Charge asymmetry phenomenon for the leptonically decaying W γ pair at NNLO QCD

The paper presents for the first time a phenomenological assessment which focuses on the charge asymmetry phenomenon for the W γ production process with subsequent leptonic decay modes W+γ → l+νlγ and W−γ → l−νl¯γ in proton-proton (pp) collisions. Charge asymmetry for the leptonic W γ process is predicted by the inclusion of genuine next-to-next-to-leading order (NNLO) corrections in the QCD perturbation theory. NNLO predictions of asymmetry distributions are assessed for the key observables, including the decay lepton and photon pseudorapidities ηl and ηγ, respectively, and the lepton-photon pseudorapidity correlation Δη(l, γ). The predictions are presented by focusing on realistic fiducial phase-space definitions in comparison at various pp-collision energies of 13 TeV, 14 TeV, and 100 TeV. The sensitivity of the predicted asymmetry distributions to an important observation known as radiation amplitude zero in the W γ process is reported. The asymmetry distribution for the Δη(l, γ) is shown to be important for probing the radiation-zero effect in the presence of high-transverse momentum photons. The impact of imposing jet veto for the final state of the W γ process on the asymmetry distributions is reported for future pp-collision energies. Prospects of phase-space definitions including a jet veto and harder-photon recoil are discussed to compensate for the negative impact of increasing collision energy on the asymmetry distributions. The charge asymmetry distributions are proposed as sensitive observables that offer a unique opportunity for stringent tests of the SM and represent a novel method for probing departure from the SM in indirect searches for new-physics effects, independently from the existing direct searches for anomalous WW γ coupling regarding the W γ final state.