Inelastic photoproduction

Abstract

Inelastic photoproduction of J/ψ particles at high energies is one of the processes to determine the gluon distribution in the nucleon. We have calculated the QCD radiative corrections to the color-singlet model of this reaction. They are large at moderate photon energies, but decrease with increasing energies. The cross section and the J/ψ energy spectrum are compared with the available fixed-target photoproduction data and predictions are given for the HERA energy range. * Supported in part by Deutsche Forschungsgemeinschaft DFG † Present address: Deutsches Elektronen-Synchrotron DESY,

Color singlet relativistic correction inJ/ψphotoproduction

“…The constraints: z ≤ 0.8 and p t ≥ 1 GeV, valid at HERA, are adopted. The K factor, consistent with these cuts, from the NLO corrections to the color singlet channel [10] is K ≈ 1.8. Figure 2 shows the total cross section as a function of the photon-nucleon center of mass energy, √ s. The leading order color singlet contribution (long dashed line), accounts quite well for most of the data from HI [3] (circles) and ZEUS [4] (squares).…”

“…However, it has been noted earlier that the rates are sensitive to α s (m), m, and the choice of parton distribution functions, which are not precisely known. Certainly it seems that the uncertainty in these parameters, correspond to variations in the rates which are of similar magnitude, or greater than the effect of the O(v 2 ) correction [10]. Therefore, at the present level of precision, it is not possible to observe the effect of the correction in experiments.…”

“…The O(v 2 ) contribution has not been computed within NRQCD. It has been pointed out by Bodwin et al [6], that corrections of O(v 2 ) may be as important as radiative corrections of O(α s ), which have already been calculated for photoproduction [10], and found to be significant. Without a detailed understanding of the O(v 2 ) term, it is not possible to make an assessment of the significance of the color octet terms: the O(v 2 ) contribution is clearly necessary for consistency, according to the power counting rules of NRQCD.…”

Inelastic electroproduction of ηc at ep colliders

“…We note that the next to leading order QCD perturbative corrections are large for J/ψ photoproduction at HERA energy ranges [8,17,18]. These corrections change the normalization of the production rate by a factor of about 2. η c photoproduction and electroproduction may also be affected by these corrections.…”

Color-singlet and color-octet contributions to photoproduction

“…14 The calculation of the higher-order perturbative QCD corrections to the short-distance cross section (2) has been performed recently. 15,16 Generic diagrams which build up the cross section in next-to-leading order (NLO) are depicted in Fig.1. Besides the usual self-energy diagrams and vertex corrections for photons and gluons (b), one encounters box diagrams (c), the splitting of the final-state gluon into gluon and light quark-antiquark pairs, as well as diagrams renormalizing the initial state parton densities (e).…”