Download or read book Measurement of the Cross Section of Top Quark Pairs Produced in Association with a Photon in Lepton + Jets Events at 8́(s written by Nabin Poudyal and published by . This book was released on 2021 with total page 259 pages. Available in PDF, EPUB and Kindle. Book excerpt: The inclusive production cross section of top quark pairs in association with a photon is measured in proton-proton collisions at the LHC with 13 TeV energy using the full RunII data collected by CMS in 2016, 2017, and 2018 with a total corresponding integrated luminosity of 137 fb 8́21 . The relative fraction of ttÎđ events normalized to inclusive tt production is measured. The cross section measurement provides important information about the electromagnetic coupling of the standard model top quark and is sensitive to physics beyond the standard model. The analysis is carried out in the in semileptonic decay channel with a well isolated high P T lepton (electron and muon), at least four jets out of which at least one must be b-tagged, and an isolated photon. Photons may be emitted from initial state radiation, top quarks, and decay products of top quarks. A simultaneous likelihood fit of control regions with the signal region is done to constraint the backgrounds and to extract the ttÎđ cross section. The measurement of the ratio of ttÎđ to tt is 0.02055 ℗ł 0.00099 (syst.) ℗ł 0.00099 (stat.) in the e + jets channel, 0.02156 ℗ł 0.00068 (syst.) ℗ł 0.00068 (stat.) in ℗æ + jets channel, and 0.02203 ℗ł 0.00064 (syst.) ℗ł 0.00064 (stat.) in the l + jets channel. The measured inclusive cross section is 3.81 ℗ł 0.15 (syst.) ℗ł 0.10 (stat.) pb in e + jets channel, 3.87 ℗ł 0.11 (syst.) ℗ł 0.07 (stat.) pb in ℗æ + jets channel, and 3.96 ℗ł 0.10 (syst.) ℗ł 0.06 (stat.) pb in l + jets channel for full RunII data. The results are in agreement with the standard model next to leading order prediction.