The photon structure from deep inelastic electron–photon scattering

Abstract

The present knowledge of the structure of the photon is presented with emphasis on measurements of the photon structure obtained from deep inelastic electron-photon scattering at e + e − colliders. This review covers the leptonic and hadronic structure of quasi-real and also of highly virtual photons, based on measurements of structure functions and differential cross-sections. Future prospects of the investigation of the photon structure in view of the ongoing LEP2 programme and of a possible linear collider are addressed. The most relevant results in the context of measurements of the photon structure from photon-photon scattering at LEP and from photonproton and electron-proton scattering at HERA are summarised.

Hadronic structure of the photon at smallxin holographic QCD

“…As to the four-momentum squared of the target photon, we focus on the real photon case, but P 2 cannot be exactly zero in practice. Events with P 2 ∼ O(0.01) GeV 2 have been measured [11,12], so we assume a quasi-real photon with P 2 = 0.01 GeV 2 as the target particle here [8].…”

Measurement of the charm structure function F2,c of the photon at LEP

“…Thus, only the combinatorial background from deep-inelastic electron-photon scattering events e + e − → e + e − qq with q = u, d, s and c has to be subtracted from the data. The production of bottom quarks is suppressed compared to charm production due to the larger mass and smaller charge and is negligible [1]. Figure 2 shows the difference between the D ⋆ and D 0 candidate masses for both decay channels combined.…”

“…Much of the present knowledge of the structure of the photon has been obtained from deepinelastic electron-photon 1 scattering at e + e − colliders [1]. With the high statistics available at LEP2, it is possible to investigate the flavour composition of the hadronic structure function F γ 2 .…”

Structure functions for the virtual and real photons

“…Ten years later the first data on the production of large p T particles and jets in the photon-induced processes, so called resolved photon processes, have appeared for both real and virtual photons. Review of data can be found in [14], [15].…”

“…Here (quasi) real photons with a Weizsäcker-Williams energy spectrum play a role of a target. The F γ 2 | l data for l = µ together with QED predictions are summarized in Fig.2, from [14].…”