Measurements of spin correlation in top-antitop quark events from proton-proton collisions at $\sqrt{s}=7$ TeV using the ATLAS detector

TL;DR

This paper reports measurements of spin correlations in top-antitop quark pairs produced in 7 TeV proton-proton collisions at the LHC, using ATLAS data, with some observables measured for the first time, confirming Standard Model predictions.

Contribution

It introduces new observables for measuring top quark spin correlation and provides the first measurements of some of these observables at the LHC.

Findings

Measurements agree with Standard Model predictions

Some observables are measured for the first time

Results support the Standard Model at NLO accuracy

Abstract

Measurements of spin correlation in top quark pair production are presented using data collected with the ATLAS detector at the LHC with proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 4.6 fb$^{-1}$. Events are selected in final states with two charged leptons and at least two jets and in final states with one charged lepton and at least four jets. Four different observables sensitive to different properties of the top quark pair production mechanism are used to extract the correlation between the top and antitop quark spins. Some of these observables are measured for the first time. The measurements are in good agreement with the Standard Model prediction at next-to-leading-order accuracy.