Study of hard scattering processes in multihadron production from γγ collisions at LEP

The production of multihadronic states in ?? collisions at LEP has been studied with the DELPHI detector. The analyzed data correspond to an integrated luminosity of about 32pb-1, collected in the LEP runs of 1990–1992. Minimum bias data and a sample of events with jets at highpT have been selected under the requirement that no scattered electron or positron is observed. The two data sets have been compared to Monte Carlo predictions. The non-perturbative contribution described by the vector meson dominance Model and direct production from pointlike photons described by the quark parton model were found to be insufficient to reproduce the data. It has been necessary to include a third interaction component, which is due to perburbative hard scattering of the partonic constituents of the photon. Several parametrisations of the quark and gluon densities of the photon have been tested. The interplay with the cut in jet transverse momentum, which is necessary for the separation of the perturbative and non-perturbative regions, is discussed. The data favour parametrisations with rather soft partonic content of the photon.