title: Evidence for the color-octet mechanism from CERN LEP2 gamma gamma --> J/psi + X Data.
abstract: We present theoretical predictions for the transverse-momentum distribution of J/psi mesons promptly produced in gammagamma collisions within the factorization formalism of nonrelativistic quantum chromodynamics, including the contributions from both direct and resolved photons, and we perform a conservative error analysis. The fraction of J/psi mesons from decays of bottom-flavored hadrons is estimated to be negligibly small. New data taken by the DELPHI Collaboration at LEP2 nicely confirm these predictions, while they disfavor those obtained within the traditional color-singlet model.
authors.affiliation: II. Institut für Theoretische Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Klasen
authors.forename: Bernd A
authors.initials: BA
authors.lastname: Kniehl
authors.forename: Luminiţa N
authors.initials: LN
authors.lastname: Mihaila
authors.forename: Matthias
authors.initials: M
authors.lastname: Steinhauser