How many interactions does it take to modify a jet?

TL;DR

This paper investigates how many interactions are necessary to modify jets in small collision systems, using a simple model to explain the relationship between jet quenching observables and the number of scatterings.

Contribution

It introduces a scaling relation between jet quenching observables and the number of scatterings, providing insights into jet modifications in small systems.

Findings

A large number of scatterings are needed for measurable jet quenching.

The observed $v_2$ can be consistent with $R_{AA}$ within experimental uncertainties.

Scaling relations hold approximately for small modifications, with deviations due to inelastic energy loss.

Abstract

It is a continued open question how there can be an azimuthal anisotropy of high $p_\perp$ particles quantified by a sizable $v_2$ in p+Pb collisions when, at the same time, the nuclear modification factor $R_\text{AA}$ is consistent with unity. We address this puzzle within the framework of the jet quenching model \textsc{Jewel}. In the absence of reliable medium models for small collision systems we use the number of scatterings per parton times the squared Debye mass to characterise the strength of medium modifications. Working with a simple brick medium model we show that, for small systems and not too strong modifications, $R_\text{AA}$ and $v_2$ approximately scale with this quantity. We find that a comparatively large number of scatterings is needed to generate measurable jet quenching. Our results indicate that the $R_\text{AA}$ corresponding to the observed $v_2$ could fall within the experimental uncertainty. Thus, while there is currently no contradiction with the measurements, our results indicate that $v_2$ and $R_\text{AA}$ go hand-in-hand. We also discuss departures from scaling, in particular, due to sizable inelastic energy loss.