Measurement of the W boson helicity in events with a single reconstructed top quark in pp collisions at sqrt(s) = 8 TeV

TL;DR

This paper measures the helicity fractions of W bosons from top quark decays in proton-proton collisions at 8 TeV, providing insights into top quark properties and testing the Standard Model predictions.

Contribution

It presents the first measurement of W boson helicity fractions in single top quark events at 8 TeV, with improved precision and limits on anomalous couplings.

Findings

Measured helicity fractions: F[L]=0.298, F[0]=0.720, F[R]=-0.018.

Results are consistent with Standard Model predictions.

Set limits on anomalous tWb couplings gL and gR.

Abstract

A measurement of the W boson helicity is presented, where the W boson originates from the decay of a top quark produced in pp collisions. The event selection, optimized for reconstructing a single top quark in the final state, requires exactly one isolated lepton (muon or electron) and exactly two jets, one of which is likely to originate from the hadronization of a bottom quark. The analysis is performed using data recorded at a center-of-mass energy of 8 TeV with the CMS detector at the CERN LHC in 2012. The data sample corresponds to an integrated luminosity of 19.7 inverse femtobarns. The measured helicity fractions are F[L] = 0.298 +/- 0.028 (stat) +\- 0.032 (syst), F[0] = 0.720 +/- 0.039 (stat) +/- 0.037 (syst), and F[R] = -0.018 +/- 0.019 (stat) +/- 0.011 (syst). These results are used to set limits on the real part of the tWb anomalous couplings, gL and gR.