Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at root s=8 TeV

Abstract

<jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb<jats:sup><jats:italic>−</jats:italic>1</jats:sup> for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (<jats:italic>F</jats:italic><jats:sub>0</jats:sub>), left-handed (<jats:italic>F</jats:italic><jats:sub>L</jats:sub>), or right-handed (<jats:italic>F</jats:italic><jats:sub>R</jats:sub>) polarizations. The resulting combined measurements of the polarization fractions are <jats:italic>F</jats:italic><jats:sub>0</jats:sub> = 0<jats:italic>.</jats:italic>693 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>014 and <jats:italic>F</jats:italic><jats:sub>L</jats:sub> = 0<jats:italic>.</jats:italic>315 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>011. The fraction <jats:italic>F</jats:italic><jats:sub>R</jats:sub> is calculated from the unitarity constraint to be <jats:italic>F</jats:italic><jats:sub>R</jats:sub> = <jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>008 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for <jats:italic>F</jats:italic><jats:sub>0</jats:sub> (<jats:italic>F</jats:italic><jats:sub>L</jats:sub>) with respect to the most precise single measurement. A limit on anomalous right-handed vector (<jats:italic>V</jats:italic><jats:sub>R</jats:sub>), and left- and right-handed tensor (<jats:italic>g</jats:italic><jats:sub>L</jats:sub><jats:italic>, g</jats:italic><jats:sub>R</jats:sub>) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [<jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>11<jats:italic>,</jats:italic> 0<jats:italic>.</jats:italic>16] for <jats:italic>V</jats:italic><jats:sub>R</jats:sub>, [<jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>08<jats:italic>,</jats:italic> 0<jats:italic>.</jats:italic>05] for <jats:italic>g</jats:italic><jats:sub>L</jats:sub>, and [<jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>04<jats:italic>,</jats:italic> 0<jats:italic>.</jats:italic>02] for <jats:italic>g</jats:italic><jats:sub>R</jats:sub>, at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.</jats:p>