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Measurement of the differential cross section of Z boson production in association with jets at the LHC

par Wang, Qun
Président du jury Mao, Yajun
Promoteur Favart, Laurent ;Ban, Yong
Publication Non publié, 2018-06-13

Thèse de doctorat

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Résumé :

This thesis presents the measurement of the differential cross section of Z boson pro-duction in association with jets (Z+jets) in proton-proton collision at the center-of-massenergy of 13 TeV. The data has been recorded with the CMS detector at the LHC duringthe year 2015, corresponding to an integrated luminosity of 2.19 fb −1 . A study of theCMS muon High Level Trigger (HLT) with the data collected in 2016 is also presented.The goal of analysis is to perform a first measurement at 13 TeV of the cross sections ofZ+jets as a function of the jet multiplicity, its dependence on the transverse momentumof the Z boson, the jet kinematic variables (transverse momentum and rapidity), thescalar sum of the jet momenta, and the balance in the transverse momentum betweenthe reconstructed jet recoil and the Z boson. The results are obtained by correctingthe detector effects, and are unfolded to particle level. The measurement are com-pared to four predictions using different approximations: at the leading-order (LO),next-to-leading-order (NLO) and next-to-next-to-leading order (NNLO) accuracy. Thefirst two calculations used M AD G RAPH 5_ A MC@NLO interfaced with PYTHIA 8 for theparton showering and hadronisation, one of which includes matrix elements (MEs) atLO, another includes one-loop corrections (NLO). The third is a fixed-order calculationwith NNLO accuracy for Z+1 jet using the N -jettiness subtraction scheme (N jetti ). Thefourth uses the GENEVA program with an NNLO calculation combined with higher-order resummation.A series of studies on the HLT double muon trigger are also included. Since 2015 theLHC reached higher luminosity, more events are produced inside the CMS detector persecond, which resulted in more challenges for the trigger system. The work presentedincludes the monitoring, validation and the calibration of the muon trigger paths since2016.