The sensitivity of R_pA to color recombination effects

TL;DR

This paper investigates how color recombination effects in hadronization models influence the spectra of particles produced in proton-nucleus collisions, showing that these effects can cause a multiplicity-dependent hardening of hadron spectra.

Contribution

It introduces a model implementation of color recombination effects in the SHERPA event generator and analyzes their impact on hadron spectra in proton-nucleus collisions.

Findings

Color recombination hardens the single inclusive hadron spectra.

The effect does not significantly depend on underlying event activity.

Jet spectra remain unaffected by color recombination effects.

Abstract

In hadronization models with color recombination, partons are allowed to regroup into color singlet structures that are different from those determined by the perturbative parton shower. This aims at modeling the possibility that soft interactions of partons with the underlying event can change color connections. If such an effect is at play in proton-proton collisions, it may be expected to be enhanced in proton-nucleus collisions due to the higher color charge density in the underlying event. Here, we provide a qualitative argument that color recombination effects could lead to a multiplicity dependent hardening of single inclusive hadron spectra that dies out very weakly with increasing transverse momentum. We present results of a (conservative) model implementation in the cluster hadronization model of the SHERPA event generator. In this model, we find that color recombination effects harden indeed the single inclusive hadron spectra without affecting the jet spectra, but that this effect does not depend significantly on underlying event activity. We explain this model feature and we argue why, in general, data on proton-nucleus collisions can help to constrain hadronization models used in proton-proton event generators.