Heavy-quark hadroproduction in k T -factorization approach with unintegrated gluon distributions
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ELEMENTARY PARTICLES AND FIELDS Theory
Heavy-Quark Hadroproduction in kT -Factorization Approach with Unintegrated Gluon Distributions* Yu. M. Shabelski** and A. G. Shuvaev*** Petersburg Nuclear Physics Institute, Russian Academy of Sciences, Gatchina, 188350 Russia Received April 26, 2005
Abstract—We consider the processes of heavy-quark production using the unintegrated gluon distributions. The numerical predictions for high-energy nucleon–nucleon and photon–nucleon collisions of the kT -factorization approach (semihard theory) are compared with the experimental data from the Tevatron collider and HERA. The total production cross sections and pT distributions are considered and they are in reasonable agreement with the data for reasonable values of QCD scale. PACS numbers : 25.75.Dw DOI: 10.1134/S1063778806020165
1. INTRODUCTION The investigation of heavy-quark production in high-energy hadron collisions is an important method for studying the quark–gluon structure of hadrons. The description of hard interactions in hadron collisions within the framework of QCD is possible only with the help of some phenomenology which reduces the hadron–hadron interaction to the parton– parton one via the formalism of the hadron structure functions. The cross sections of hard processes in hadron–hadron interactions can be written as the convolutions of squared matrix elements of the subprocess calculated within the framework of QCD, with the parton distributions in the colliding hadrons. The most popular and technically simplest approach is the so-called QCD collinear approximation, or parton model (PM). In this model, all particles involved are assumed to be on the mass shell, carrying only longitudinal momenta, and the cross section is averaged over two transverse polarizations of the incident gluons. The virtualities q 2 of the initial partons are taken into account only through their structure functions. The cross sections of the QCD subprocess are usually calculated in the next-to-leading order (NLO) of αs series [1–4]. The transverse momenta of the incident partons are neglected in the QCD matrix elements. This is the direct analogy of the ¨ Weizsacker–Williams approximation in QED. Another possibility to incorporate the incident parton transverse momenta is referred to as the ∗
The text was submitted by the authors in English. E-mail: [email protected] *** E-mail: [email protected] **
kT -factorization approach [5–10], or the theory of semihard interactions [11–19]. Here, the Feynman diagrams are calculated taking account of the virtualities and of all possible polarizations of the incident partons. In the small-x domain, there are no grounds to neglect the transverse momenta of the gluons, q1T and q2T , in comparison with the quark mass and transverse momenta piT . Moreover, at very high energies and very high piT , the main contribution to the cross sections comes from the region of q1T ∼ p1T or q2T ∼ p1T (see [20–22] for details). The QCD matrix elements of the subprocesses are rather complicated in suc
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