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Particles and Fields
Eur. Phys. J. C 27, 73-85 (2003)
DOI: 10.1140/epjc/s2002-01100-8

Unintegrated gluon in the photon and heavy quark production

L. Motyka1, 2 and N. Tîmneanu1

1  High Energy Physics, Uppsala University, Box 535, 751 21 Uppsala, Sweden
2  Institute of Physics, Jagellonian University, Reymonta 4, 30-059 Kraków, Poland

(Received: 4 September 2002 / Revised version: 6 November 2002 / Published online: 20 December 2002 )

The unintegrated gluon density in the photon is determined, using the Kimber-Martin-Ryskin prescription. In addition, a model of the unintegrated gluon is proposed, based on the saturation model extended to the large- x region. These gluon densities are applied to obtain cross sections for charm and bottom production in $\gamma^* p$ and $\gamma\gamma$ collisions using the kt factorization approach. We investigate both direct and resolved photon contributions and make a comparison with the results from the collinear approach and the experimental data. An enhancement of the cross section due to inclusion of non-zero transverse momenta of the gluons is found. The charm production cross section is consistent with the data. The data exceed our conservative estimate for bottom production in $\gamma p$ collisions, but theoretical uncertainties are too large to claim a significant inconsistency. A substantial discrepancy between theory and the experiment is found for $\gamma\gamma \to b\bar b X$, which is not cured by the kt factorization approach.

© Società Italiana di Fisica, Springer-Verlag 2003