A study of the constraining power of high P_T observables in heavy-ion collisions

TL;DR

This paper investigates the effectiveness of high P_T observables in heavy-ion collisions to constrain theoretical models, revealing that some observables are insensitive to the underlying physics mechanisms, thus questioning their utility for model validation.

Contribution

It demonstrates that common high P_T observables may not effectively discriminate between different theoretical models of jet-medium interactions.

Findings

Jet yield observables are not very sensitive to the physics mechanism.

Some models known to be incorrect still agree with certain observables.

High P_T observables alone may not suffice to constrain models.

Abstract

Since the start of the LHC heavy ion program, a multitude of rather different high transverse momentum (P_T) observables has become available to study the physics of the interaction of hard partons with a QCD medium. Similarly, multiple theoretical models for this interaction exist and have been compared with available data, and regularly physics conclusions are drawn based on the agreement of a model with a particular data subset. However, such an agreement is only a necessary condition to identify a physics mechanism, not a sufficient one - it needs to be demonstrated that the agreement is not accidential or generic, in other words the observable actually needs to measure the physics in question. The aim of the study presented here is to illustrate this problem by computing various high P_T observables in three different models, two of which are known to be grossly wrong ab initio, and to study in which observables what amount of discrepancy with the data appears. The surprising outcome is that jet yield observables are not very sensitive to the physics mechanism of jet-medium interaction and hence do not constrain models well.