Measurement of the mass difference between $t$ and $\bar{t}$ quarks

TL;DR

This paper reports the most precise direct measurement to date of the mass difference between top quarks and anti-top quarks, using data from the Fermilab Tevatron collider, and finds a result slightly deviating from CPT symmetry.

Contribution

It introduces a novel event-by-event estimation method for measuring the top-antitop mass difference using lepton+jets events at the Tevatron.

Findings

Measured mass difference: -3.3 ± 1.4(stat) ± 1.0(syst) GeV/c^2

Result is approximately two standard deviations from zero

Most precise measurement of top-antitop mass difference to date

Abstract

We present a direct measurement of the mass difference between $t$ and $\bar{t}$ quarks using $\ttbar$ candidate events in the lepton+jets channel, collected with the CDF II detector at Fermilab's 1.96 TeV Tevatron \ppbar Collider. We make an event by event estimate of the mass difference to construct templates for top quark pair signal events and background events. The resulting mass difference distribution of data is compared to templates of signals and background using a maximum likelihood fit. From a sample corresponding to an integrated luminosity of \invfb{5.6}, we measure a mass difference, $\dmt = \mathrm{M}_{t} - \mathrm{M}_{\bar{t}} = -3.3 \pm 1.4(stat) \pm 1.0(syst)}$, approximately two standard deviations away from the CPT hypothesis of zero mass difference. This is the most precise measurement of a mass difference between $t$ and its $\bar{t}$ partner to date.