J/psi 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.

Figures (2)

• Figure 1: $d\sigma/dp_T$ (in nb/GeV) for inclusive $J/\psi$ production at HERA for photon energy $\nu=40$ GeV (upper figure) and $\nu=100$ GeV (lower figure). The solid line represents the fusion contribution and the dashed-dotted line the charm quark fragmentation contribution. The dotted and dashed lines represent the gluon fragmentation contributions with and without a colour-octet component for the $S$-state. The cut on the inelasticity parameter, $z$, is $0.1 < z <0.9$.
• Figure 2: $d\sigma/dp_T$ (in nb/GeV) for photon energy $\nu=100$ GeV. The solid line represents the fusion contribution, and the dashed line the charm quark fragmentation contribution, using a cut $z < 0.5$.