by AM Sirunyan · 2017 · Cited by 11 — Measurements of t¯t cross sections in association with b jets and usage of the uncertainty eigenvector sets of the PDF. The un-.
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PhysicsLettersB776(2018)355–378 Contentslistsavailableat ScienceDirect Physics Letters Bwww.elsevier.com/locate/physletb Measurements of t¯tcross sections in association with b jets and inclusive jets and their ratio using dilepton final states in pp collisions at s=13 TeV .The CMS Collaboration CERN, Switzerlanda r t i c l e i n f oa b s t r a c tArticle history: Received 29 May 2017Received in revised form 9 November 2017Accepted 21 November 2017Available online 23 November 2017Editor: M. DoserKeywords: CMSPhysics Top quark The cross sections for the production of t¯tb¯band t¯tjjevents and their ratio t¯tb¯b/t¯tjjare measured using data corresponding to an integrated luminosity of 2.3fb −1collected in pp collisions at s=13TeV with the CMS detector at the LHC. Events with two leptons (eor µ) and at least four reconstructed jets, including at least two identified as b quark jets, in the final state are selected. In the full phase space, the measured ratio is 0.022 ±0.003 (stat) ±0.006 (syst), the cross section t¯tb¯bis 4.0 ±0.6 (stat) ±1.3 (syst)pband t¯tjjis 184 ±6 (stat) ±33 (syst)pb. The measurements are compared with the standard model expectations obtained from apowhegsimulation at next-to-leading-order interfaced withpythia.2017 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/ ). Funded by SCOAP 3.1. Introduction Since the discovery of the Higgs boson[1–3], its properties have been measured and compared to the standard model (SM) predic- tion [4–9]. However, the coupling of the top quark to the Higgs boson remains to be determined. Although it appears indirectly through loops in the gluon–gluon fusion production process and in the H decay channel, a direct measurement has yet to be completed. One of the most promising channels for a direct measurement of the top quark Yukawa coupling in the SM is the production of the Higgs boson in association with a t¯tpair (t¯tH), where the Higgs boson decays to b¯b, thus leading to a t¯tb¯bfinal state. This final state, which has not been observed yet [10], has an irreducible nonresonant background from the production of a top quark pair in association with a b quark pair produced via gluon splitting (g b¯b). Calculations of the inclusive production cross section for t¯tevents with additional jets have been performed to next-to- leading-order (NLO) precision for proton–proton centre-of-mass energies of 7, 8, and 13TeV [11]. The dominant uncertainties in these calculations are from the choice of the factorization (µF) and renormalization (µR) scales[12,13], and are complicated by the presence of two very different scales in this process: the top quark mass and the jet transverse momentum (pT). Therefore, experi- E-mail address: cms-publication-committee-chair@cern.ch .mental measurements of production cross sections pp t¯tjj(t¯tjj)and pp t¯tb¯b(t¯tb¯b)can provide an important test of NLO quan- tum chromodynamics (QCD) theory calculations and important input for describing the main background in the search for the t¯tHprocess. Previous cross section and ratio measurements at s=7and 8TeVhave been reported by the CMS[14,15]and ATLAS Col-laborations [16].In this Letter, the measurements of the cross sections t¯tb¯band t¯tjjand their ratio are presented using a data sample of pp colli-sions collected at a centre-of-mass energy of 13TeVat the CERN LHC by the CMS experiment, and corresponding to an integrated luminosity of 2.3fb −1[17]. Events are selected with the final state consisting of two leptons (eor µ) and at least four reconstructed jets, of which at least two are identified as b quark jets. The cross section ratio is measured with a smaller systematic uncertainty ex- ploiting the partial cancellation of uncertainties.2. The CMS detector and event simulationThe central feature of the CMS apparatus is a superconduct- ing solenoid of 6m internal diameter, providing a magnetic field of 3.8T. Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each com-posed of a barrel and two endcap sections. Forward calorimeters extend the pseudorapidity () coverage provided by the barrel and https://doi.org/10.1016/j.physletb.2017.11.043 0370-2693/2017 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/ ). Funded by SCOAP 3.
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