Energy Loss in Small Collision Systems

TL;DR

This paper investigates energy loss mechanisms in small collision systems like p+Pb and Pb+Pb, highlighting the impact of short pathlength corrections on particle suppression and challenging conventional elastic energy loss models.

Contribution

It introduces a short pathlength correction to radiative energy loss models, significantly affecting suppression predictions in small collision systems.

Findings

Short pathlength correction has minimal effect on D mesons.

Large reduction in pion suppression due to short pathlength correction.

Conventional elastic models overpredict suppression in p+A collisions.

Abstract

We present leading hadron suppression predictions in $Pb+Pb$ and $p+Pb$ collisions from a convolved radiative and collisional energy loss model in which partons propagate through a realistic background, and in which the radiative energy loss receives a short pathlength correction. We find that the short pathlength correction is small for $D$ meson $R_{AA}(p_T)$ in both $Pb+Pb$ and $p+Pb$ collisions. However the short pathlength correction leads to a surprisingly large reduction in suppression for $\pi$ mesons in $p+Pb$ and even $Pb+Pb$ collisions, providing a qualitative explanation for the rapid rise in $\pi$ meson $R_{AA}(p_T)$ at the LHC. We find that the size of the short pathlength correction to $R_{AA}(p_T)$ is acutely sensitive to the chosen distribution of scattering centers in the plasma. Furthermore we find that conventional elastic energy loss models, which apply the central limit theorem to the number of scatterings, dramatically overpredict suppression in $\mathrm{p}+\mathrm{A}$ collisions, calling for short pathlength corrections to elastic energy loss.