Semiexclusive dilepton production in proton-proton collisions with one forward proton measurement at the LHC

TL;DR

This paper analyzes semiexclusive dilepton production in proton-proton collisions at the LHC, considering photon-photon fusion mechanisms with one forward proton detection, including various processes, form factors, and survival factors.

Contribution

It provides a detailed theoretical and phenomenological analysis of semiexclusive dilepton production with forward proton detection, incorporating multiple mechanisms and comparing with simulation tools.

Findings

Weak dependence on dilepton invariant mass and transverse momentum.

Significant difference in gap survival factors between single-proton and inclusive cases.

Identifies the impact of different dissociation mechanisms on observables.

Abstract

We discuss photon-photon fusion mechanisms of dilepton production in proton-proton collisions with rapidity gap in the main detector and one forward proton in the forward proton detectors. This is relevant for the LHC measurements by ATLAS+AFP and CMS+PPS. Transverse momenta of the intermediate photons are taken into account and photon fluxes are expressed in terms of proton electromagnetic form factors and structure functions. Differential distributions in $\xi_{1/2}$, $M_{ll}$, $Y_{ll}$, $p_{t,ll}$, $M_R$ %pamietac wyjasnic M_R w tekscie are shown and the competition of different mechanisms is discussed. Both double-elastic and single-dissociative processes are included in the analysis. Different parametrizations of the structure functions are used. We discuss also mechanism with one forward $\Delta^+$ isobar, or other proton resonances in the final state. The role of several cuts is studied. We also use SuperChic generator and compare corresponding results to the results of our codes. The soft rapidity gap survival factor is calculated for each contribution separately. The gap survival factor for the single-dissociative mechanism due to minijet emission into the main detector is calculated in addition. It depends on the type of contribution (fully elastic, single dissociation, double dissociation). The soft rapidity gap survival factor for the case of single proton measurement is significantly smaller than that for the inclusive case (no proton measurement). We find only weak dependence on the invariant mass of the dilepton system as well as the lepton pair transverse momentum and sizeable dependence on the pair rapidity. The latter effect is rather difficult to identify experimentally.