Evidence for exclusive gg W+W production and constraints on anomalous quartic gauge couplings in pp collisions at s=7$ \sqrt{s}=7 and 8 TeV
A bstractA search for exclusive or quasi exclusive gg W+W production, via pp p()W+W p( p()m+ ep( at s=8$ \sqrt{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 pT(m+ 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 3.4s over the background only hypothesis. The observed yields and kinematic distributions are compatible with the standard model prediction for exclusive and quasi exclusive gg W+W production. Upper limits on the anomalous quartic gauge coupling operators a0,CW (dimension 6) and fM0,1,2,3 (dimension 8) the most stringent to date, are derived from the measured dilepton transverse momentum spectrum.