NNLO QCD predictions of the asymmetry probe of the Z? pair-production process

The paper presents for the first time a novel idea of exploiting asymmetry between differential cross sections of the off-shell Z gamma pair-production in proton-proton (pp) collisions for the final states of a charged-lepton pair plus a photon pp -> Z gamma -> l(+)l(-)gamma (leptonic decay) and of a neutrino pair plus a photon (invisible decay). Asymmetry between the leptonic and invisible decays of the Z gamma process is investigated by using fixed-order predictions through inclusion of next-to-next-to-leading (NNLO) radiative corrections in quantum chromodynamics (QCD) perturbation theory. NNLO QCD predictions are presented at various pp-collision energies as functions of several key observables including transverse momenta and azimuthal-angle separation, regarding the Z gamma decay products. The predicted distributions for the Z gamma asymmetry are provided based on realistic fiducial phase-space requirements in line with the related hadron-collider measurements. The predicted distributions are assessed at various pp-collision energies and in different phase-space regions such as with higher lepton-pair invariant mass m(l+l- )higher neutrino-pair transverse momentum p(T)(vv-)requirements. The Z gamma asymmetry is shown to be significantly sensitive in different regions of phase space including high- m(l+l-) and high-p(T)(vv-)regions. The Z gamma asymmetry can therefore be translated into an important quantity for probing deviation from the Standard Model(SM)predictions. In this regard, the asymmetry probe is proposed as a sensitive indicator for indirect searches for physics beyond the SM encompassing high-mass resonances and dark-matter sector