Fragmentation production of J/psi and psi' at the Tevatron

TL;DR

This paper investigates J/psi and psi' production at the Tevatron at large pT using a fragmentation framework. It computes gluon and charm fragmentation into charmonium, including feeddown from chi_c states, and evolves fragmentation functions with Altarelli-Parisi equations, supplemented by NLO corrections for charm production. The main result is that fragmentation, especially g to chi_c followed by chi_c to psi gamma, dominates prompt J/psi production at high pT and is broadly compatible with CDF and D0 data given theoretical uncertainties, while leading-order direct production severely underestimates the rate. For psi', fragmentation produces the correct pT dependence but underpredicts the experimental rate by more than an order of magnitude, suggesting missing mechanisms such as higher-order processes; the paper discusses potential extensions and ongoing work to refine the framework.

Abstract

We present a calculation of the charm and gluon fragmentation contributions to inclusive $J/ψ$ and $ψ'$ production at large transverse momentum at the Tevatron. For $ψ$ production, we include both fragmentation directly into $ψ$ and fragmentation into $χ_c$ followed by the radiative decay $χ_c \to ψ+ γ$. We find that fragmentation overwhelms the leading-order mechanisms for prompt $ψ$ production at large $p_T$, and that the dominant contributions come from fragmentation into $χ_c$. Our results are consistent with recent data on $ψ$ production from the CDF and D0 experiments. In the case of prompt $ψ'$ production, the dominant mechanism at large $p_T$ is charm fragmentation into $ψ'$. We find serious disagreement between our theoretical predictions and recent $ψ'$ data from the Tevatron.