Search for pair production of a heavy quark decaying to top quark and photon in semi-leptonic channel with the CMS detector in the LHC

Using the data collected by the CMS detector in 2012, corresponding to aluminosity of 19.7 / fb of proton-proton collisions at LHC center-of-massenergy of 8 TeV, we search for the excited top quark, T*. The decayprocess and the final states studied in our analysis are: T* T*bar -> t γtbar γ -> b W+ γ bbar W- γ, where one W boson decays hadronically andthe other leptonically, so we define a signal region by requesting eventswith 2 photons, 1 lepton and >= 4jets. To reconstruct the invariant massof T*, a χ2-sorting method is used and 12 events are observed in thesignal region from data. The matrix method is used to estimate thebackground contribution among the observed 12 events in the di-photonchannel. As a result of this study, no significant excess is observed overexpectations and a lower limit is set on a t* quark mass of 969 GeV/c2 at95% confidence level.中文提要感謝Contents