QCD diffractive mechanism of exclusive $W^+W^-$ pair production at high energies

Abstract

We discuss new diffractive mechanism of central exclusive production of $W^+W^-$ pairs in proton-proton collisions at the LHC. We include diagrams with intermediate virtual Higgs boson as well as quark box diagrams. Several observables related to this process are calculated. Predictions for the total cross section and differential distributions in $W$-boson rapidity and transverse momentum as well as $WW$ invariant mass are presented. We also show results for different polarization states of the final $W^{\pm}$ bosons. We compare the contribution of the $\gamma \gamma \to W^+ W^-$ mechanism considered in the literature with the contribution of the diffractive mechanism through the $gg \to W^+ W^-$ subprocess for the different observables. The phase space integrated diffractive contribution when separated is only a small fraction of fb compared to 115.4 fb of the $\gamma\gamma$-contribution without absorption. The latter contribution dominates at small four-momentum transfers squared in the proton lines and in a broad range of $W^+ W^-$ invariant masses. This offers a possibility of efficient searches for anomalous triple-boson ($\gamma W W$) and quartic-boson ($\gamma \gamma WW$) couplings and testing models beyond the Standard Model. We discuss shortly also the $p p \to p p \gamma \gamma$ process, where the box contribution is very similar to that for $W^+ W^-$ and compare our results with recent CDF data. Nice agreement has been achieved without additional free parameters.