Measurements of t t-bar spin correlations and top quark polarization using dilepton final states in pp collisions at sqrt(s) = 8 TeV

TL;DR

This paper reports measurements of top quark-antiquark spin correlations and polarization in proton-proton collisions at 8 TeV, using dilepton final states, and finds results consistent with the Standard Model while setting limits on possible new physics.

Contribution

First measurement of t t-bar spin correlations and polarization in dilepton final states at 8 TeV with unfolded parton-level results.

Findings

Results agree with Standard Model predictions.

No evidence of anomalous top quark chromo moments.

Set limits on chromo-magnetic and chromo-electric dipole moments.

Abstract

Measurements of the top quark-antiquark (t t-bar) spin correlations and the top quark polarization are presented for t t-bar pairs produced in pp collisions at sqrt(s) = 8 TeV. The data correspond to an integrated luminosity of 19.5 inverse femtobarns collected with the CMS detector at the LHC. The measurements are performed using events with two oppositely charged leptons (electrons or muons) and two or more jets, where at least one of the jets is identified as originating from a bottom quark. The spin correlations and polarization are measured from the angular distributions of the two selected leptons, both inclusively and differentially, with respect to the invariant mass, rapidity, and transverse momentum of the t t-bar system. The measurements are unfolded to the parton level and found to be in agreement with predictions of the standard model. A search for new physics in the form of anomalous top quark chromo moments is performed. No evidence of new physics is observed, and exclusion limits on the real part of the chromo-magnetic dipole moment and the imaginary part of the chromo-electric dipole moment are evaluated.