Measurement of the top quark mass with in situ jet energy scale calibration using hadronic W boson decays at CDF-II

Abstract

We report a measurement of the top quark mass with the upgraded Collider Detector at Fermilab (CDF-II). The top quarks are produced in pairs ( tt¯) in proton-antiproton collisions with a center-of-mass energy of 1.96 TeV. Each top quark decays to a W boson and a bottom quark. We select candidate events in which one W boson decays hadronically and the other decays to an electron or a muon and its associated neutrino. The data sample, which corresponds to an integrated luminosity of 318 pb^-1, contains 138 tt¯ candidates. A top quark mass is reconstructed for each event by placing energy and momentum constraints on the top quark pair decay products. We also employ the reconstructed mass of the hadronic W boson decays W → jj to constrain in situ the largest systematic uncertainty of the top quark mass measurement, the jet energy scale. Monte Carlo templates of the reconstructed top quark and W boson mass are produced as a function of the top quark mass and the jet energy scale. The distribution of reconstructed top quark and W boson mass in the data are compared to the Monte Carlo templates using a likelihood fit to obtain M_top = [special characters omitted] GeV/c². This constitutes the most precise measurement of the top quark mass to date. This measurement can be used to constrain the mass of the Higgs boson, a central particle in the Standard Model of particle physics that has yet to be observed. We also demonstrate that this new technique reduces naturally the jet, energy scale uncertainty as more data is accumulated and thus provides the capability to measure M_top with an uncertainty of 2 GeV/c² or better by the end of the CDF-II experiment.