Measurement of the polarization of W bosons with large transverse momenta in W+jets events at the LHC

Abstract

A first measurement of the polarization of W bosons with large transverse momenta in pp collisions is presented. The measurement is based on 36 pb⁻¹ of data recorded at √s=7 TeV by the CMS detector at the LHC. The left-handed, right-handed, and longitudinal polarization fractions (f_L, f_R, and f₀, respectively) of W bosons with transverse momenta larger than 50 GeV are determined by using decays to both electrons and muons. The muon final state yields the most precise measurement: (f_L-f_R)-=0.240±0.036(stat)±0.031(syst) and f₀^-=0.183±0.087(stat)±0.123(syst) for negatively charged W bosons and (f_L-f_R)+=0.310±0.036(stat)±0.017(syst) and f₀⁺=0.171±0.085(stat)±0.099(syst) for positively charged W bosons. This establishes, for the first time, that W bosons produced in pp collisions with large transverse momenta are predominantly left-handed, as expected in the standard model.