Precision measurement of the top quark mass in the lepton + jets channel using a matrix element method with Quasi-Monte Carlo integration

Abstract

This thesis presents a measurement of the top quark mass obtained from p$\bar{p}$ collisions at √s = 1.96 TeV at the Fermilab Tevatron using the CDF II detector. The measurement uses a matrix element integration method to calculate a t$\bar{t}$ likelihood, employing a Quasi-Monte Carlo integration, which enables us to take into account effects due to finite detector angular resolution and quark mass effects. We calculate a t$\bar{t}$ likelihood as a 2-D function of the top pole mass mt and ΔJES, where ΔJES parameterizes the uncertainty in our knowledge of the jet energy scale; it is a shift applied to all jet energies in units of the jet-dependent systematic error. By introducing ΔJES into the likelihood, we can use the information contained in W boson decays to constrain ΔJES and reduce error due to this uncertainty. We use a neural network discriminant to identify events likely to be background, and apply a cut on the peak value of individual event likelihoods to reduce the effect of badly reconstructed events. This measurement uses a total of 4.3 fb-1 of integrated luminosity, requiring events with a lepton, large ET, and exactly four high-energy jets in the pseudorapidity range |η| < 2.0, of which at least one must be tagged as coming from a b quark. In total, we observe 738 events before and 630 events after applying the likelihood cut, and measure mt = 172.6 ± 0.9 (stat.) ± 0.7 (JES) ± 1.1 (syst.) GeV/c2, or mt = 172.6 ± 1.6 (tot.) GeV/c2.