Measurements of $t\bar{t}$ spin correlations in CMS

TL;DR

This paper reports measurements of top-antitop quark spin correlations and polarization in proton-proton collisions at 7 TeV using CMS data, confirming Standard Model predictions and setting limits on the top-quark chromo-magnetic dipole moment.

Contribution

First analysis of $t\bar{t}$ spin correlations in CMS at 7 TeV using angular asymmetries and azimuthal angle differences, including limits on the top-quark chromo-magnetic dipole moment.

Findings

Results are consistent with Standard Model predictions.

Set limits on the real part of the top-quark chromo-magnetic dipole moment.

Measured angular asymmetries indicate unpolarized top quarks.

Abstract

We present an overview of the measurements of $t\bar{t}$ spin correlations in the CMS Collaboration. We present two analyses both in the dilepton channel using proton-proton collisions at $\sqrt{s}\, =\, 7$ TeV based on an integrated luminosity of 5.0 fb$^{-1}$. The spin correlations and polarization are measured using angular asymmetries. The results are consistent with unpolarized top quarks and Standard Model spin correlation. The second analysis sets a limit on the real part of the top-quark chromo-magnetic dipole moment of $-0.043\, <\, Re({\hat{\mu}}_{t})\, <\, 0.117$ at $95\,%$ confidence level through the measured azimuthal angle difference between the two charged leptons from $t\bar{t}$ production.