Production of e+ e- in proton-lead collision: Photon-photon fusion

We analyze the photon-initiated processes for production of e(+)e(-) pairs in proton-nucleus collisions at LHC energy, taking into account both elastic processes and proton dissociations in the low-mass region (LMR) and intermediate-mass region (IMR) as defined by the ALICE collaboration. The calculations are performed within the k(T)-factorization approach, including transverse momenta of intermediate photons. We discuss several differential distributions in invariant mass of both the leptons M-ll, pair rapidity Y-ll and transverse momenta of the lepton pair p(t,ll). In addition, we present the two-dimensional distributions in log(10) x(Bj) and log(10) Q(2) and (log(10) W, log(10) Q(2)) the arguments of the deep-inelastic structure functions. All presented results were obtained with modern parametrizations of proton structure functions. Limiting to small invariant masses of dielectrons one tests structure functions in the nonperturbative region of small Q(2) and/or small W. We quantify difference for different parametrizations from the literature. We estimate gap survival factor and discuss experimental possibilities.

Automated summary

We analyze the process of producing e(+)e(-) pairs initiated by photons in proton-nucleus collisions at LHC energy, considering both elastic processes and proton dissociations. We discuss various distributions of different variables and find that testing the nonperturbative region of structure functions is possible with small invariant masses.