Evidence for exclusive γγ → W + W − production and constraints on anomalous quartic gauge couplings in pp collisions at √s=7 and 8 TeV

Abstract

A search for exclusive or quasi-exclusive γγ → W + W − production, via pp → p (*) W + W − p (*) → p (*) μ ±e∓ p (*) at s√=8 TeV, is reported using data corresponding to an integrated luminosity of 19.7 fb−1. Events are selected by requiring the presence of an electron-muon pair with large transverse momentum p T(μ ±e∓) > 30 GeV, and no associated charged particles detected from the same vertex. The 8 TeV results are combined with the previous 7 TeV results (obtained for 5.05 fb−1 of data). In the signal region, 13 (2) events are observed over an expected background of 3.9 ± 0.6 (0.84 ± 0.15) events for 8 (7) TeV, resulting in a combined excess of 3.4σ over the background-only hypothesis. The observed yields and kinematic distributions are compatible with the standard model prediction for exclusive and quasi-exclusive γγ → W + W − production. Upper limits on the anomalous quartic gauge coupling operators a W0,C (dimension-6) and f M0,1,2,3 (dimension-8), the most stringent to date, are derived from the measured dilepton transverse momentum spectrum.