Heavy-quark correlations in direct photon-photon collisions

Abstract

In two-photon collisions at LEP2 and a future e + e − linear collider heavy quarks (mainly charm) will be pair-produced rather copiously. The production via direct and resolved photons can be distinguished experimentally via a remnant-jet tag. We study correlations of the heavy quarks at next-to-leading order in QCD in the direct channel, which is free from phenomenological parton densities in the photon. These correlations are therefore directly calculable in perturbative QCD and provide a stringent test of the production mechanism.

production in two-photon collisions

“…We want to emphasize that our programs are different from the usual Monte-Carlo partonshower codes, since they result from fixed-order QCD computations, where no collinear approximation (and no shower evolution) has been performed. For the direct channel, the NLO program has been constructed in [6], while for the single-resolved and double-resolved channels we use the NLO programs constructed in refs. [4,5].…”

“…We use fully differential NLO Monte Carlo programs for all the production mechanisms, constructed in refs. [4][5][6]. Earlier studies either focused on an individual component of the production [6], or had mostly HERA data in mind [4,5], or did not include fragmentation functions [7].…”

“…[4][5][6]. Earlier studies either focused on an individual component of the production [6], or had mostly HERA data in mind [4,5], or did not include fragmentation functions [7]. Moreover, a relatively large number of NLO-evolved photonic parton distributions [8][9][10][11], and new studies on charm fragmentation functions [12][13][14] are available, some of them incorporating the most recent theoretical and experimental findings.…”

Charm quark andD*±cross sections in deeply inelastic scattering at DESY HERA

“…Herein, the calculation itself is discussed and the variation with respect to the theoretical parameters is studied. Heavy quark correlations have also been calculated for hadroproduction [13], photoproduction [14], and photon-photon collisions [15,16] allowing for the possiblility of an extensive comparison with experimental data.…”

Double-photon exclusive processes with heavy-quark–heavy-antiquark pairs in high-energy Pb-Pb collisions at energies available at the CERN Large Hadron Collider

“…Here we include leading-order corrections only for the dominant, in heavy-ion collisions, direct contribution. The details concerning the higher-order corrections to heavy quark and heavy antiquark production in photon-photon collisions can be found in [10][11][12][13][14][15][16][17]. In α s -order there are one-gluon bremsstrahlung diagrams (γγ → Q Qg) and interferences of the Born diagram with self-energy diagrams (in γγ → Q Q) and vertexcorrection diagrams (in γγ → Q Q).…”