Measurement of multi-differential cross sections for the production of top quark pairs plus additional jets in pp collisions at √s = 13 TeV

Abstract

This thesis presents measurements of multi-differential top quark pair (ttbar) production cross-sections in pp collisions at the LHC with a center-of-mass energy of 13TeV using events containing two opposite-sign leptons. The analyzed dataset was recorded with the CMS detector in the years 2016, 2017, and 2018, and corresponds to an integrated luminosity of 137 fb−1. Precision double- and triple-differential cross-sections are measured as a function of observables describing the kinematic properties of the top quark, top antiquark, and t ̄t system, for both parton and particle level definitions of these objects. Furthermore, single- and double-differential cross-sections as functions of these observables are extracted in the presence of additional jets in the event. The set of results contains also the single differential cross-section of the number of additional jets for different ranges of minimum pT of the jets. Studies are also presented as function of the kinematics of the leading and sub-leading extra jets and the combined t ̄t plus leading extra jet system. The obtained unfolded cross-sections are compared to MC predictions based on Next-to-Leading order QCD matched to parton showers, and also to different beyond-NLO theory predictions. A study is performed on the possibility of using the double differential measurement as function of the top quark transverse momentum and t ̄t invariant mass as a two-dimensional reweighting of the t ̄t signal simulations at generator level, to improve the simulation. The effects of the application of such correction on different top and t ̄t system observables are analyzed.