A measurement of the mass difference between the top quark and the antitop quark (Δmt = mt −m¯t ) is performed using events with a muon and at least four jets in the final state. Data collected in 2011 with the CMS detector at the LHC and corresponding to an integrated luminosity of 1.09
fb−1 are analyzed. The measured value of Δmt = −1.2 ± 1.2(stat.) ± 0.5(syst.) GeV is consistent with the Standard Model