# Absence of jet quenching in peripheral nucleus-nucleus collisions

## TL;DR

This paper shows that apparent suppression of high-$p_T$ particles in peripheral nucleus-nucleus collisions can be caused by geometric biases, not jet quenching, affecting interpretations of energy loss and medium effects.

## Contribution

The study demonstrates that event selection and geometry biases significantly influence $R_{AA}$ in peripheral collisions, challenging previous assumptions about jet quenching absence.

## Key findings

- Peripheral $R_{AA}$ can be suppressed without jet quenching due to biases.
- Biases affect all hard probes and collision energies.
- Results suggest revising jet quenching estimates in peripheral collisions.

## Abstract

Medium effects on the production of high-$p_{\rm T}$ particles in nucleus-nucleus (AA) collisions are generally quantified by the nuclear modification factor ($R_{\rm AA}$), defined to be unity in absence of nuclear effects. Modeling particle production including a nucleon-nucleon impact parameter dependence, we demonstrate that $R_{\rm AA}$ at midrapidity in peripheral AA collisions can be significantly affected by event selection and geometry biases. Even without jet quenching and shadowing, these biases cause an apparent suppression for $R_{\rm AA}$ in peripheral collisions, and are relevant for all types of hard probes and all collision energies. Our studies indicate that calculations of jet quenching in peripheral AA collisions should account for the biases, or else they will overestimate the relevance of parton energy loss. Similarly, expectations of parton energy loss in light-heavy collision systems based on comparison with apparent suppression seen in peripheral $R_{\rm AA}$ should be revised. Our interpretation of the peripheral $R_{\rm AA}$ data would unify observations for lighter collision systems or lower energies where significant values of elliptic flow are observed despite the absence of strong jet quenching.