Measurement of spin correlation between top and antitop quarks produced in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV

TL;DR

This paper reports a measurement of the spin correlation between top and antitop quarks produced in proton-antiproton collisions at 1.96 TeV, confirming the standard model prediction with significant statistical evidence.

Contribution

It introduces a matrix element technique applied to Tevatron data to measure top-antitop spin correlation, providing the first strong evidence for non-zero correlation at this energy.

Findings

Measured spin correlation coefficient $O_{off} = 0.89 \, extpm \, 0.22

Result agrees with standard model predictions

Provides 4.2 sigma evidence for non-zero spin correlation

Abstract

We present a measurement of the correlation between the spins of t and tbar quarks produced in proton-antiproton collisions at the Tevatron Collider at a center-of-mass energy of 1.96 TeV. We apply a matrix element technique to dilepton and single-lepton+jets final states in data accumulated with the D0 detector that correspond to an integrated luminosity of 9.7 fb$^{-1}$. The measured value of the correlation coefficient in the off-diagonal basis, $O_{off} = 0.89 \pm 0.22$ (stat + syst), is in agreement with the standard model prediction, and represents evidence for a top-antitop quark spin correlation difference from zero at a level of 4.2 standard deviations.