Search for excited top quark pair production in lepton plus jets final state with √s = 13 TeV at CMS

• Main Authors: Yi-Mu Chen, 陳以牧
• Other Authors: 陳凱風
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/6h77kj

碩士 === 國立臺灣大學 === 物理學研究所 === 105 === This research searches for the pair production of spin-3/2 excited top quarks (t* t-*) in an extension of the Randall-Sundrum model with each excited t* decaying to a top quark and a gluon, using the data collected in 2016 with the CMS detector from pp collisions with a centre-of-mass energy of 13 TeV, and an integrated luminosity of 35.9 fb−1 . The search focuses on the semileptonic decay of the top quark pairs, with one top quarks decaying to a b quark plus two additional quarks from a hadronically decaying W boson, and the other top quark decaying to a b quark plus a lepton (muon or electron) and a neutrino from a leptonically decaying W boson. The observed final state of events that are selected for analysis requires an isolated muon or electron, an imbalance in transverse momentum, and at least six jets, two of which must be compatible with originating from the fragmentation of a b quark. The strategy of the analysis focuses on a kinematic reconstruction of t* objects, using the reconstruction mass as the discriminating variable for distinguishing between signal and background events. Extraction of potential signal events in data is obtained from an unbinned maximum likelihood fit of a signal-plus-background model to the observed mass spectrum. The data shows no significant excess over standard model predictions, and a lower limit of 1.2 TeV/c2 at 95% confidence level on the mass of the spin-3/2 t* quark model is set.