Charmonium production at the Tevatron and Large Hadron Collider in the Regge limit of QCD
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EMENTARY PARTICLES AND FIELDS Theory
Charmonium Production at the Tevatron and Large Hadron Collider in the Regge Limit of QCD M. A. Nefedov* , V. A. Saleev** , and A. V. Shipilova*** Samara State University, ul. Akademika Pavlova 1, Samara, 443011 Russia Received April 3, 2012
Abstract—Processes involving direct J/ψ-meson production in proton–antiproton and proton–proton collisions are studied under the assumption of gluon Reggeization in t-channel exchanges and with the aid of the formalism of nonrelativistic quantum chromodynamics. The present calculations are performed in the leading approximation in the strong coupling constant αs and in the relative quark velocity v. The octet nonperturbative matrix elements for the transition of a c¯ c pair to quarkonium are fixed in fitting the transverse-momentum spectra obtained by the CDF Collaboration for J/ψ mesons at the Tevatron collider. The spectra of J/ψ-meson production at the energies of the Large Hadron Collider are predicted, and the resulting predictions agree well with experimental data obtained by the ATLAS, CMS, and LHCb √ Collaborations at S = 7 TeV. DOI: 10.1134/S1063778813110124
1. INTRODUCTION The production of heavy quarkonia at hadron colliders provides a powerful tool for testing the highenergy limit of quantum chromodynamics (QCD) and for studying the relative role of perturbative and nonperturbative effects in such processes. √ The total collision energies of S = 1.8 and 1.96 TeV at the√Tevatron, to say nothing of their counterparts of S = 7 and 14 TeV at the Large Hadron Collider (LHC), exceed substantially the characteristic hard-process energy scale μ, which is about the quarkonium transverse mass MT =
M 2 + p2T ; that is, the following scale-parameter hi√ erarchy holds: ΛQCD μ S. In this high-energy limit, known as the Regge limit, the contributions of parton subprocesses involving the exchange of a t-channel gluon or quark become dominant. In view of this, it is no longer legitimate to disregard the transverse momentum of Reggeized t-channel partons and their virtuality in the initial state. Processes involving t-channel exchange obey so-called multi-Regge kinematics, in which case final-state particles are widely separated in rapidity. The case where groups of particles are separated in rapidity is referred to as the case of multi-Regge kinematics. *
E-mail: [email protected] E-mail: [email protected] *** E-mail: [email protected] **
For the case of J/ψ-meson production, this kinematics looks as follows: a J/ψ meson in the case of multi-Regge kinematics or a J/ψ meson together with a gluon jet in the case of quasi-multi-Regge kinematics is produced in the central rapidity region, the remaining particles being produced with rapidities that are high in absolute value. The parton-Reggeization approach [1, 2] is highly efficient in the phenomenology of high-energy physics, and this demonstrates a dominant role of the multiRegge- and quasi-multi-Regge-kinematics production mechanisms in hard processes. This approach was success
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