Abstract
Measurements are presented of the properties of top quarks in pair production and decay from proton-proton collisions at the LHC. The data were collected at centre-of-mass energies of 7 and 8 TeV by the CMS experiment during the years 2011 and 2012. The top quark-antiquark charge asymmetry is measured using the difference of the absolute rapidities of the reconstructed top and anti-top kinematics, as well as from distributions of the top quark decay products. The measurements are performed in the decay channels of the tt‾ pair into both one and two leptons in the final state. The polarization of top quarks and top pair spin correlations are measured from the angular distributions of top quark decay products. The W-boson helicity fractions and angular asymmetries are extracted and limits on anomalous contributions to the Wtb vertex are determined. The flavor content in top-quark pair events is measured using the fraction of top quarks decaying into a W-boson and a b-quark relative to all top quark decays, R=B(t→Wb)/B(t→Wq), and the result is used to determine the CKM matrix element Vtb as well as the width of the top quark resonance. All of the results are found to be in good agreement with standard model predictions.
Highlights
The top quark was discovered by the CDF and D0 collaborations in 1995 [1,2]
In the context of top pair production, the term charge asymmetry usually refers to a difference in the rapidity distributions of top quarks and anti-quarks
This final state offers better statistical precision than the dilepton analysis due to the larger hadronic branching ratio of the W boson decay, it suffers from larger backgrounds originating from W+jets and Quantum Chomodynamics (QCD) multijet events
Summary
The top quark was discovered by the CDF and D0 collaborations in 1995 [1,2]. Perhaps the most striking feature that sets the top quark apart from the other quarks is its very large mass. At 173.34 ± 0.76 GeV [3], it is approximately thirty times heavier than the heaviest bottom ( b) quark and is the heaviest elementary particle in the Standard Model (SM) Because of this fact, it is natural to ask whether the top quark plays a special role in the SM. Precise measurements of the properties of the top quark and its interactions may reveal effects from new physics. This concerns in particular the study of differential distributions, such as the asymmetry in the rapidity distributions of the top quark and anti-quark. The data used in the described measurements correspond to integrated luminosities of 5 fb-1 and 20 fb-1 at 7 and 8 TeV center-of-mass energies, respectively
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