Constraints on the top quark's charge with the CMS experiment

The standard model of particle physics is being probed at the LHC collider ring at Geneva.Amongst others, top-quark pairs are produced in large quantities. This makes precisionmeasurements of top-quark properties possible.The top quark as the electroweak-isospin partner of the bottom quark is expected to havean electric charge of +2/3 e. A measurement is presented that discriminates betweenthe top quark charge hypotheses of +2/3 e and −4/3 e using the muon+jets final stateof top-pair events tt → (bµν )(bqq ). The measurement is performed with proton-proton√collisions at s = 7 TeV recorded by the CMS detector in the year 2011, correspondingto an integrated luminosity of 5.0 fb−1 .Charge correlations between the high-pT muons from the hard process and a muon fromone of the bottom quarks are exploited to sort the events in a +2/3 e or −4/3 e category.The normalized asymmetry between both categories is calculated. The top quark chargescenario of −4/3 e would correspond to an asymmetry of A = −1. This is excluded withhigh significance while the measured asymmetry of A = 1.10 ± 0.12(stat.) ± 0.34(sys.)confirms the standard-model expectation of A = +1.