Direct measurement of the mass difference between top and antitop quarks

TL;DR

This paper reports a direct measurement of the mass difference between top and antitop quarks using the matrix element method on proton-antiproton collision data, finding no significant difference and confirming the standard model.

Contribution

First direct measurement of the top-antitop mass difference using the matrix element method in lepton+jets channels.

Findings

Mass difference dm = 0.8 +/- 1.8 (stat) +/- 0.5 (syst) GeV

Results consistent with no mass difference as predicted by the standard model

Analysis based on 3.6 fb-1 of proton-antiproton collision data

Abstract

We present a direct measurement of the mass difference between top and antitop quarks (dm) in lepton+jets top-antitop final states using the "matrix element" method. The purity of the lepton+jets sample is enhanced for top-antitop events by identifying at least one of the jet as originating from a b quark. The analyzed data correspond to 3.6 fb-1 of proton-antiproton collisions at 1.96 TeV acquired by D0 in Run II of the Fermilab Tevatron Collider. The combination of the e+jets and mu+jets channels yields dm = 0.8 +/- 1.8 (stat) +/- 0.5 (syst) GeV, which is in agreement with the standard model expectation of no mass difference.