Professor Chris Hays

Abstract:

We present a measurement of the tt̄ production cross section using events with one charged lepton and jets from pp̄ collisions at a center-of-mass energy of 1.96 TeV. A b-tagging algorithm based on the probability of displaced tracks coming from the event interaction vertex is applied to identify b quarks from top decay. Using 318pb-1 of data collected with the CDF II detector, we measure the tt̄ production cross section in events with at least one restrictive (tight) b-tagged jet and obtain 8.9-1.0+1.0(stat)-1.0+1.1(syst)pb. The cross section value assumes a top quark mass of mt=178GeV/c2 in the acceptance corrections. The dependence of the cross section on mt is presented in the paper. This result is consistent with other CDF measurements of the tt̄ cross section using different samples and analysis techniques, and has similar systematic uncertainties. We have also performed consistency checks by using the b-tagging probability function to vary the signal-to-background ratio and also using events that have at least two b-tagged jets. © 2006 The American Physical Society.

Abstract:

We present the results of a search for new physics in the jets plus missing transverse energy data sample collected from 368 pb(-1) of pp collisions at square root of s = 1.96 TeV recorded by the Collider Detector at Fermilab. We compare the number of events observed in the data with a data-based estimate of the standard model backgrounds contributing to this signature. We observe no significant excess of events, and we interpret this null result in terms of lower limits on the fundamental Planck scale for a large extra dimensions scenario.

Abstract:

The DØ experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to DØ. © 2006 Elsevier B.V. All rights reserved.

Abstract:

We present a measurement of RB, the ratio of the branching fraction for the rare decay D0→K+π- to that for the Cabibbo-favored decay D0→K-π+. Charge-conjugate decays are implicitly included. A signal of 2005±104 events for the decay D0→K+π- is obtained using the CDF II detector at the Fermilab Tevatron collider. The data set corresponds to an integrated luminosity of 0.35fb-1 produced in p̄p collisions at s=1.96TeV. Assuming no mixing, we find RB=[4.05±0.21(stat)±0.11(syst)] ×10-3. This measurement is consistent with the world average, and comparable in accuracy with the best measurements from other experiments. © 2006 The American Physical Society.

Abstract:

We describe a measurement of the top quark mass using events with two charged leptons collected by the CDF II detector from pp̄ collisions with s=1.96TeV at the Fermilab Tevatron. The likelihood in top quark mass is calculated for each event by convoluting the leading order matrix element describing qq̄→tt̄→blνlb̄l′νl′ with detector resolution functions. The presence of background events in the data sample is modeled using similar calculations involving the matrix elements for major background processes. In a data sample with integrated luminosity of 340pb-1, we observe 33 candidate events and measure Mtop=165.2±6.1(stat.) ±3.4(syst.)GeV/c2. This measurement represents the first application of this method to events with two charged leptons and is the most precise single measurement of the top quark mass in this channel. © 2006 The American Physical Society.