Abstract
The cross section of top quark pair production is measured in the mathrm{t}overline{mathrm{t}}to left(ell {nu}_{ell}right)left({uptau}_{mathrm{h}}{nu}_{uptau}right)mathrm{b}overline{mathrm{b}} final state, where τh refers to the hadronic decays of the τ lepton, and ℓ is either an electron or a muon. The data sample corresponds to an integrated luminosity of 35.9 fb−1 collected in proton-proton collisions at sqrt{s} = 13 TeV with the CMS detector. The measured cross section is {sigma}_{mathrm{t}overline{mathrm{t}}} = 781 ± 7 (stat) ± 62 (syst) ± 20 (lumi) pb, and the ratio of the partial width Γ(t → τντb) to the total decay width of the top quark is measured to be 0.1050 ± 0.0009 (stat) ± 0.0071 (syst). This is the first measurement of the mathrm{t}overline{mathrm{t}} production cross section in proton-proton collisions at sqrt{s} = 13 TeV that explicitly includes τ leptons. The ratio of the cross sections in the ℓτh and ℓℓ final states yields a value {R}_{ell {uptau}_{mathrm{h}}/mathcal{ll}} = 0.973 ± 0.009 (stat) ± 0.066 (syst), consistent with lepton universality.
Highlights
Background estimateThe main background contribution comes from events with one lepton, significant pmTiss, and three or more jets, dominated by the lepton+jets tt process, where one of the jets is falsely identified as a τh
The event yields expected from the signal and background processes, as well as the observed event yields are summarized in table 1, for the signal-like and the background-like event categories in each of the eτh and μτh final states
The effect of the uncertainties on the signal strength is estimated by a likelihood scan where only one nuisance parameter is varied at once while the others are fixed to their nominal postfit values
Summary
The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter, and a brass and scintillator hadron calorimeter, each composed of a barrel and two endcap sections, covering 0 < φ < 2π in azimuth and |η| < 2.5 in pseudorapidity. Forward calorimeters extend the pseudorapidity coverage provided by the barrel and endcap detectors. The detector is nearly hermetic, providing reliable measurement of the momentum imbalance in the plane transverse to the beams. A more detailed description of the CMS detector, together with a definition of the coordinate system used and the relevant kinematic variables, can be found in ref. A more detailed description of the CMS detector, together with a definition of the coordinate system used and the relevant kinematic variables, can be found in ref. [16]
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