Breakdown of kT-factorization and J/Psi production in dA collisions

TL;DR

This paper examines the validity of kT-factorization in different particle productions during high-energy collisions, revealing its limitations for J/psi production and confirming its applicability for open charm at RHIC.

Contribution

It demonstrates the breakdown of kT-factorization for J/psi production and confirms its approximate validity for open charm in dA collisions, providing insights into cold nuclear matter effects.

Findings

kT-factorization holds for open charm with 10-20% accuracy at RHIC.

Breakdown of factorization is severe for J/psi production.

Calculated J/psi multiplicity agrees with experimental data.

Abstract

In spite of the sweeping coherence effects in high energy hadron and nuclei collisions, $k_T$-factorization can be recovered for the inclusive gluon production in $pA$ collisions at the leading logarithmic order. In open charm production at RHIC $k_T$-factorization holds numerically with about 10-20% accuracy. This allows to extrapolate the cold nuclear matter effect observed in light and charm meson production in $dA$ collisions to that in $AA$ ones. Unlike the open charm, the breakdown of factorization in $J/\psi$ production is severe. Indeed, already at the lowest order in gluon density the main contribution to the inclusive cross section is proportional to the square of gluon density in the nucleus. As a consequence, one cannot infer the cold nuclear matter effect on $J/\psi$ production in $AA$ collisions from that in $dA$. We present the calculation of $J/\psi$ multiplicity in the framework of the CGC (color glass condensate)/saturation and show that it agrees with the experimental data.