Evidence for exclusive $γγ→W^{+}W^{−}$ production and constraints on anomalous quartic gauge couplings in pp collisions at $\sqrt{s}$=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 $\sqrt{s}$ = 8TeV, is reported using data corresponding to an integrated luminosity of 19.7fb$^{−1}$. Events are selected by requiring the presence of an electron-muon pair with large transverse momentum pT(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 $a_{0},c^{W}$ (dimension-6) and $f_{M0,1,2,3}$ (dimension-8), the most stringent to date, are derived from the measured dilepton transverse momentum spectrum.