Measurement of the mass difference between top and anti-top quarks in pp collisions at √s = 7 TeV using the ATLAS detector

Abstract

A measurement of the mass difference between top and anti-top quarks is presented. In a 4.7 fb−1 data sample of proton–proton collisions at √s = 7 TeV recorded with the ATLAS detector at the LHC, events consistent with tt ̄ production and decay into a single charged lepton final state are reconstructed. For each event, the mass difference between the top and anti-top quark candidate is calculated. A two b-tag requirement is used in order to reduce the background contribution. A maximum likelihood fit to these per-event mass differences yields <math><mi mathvariant="normal" is="true">Δ</mi><mi is="true">m</mi><mo is="true">≡</mo><msub is="true"><mrow is="true"><mi is="true">m</mi></mrow><mrow is="true"><mi is="true">t</mi></mrow></msub><mo is="true">−</mo><msub is="true"><mrow is="true"><mi is="true">m</mi></mrow><mrow is="true"><mover accent="true" is="true"><mrow is="true"><mi is="true">t</mi></mrow><mrow is="true"><mo is="true">¯</mo></mrow></mover></mrow></msub><mo is="true">=</mo><mn is="true">0.67</mn><mo is="true">±</mo><mn is="true">0.61</mn><mspace width="0.2em" is="true"></mspace><mo stretchy="false" is="true">(</mo><mtext is="true">stat</mtext><mo stretchy="false" is="true">)</mo><mo is="true">±</mo><mn is="true">0.41</mn><mspace width="0.2em" is="true"></mspace><mo stretchy="false" is="true">(</mo><mtext is="true">syst</mtext><mo stretchy="false" is="true">)</mo><mtext is="true"> GeV</mtext></math>, consistent with CPT invariance.