Professor Chris Hays

Abstract:

We present a measurement of the Bc+ meson lifetime in the decay mode Bc+ --> J/Psie+nue using the Collider Detector at Fermilab II detector at the Fermilab Tevatron Collider. From a sample of about of 360 pb(-1) of pp collisions at square root of s = 1.96 TeV, we reconstruct J/Psie+ pairs with invariant mass in the kinematically allowed range 4< M(J/Psie) < 6 GeV/c2. A fit to the decay-length distribution of 238 signal events yields a measured Bc+ meson lifetime of 0.463(-0.065)(+0.073)(stat) +/- 0.036(syst) ps.

Abstract:

We present results of a search for anomalous production of events containing a charged lepton (l, either e or mu) and a photon (gamma), both with high transverse momentum, accompanied by additional signatures X, including missing transverse energy (ET) and additional leptons and photons. We use the same selection criteria as in a previous CDF search but with a substantially larger data set, 305 pb(-1), a pp collision energy of 1.96 TeV, and the CDF II detector. We find 42 lgammaET events versus an expectation of 37.3+/-5.4 events. We observe 31 llgamma+X events versus an expectation of 23.0+/-2.7 events. We find no events similar to the run I eegammagammaET event.

Abstract:

We describe a measurement of the top quark mass from events produced in pp̄ collisions at a center-of-mass energy of 1.96 TeV, using the Collider Detector at Fermilab. We identify tt̄ candidates where both W bosons from the top quarks decay into leptons (eν, μν, or τν) from a data sample of 360pb-1. The top quark mass is reconstructed in each event separately by three different methods, which draw upon simulated distributions of the neutrino pseudorapidity, tt̄ longitudinal momentum, or neutrino azimuthal angle in order to extract probability distributions for the top quark mass. For each method, representative mass distributions, or templates, are constructed from simulated samples of signal and background events, and parametrized to form continuous probability density functions. A likelihood fit incorporating these parametrized templates is then performed on the data sample masses in order to derive a final top quark mass. Combining the three template methods, taking into account correlations in their statistical and systematic uncertainties, results in a top quark mass measurement of 170.1±6.0(stat.)±4.1(syst.) GeV/c2. © 2006 The American Physical Society.

Abstract:

We measure the branching fraction of the top quark to longitudinally and right-handed polarized W bosons, F0 and F+, using approximately 200pb-1 of p̄p collisions collected by the CDF II detector. We analyze two quantities sensitive to the W helicity: the invariant mass of the charged lepton and the bottom-quark jet in the decay t→Wb→ νb (where =e or μ), and the transverse momentum of the charged lepton. Constrained fits yield F0=0.74-0.34+0.22, and F+<0.27 at the 95% confidence level. These measurements are consistent with the standard model predictions. © 2006 The American Physical Society.

Abstract:

We report the first observation of Bs0→ψ(2S) decay in pp̄ collisions at s= 1.96 TeV using 360 pb-1 of data collected by the CDF II detector at the Fermilab Tevatron. We observe 20.2±5.0 and 12.3±4.1 Bs0→ψ(2S) candidates, in ψ(2S)→μ+μ- and ψ(2S)→J/ψπ+π- decay modes, respectively. We present a measurement of the relative branching fraction B(Bs0→ψ(2S) /B(Bs0→J/ψ)=0.52±0.13(stat)±0.04(syst)±0.06(BR) using the ψ(2S)→μ+μ- decay mode. © 2006 The American Physical Society.