Measurement of the inclusive $$ \mathrm{t}\overline{\mathrm{t}} $$ cross section in pp collisions at $$ \sqrt{s}=5.02 $$ TeV using final states with at least one charged lepton

Abstract

Measurement of the inclusive tt cross section in pp collisions at √ s = 5.02 TeV using final states with at least one charged leptonThe CMS Collaboration * AbstractThe top quark pair production cross section (σ tt ) is measured for the first time in pp collisions at a center-of-mass energy of 5.02 TeV. The data were collected by the CMS experiment at the LHC and correspond to an integrated luminosity of 27.4 pb −1 . The measurement is performed by analyzing events with at least one charged lepton. The measured cross section is σ tt = 69.5 ± 6.1 (stat) ± 5.6 (syst) ± 1.6 (lumi) pb, with a total relative uncertainty of 12%. The result is in agreement with the expectation from the standard model. The impact of the presented measurement on the determination of the gluon distribution function is investigated.This analysis represents the first measurement of σ tt in pp collisions at √ s = 5.02 TeV using tt candidate events with +jets, where leptons are either electrons ( = e) or muons ( = µ), and dilepton (e ± µ ∓ or µ ± µ ∓ ) final states. In the former case, σ tt is extracted by a fit to the distribution of a kinematic variable for different categories of lepton flavor and jet multiplicity, while in the latter an event counting approach is used. The two results are then combined in the final measurement, which is used as input to a quantum chromodynamics (QCD) analysis at next-to-next-to-leading order (NNLO) to investigate the impact on the determination of the gluon distribution in the less-explored kinematic range of x 0.1. This paper is structured as follows. Section 2 describes the CMS detector. Section 3 gives a summary of the data and simulated samples used. After the discussion of the object reconstruction in Section 4, and of the trigger and event selection in Section 5, Section 6 describes the determination of the background sources. The systematic uncertainties are discussed in Section 7. The extraction of σ tt is presented in Section 8 and the impact of the presented measurement on the determination of the proton PDFs is discussed in Section 9. A summary of all the results is given in Section 10. The CMS detectorThe central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T parallel to the beam direction.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 composed of a barrel and two endcap sections. A preshower detector, consisting of two planes of silicon sensors interleaved with about 3 radiation lengths of lead, is located in front of the endcap regions of ECAL. Hadron forward calorimeters using steel as an absorber and quartz fibers as the sensitive material extend the pseudorapidity coverage provided by the barrel and endcap detectors from |η| = 3.0 to 5.2.Charged particle trajectories with |η| < 2.5 are measured by the tracker system, while the energy deposits in ECAL and HCAL cells are summed to ...

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