Study of Inclusive J/psi Production in Two-Photon Collisions at LEP II with the DELPHI Detector

TL;DR

This paper reports the observation of inclusive J/psi production in photon-photon collisions at LEP II, quantifying the cross-section and analyzing the photon structure contribution using PYTHIA simulations.

Contribution

First measurement of inclusive J/psi production in gamma-gamma collisions at LEP II, with analysis of the photon structure contribution to the process.

Findings

Observed 36 +/- 7 J/psi events with a cross-section of 45 +/- 9 (stat) +/- 17 (syst) pb.

Approximately 74% of J/psi events originate from resolved photon processes.

Gluon content of the photon is likely the dominant contribution to J/psi production.

Abstract

Inclusive J/psi production in photon-photon collisions has been observed at LEP II beam energies. A clear signal from the reaction gamma gamma -> J/psi+X is seen. The number of observed N(J/psi -> mu+mu-) events is 36 +/- 7 for an integrated luminosity of 617 pb^{-1}, yielding a cross-section of sigma(J/psi+X) = 45 +/- 9 (stat) +/- 17 (syst) pb. Based on a study of the event shapes of different types of gamma gamma processes in the PYTHIA program, we conclude that (74 +/- 22)% of the observed J/psi events are due to `resolved' photons, the dominant contribution of which is most probably due to the gluon content of the photon.