Measurement of the top quark forward-backward production asymmetry and the anomalous chromoelectric and chromomagnetic m
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Received: December Revised: April Accepted: May Published: June
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The CMS collaboration E-mail: [email protected] Abstract: The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric (dˆt ) and chromomagnetic (ˆ µt ) moments have been measured using LHC pp collisions at a center-of-mass energy of 13 TeV, collected in the CMS detector in a data (1) sample corresponding to an integrated luminosity of 35.9 fb−1 . The linearized variable AFB is used to approximate the asymmetry. Candidate t¯t events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for t¯t (1) +0.020 final states. The values found for the parameters are AFB = 0.048+0.095 −0.087 (stat)−0.029 (syst), +0.016 ˆ µ ˆt = −0.024+0.013 −0.009 (stat)−0.011 (syst), and a limit is placed on the magnitude of |dt | < 0.03 at 95% confidence level. Keywords: Hadron-Hadron scattering (experiments), Top physics ArXiv ePrint: 1912.09540
Open Access, Copyright CERN, for the benefit of the CMS Collaboration. 3 Article funded by SCOAP .
https://doi.org/10.1007/JHEP06(2020)146
JHEP06(2020)146
Measurement of the top quark forward-backward production asymmetry and the anomalous chromoelectric and chromomagnetic moments in pp √ collisions at s = 13 TeV
Contents 1
2 Analysis strategy
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3 The CMS detector and physics objects
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4 Data and simulation
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5 Event reconstruction and selection
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6 Constructing templates and estimating background
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7 Systematic uncertainties
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8 Results
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9 Summary
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A Reweighting factors
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B Template binning
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The CMS collaboration
36
1
Introduction
The top quark (t) is the most massive of the known fundamental particles, with a mass (mt ) that is close to the electroweak scale. The Yukawa coupling of the top quark to the Higgs field is close to unity [1], which suggests that the top quark may play a role in electroweak symmetry breaking. The top quark is also the only color-triplet fermion that decays before forming color-singlet bound states. This provides a way to study its fundamental interactions with gauge bosons without the complications caused by hadronization. At the CERN LHC, according to the standard model (SM) of particle physics, top quarks are produced predominantly in pairs via the strong interaction, as described by quantum chromodynamics (QCD). Feynman diagrams for leading-order (LO) quarkantiquark (qq) and gluon-gluon (gg) initiated subprocesses are shown in figure 1(a), and example diagrams for next-to-leading-order (NLO) quark-gluon (qg) initiated subprocess are shown in figure 1(b). The NLO QCD calculations predict approximately 6% qq and 69% gg production of top quark pairs at a center-of-mass energy of 13 TeV.
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JHEP06(2020)146
1 Introduction
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