Accelerator Neutrinos

Abstract:

This article presents a measurement of the top quark mass using the CDF II detector at Fermilab. Colliding beams of protons and antiprotons at Fermilab's Tevatron (s=1.96TeV) produce top/antitop pairs, which decay to W+W-bb̄; events are selected where one W decays to hadrons and the other W decays to either e or μ plus a neutrino. The data sample corresponds to an integrated luminosity of approximately 318pb-1. A total of 165 tt̄ events are separated into four subsamples based on jet transverse energy thresholds and the number of b jets identified by reconstructing a displaced vertex. In each event, the reconstructed top quark invariant mass is determined by minimizing a χ2 for the overconstrained kinematic system. At the same time, the mass of the hadronically decaying W boson is measured in the same event sample. The observed W boson mass provides an in situ improvement in the determination of the hadronic jet energy scale. A simultaneous likelihood fit of the reconstructed top quark masses and the W boson invariant masses in the data sample to distributions from simulated signal and background events gives a top quark mass of 173.5-3.8+3.9GeV/c2. © 2006 The American Physical Society.

Abstract:

We report two measurements of the top-quark mass Mtop using the CDF II detector at the Fermilab Tevatron in a 318pb-1 data sample of tt̄ events in the lepton+jets final state. One method uses an event-based likelihood technique resulting in Mtop=173.2-2.4+2.6(stat)±3.2(syst)GeV/c2 or 173.2-4.0+4.1GeV/c2. The second method reconstructs a top-quark mass in each event using the measured invariant mass of the hadronically decaying W boson to constrain the jet energy scale to obtain a value for Mtop of 173.5-3.6+3.7(stat)±1.3(syst)GeV/c2 or 173.5-3.8+3.9GeV/c2. We take the latter, which is more precise, as our result. © 2006 The American Physical Society.