P. Abreu et al., FIRST EVIDENCE OF HARD SCATTERING PROCESSES IN SINGLE TAGGED GAMMA-GAMMA-COLLISIONS, Physics letters. Section B, 342(1-4), 1995, pp. 402-416
For the first time, multihadronic production from single tagged gamma
gamma collisions has been studied, where one of the scattered leptons
was tagged at very low virtual photon absolute mass squared ([Q(2)] =
0.06 (GeV/c(2))(2)). Data collected during 1991 and 1992 in the DELPHI
experiment at LEP are shown to agree well with predictions which incl
uded the non-perturbative vector meson dominance model in which the in
teracting photons are assumed to have converted into a vector meson (r
ho, omega or pi), a quark-parton model which describes direct photon i
nteractions and a QCD-based model which considers the photon to have q
uark and gluon structure functions. Five different parametrizations of
these structure functions were used and the predictions compared with
the data. This study confirms recent results from no-tag experiments
in requiring a QCD-based component to successfully describe the data,
indicating that the photon has a significant partonic content.