetime measurement must correct for this bias, and the conventional approach has been to use a Monte Carlo simulation. The leading sources of systematic uncertainty in the conventional approach are due to differences between the data and the Monte Carlo simulation. In this paper, we present an analytic method for bias correction without using simulation, thereby removing any uncertainty due to the differences between data and simulation. This method is presented in the form of a measurement of the lifetime of the B- using the mode B-→D0π -. The B- lifetime is measured as τB -=1.663±0.023±0.015ps, where the first uncertainty is statistical and the second systematic. This new method results in a smaller systematic uncertainty in comparison to methods that use simulation to correct for the trigger bias. © 2011 American Physical Society.

Abstract:

We present a search for a new heavy charged vector boson W′ decaying to an electron-neutrino pair in pp̄ collisions at a center-of-mass energy of 1.96 TeV. The data were collected with the CDF II detector and correspond to an integrated luminosity of 5.3fb-1. No significant excess above the standard model expectation is observed and we set upper limits on σ•B(W′→eν). Assuming standard model couplings to fermions and the neutrino from the W′ boson decay to be light, we exclude a W′ boson with mass less than 1.12TeV/c2 at the 95% confidence level. © 2011 American Physical Society.

Abstract:

We report on a search for new particles in the diphoton channel using a data sample of pp̄ collisions at √s=1.96TeV collected by the CDF II detector at the Fermilab Tevatron, with an integrated luminosity of 5.4fb⊃-1. The diphoton invariant mass spectrum of the data agrees well with the standard model expectation. We set upper limits on the production cross section times branching ratio for the Randall-Sundrum graviton, as a function of diphoton mass. We subsequently derive lower limits on the graviton mass of 459GeV/c2 and 963GeV/c2, at the 95% confidence level, for coupling parameters (k/M̄Pl) of 0.01 and 0.1, respectively. © 2011 American Physical Society.