Measurements oftt¯Spin Correlations and Top-Quark Polarization Using Dilepton Final States inppCollisions at

S. Chatrchyan¹,

V. Khachatryan²,

A. M. Sirunyan³

et al.

Abstract

Spin correlations and polarization in the top quark-antiquark system are measured using dilepton final states produced in pp collisions at the LHC at sqrt[s]=7 TeV. The data correspond to an integrated luminosity of 5.0 fb(-1) collected with the CMS detector. The measurements are performed using events with two oppositely charged leptons (electrons or muons), a significant imbalance in transverse momentum, and two or more jets, where at least one of the jets is identified as originating from a b quark. The spin correlations and polarization are measured through asymmetries in angular distributions of the two selected leptons, unfolded to the parton level. All measurements are found to be in agreement with predictions of the standard model.

Simultaneous measurement of forward-backward asymmetry and top polarization in dilepton final states fromtt¯production at the Tevatron

“…Measurements of the polarization have been conducted for top pair production in pp collisions at the Large Hadron Collider at √ s = 7 TeV. These measurements, performed in different basis choices, are all consistent with the SM expectations [18,19].…”

Top-Quark Physics at the LHC

“…[116,117] and references in Ref. [121]. The angles θ ± require the explicit reconstruction of both the top quark and the antiquark, which is done using the AMWT technique.…”

“…The polarisation of top quarks in tt events is studied by CMS using the same data set and event selection as for the measurement of the tt spin correlation [121]. The polarisation is estimated from the unfolded distribution of the angle θ ± and the resulting asymmetry,…”

Measurements of the top quark properties in ttbar production at the LHC (includes charge asymmetry, top quark polarization, spin correlations and tt+V)

“…The CMS Collaboration has measured this observable using the dilepton decay channel in events collected at a collision energy of 7 TeV [15]. The measurement relies on the angle θ , which is defined as the angle between the top quark momentum in the tt rest frame and the momentum of the charged lepton in the top quark rest frame; this is referred to as the helicity basis for the polarization measurement.…”

“…This measurement [15] uses two different approaches to gain information on the spin correlations, unfolding the reconstructed distributions of two different sensitive variables. In both cases an asymmetry is calculated from the distributions as the final quantifier of the effect.…”