Resolved photon processes

Abstract

We review high-energy scattering processes that are sensitive to the hadronic structure of the photon, describing theoretical predictions as well as recent experimental results. These processes include deep-inelastic electron-photon scattering at e + e − colliders; and the production of jets, heavy quarks and isolated photons in the collision of real photons at e + e − colliders, as well as in photon-proton collisions at ep colliders. We also comment on "minijet" based calculations of total γp and γγ cross-sections, and discuss the possibility that future linear e + e − colliders might produce very large photon fluxes due to the "beamstrahlung" phenomenon; in the most extreme cases, we predict more than one hadronic γγ event to occur at every bunch crossing.

Gluon Sivers function and transverse single spin asymmetries in $e + p^\uparrow \rightarrow γ+ X$

“…In the present work, we have considered TSSAs in the low-virtuality electroproduction of prompt photons at EIC energy using both GPM and CGI-GPM approaches. We have taken into account along with the direct photon contribution, also the resolved photon contribution to prompt photon production where the partonic scattering takes place between a parton originating from the quasi-virtual photon emitted by the incoming electron and the parton from the polarized proton [30][31][32]. Further in CGI-GPM computation, the major contribution comes from f-type GSF while contribution of QSF and d-type GSF to asymmetry are nearly zero.…”

Soft gluons and the energy dependence of total cross-sections

“…The first question about treating together the pp, p p case on the one hand and the γp, γγ case on the other, arises naturally as the 'hadronic' structure [1] of the photon has now been established in both e + e − and ep experiments conclusively [2]. Further, the photonic partons seem to have nontrivial effects on the photon-induced processes at high energies [3].…”

QCD and total cross-sections : photons and hadrons

“…This model ascribes the rise of the total cross-sections to the increasing number of low p T partons, and their collisions. The present knowledge of parton densities in the hadrons has now been extended to photons by the studies of the resolved photon processes, at HERA and LEP 2,3 . Recently measurements of total cross-sections for photonic processes have become available from HERA 4,5 and LEP 6,7,8,9 .…”