production via fragmentation at HERA

Abstract

We compute the contributions to large-p T J/ψ production at HERA coming from fragmentation of gluons and charm quarks. We find that the charm quark fragmentation contribution dominates over the direct production of J/ψ via photon-gluon fusion at large-p T , while the gluon fragmentation is negligibly small over the whole range of p T . An experimental study of p T distributions of J/ψ at HERA will provide a direct probe of the charm quark fragmentation functions.November 1995 * rohini@cts.iisc.ernet.in † dproy@theory.tifr.res.in ‡ sridhar@theory.tifr.res.in

Tevatron-hera colour-octet charmonium anomaly versus higher-order QCD effects

“…[24,25,26]. The analysis of resolved photoproduction [25,26] may be readily converted to hadroproduction by replacing the photon PDF's with the respective proton PDF's.…”

Color-singlet and color-octet contributions to photoproduction

“…At large transverse momenta, p ⊥ ∼ > 10 GeV, charm quark fragmentation dominates over the photon-gluon fusion process. 28,29 In contrast to what was found at the Tevatron 30 , gluon fragmentation into color-octet states is suppressed over the whole range of p ⊥ in the inelastic region z ∼ < 0.9. 29 A distinctive signal for color-octet processes should, however, be visible in the J/ψ energy distribution dσ/dz.…”

“…28,29 In contrast to what was found at the Tevatron 30 , gluon fragmentation into color-octet states is suppressed over the whole range of p ⊥ in the inelastic region z ∼ < 0.9. 29 A distinctive signal for color-octet processes should, however, be visible in the J/ψ energy distribution dσ/dz. 17 The linear combination of color-octet matrix elements that is probed by the J/ψ energy distribution does, however, depend on the value of z.…”

Validity of double scaling analysis in semi-inclusive processes – $J/\psi$ production at HERA

“…Fragmentation functions are computed perturbatively, at the initial scale of the order of the charm quark mass and the Altarelli-Parisi equations are then used to resum large logarithms in P T /m c . Gluon and charm fragmentation functions have been calculated [14], [15] and it has been shown [7] that at HERA experiments, the charm quark fragmentation process is expected to dominate over the quark gluon fusion process at sufficiently values of P T ≥ 7GeV . Having looked at J/Ψ production in the inelastic limit, we now move over to the diffractive region, i.e for values of the elasticity parameter z close to 1.…”