Measurement of the Polarization of W Bosons with Large Transverse Momenta in W+jets Events at the LHC

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[superscript -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[subscript L], f[subscript R], and f[subscript 0], 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[subscript L]-f[subscript R])-=0.240±0.036(stat)±0.031(syst) and f[subscript 0][superscript -]=0.183±0.087(stat)±0.123(syst) for negatively charged W bosons and (f[subscript L]-f[subscript R])[superscript +]=0.310±0.036(stat)±0.017(syst) and f[subscript 0][superscript +]=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.