Transverse momentum resummation effects in W+W- measurements

The W+W- cross section has remained one of the most consistently discrepant channels compared to Standard Model (SM) predictions at the LHC, measured by both ATLAS and CMS at 7 and 8 TeV. Developing a better modeling of this channel is crucial to understanding properties of the Higgs and potential new physics. In this paper we investigate the effects of next-to-next-to-leading-log transverse momentum resummation in measuring the W+W- cross section. In the formalism we employ, transverse momentum resummation does not change the total inclusive cross section but gives a more accurate prediction for the pT distribution of the diboson system. By reweighting the pT distribution of events produced by Monte Carlo generators, we find a systematic shift that decreases the experimental discrepancy with the SM prediction by approximately 3%-7% depending on the Monte Carlo generator and parton shower used. The primary effect comes from the jet-veto cut used by both experiments. We comment on the connections to jet-veto resummation and other methods the experiments can use to test this effect. We also discuss the correlation of resummation effects in this channel with other diboson channels. Ultimately pT resummation improves the agreement between the SM and experimental measurements for most generators but does not account for the measured ∼20% difference with the SM, and further investigations into this channel are needed.