Energy dependence of the dijet imbalance in Pb-Pb collisions at 2.76 ATeV

TL;DR

This paper investigates how the energy dependence of dijet imbalance in Pb-Pb collisions at 2.76 TeV relates to jet quenching, using the YaJEM in-medium shower code to compare with CMS data and analyze jet collimation effects.

Contribution

It introduces a comparison of the YaJEM in-medium shower model with CMS data to understand the energy dependence of dijet imbalance and jet collimation effects.

Findings

Dijet imbalance decreases with jet P_T due to kinematical collimation.

No evidence for non-trivial energy dependence of shower-medium interactions.

Models attributing collimation solely to medium modification are ruled out.

Abstract

The appearance of monojets is among the most striking signature of jet quenching in the context of ultrarelativistic heavy-ion collisions at the Large Hadron Collider. Experimentally, the asymmetry of back-to-back jets is quantified in terms of the dijet imbalance distribution by the ATLAS and CMS collaborations. Recently, the CMS collaboration has also studied the trigger jet momentum (P_T) dependence of the imbalance in the range between 120 and 500 GeV which is found to decrease with jet P_T. In this work, results from the in-medium shower code YaJEM are compared with this data set. These results suggest that the main effects observed in the data are the kinematical collimation of jets and the increase in the probability to produce more collimated quark jets with jet P_T, whereas there is no indication for any non-trivial energy dependence of the shower-medium interaction mechanism itself. The data furthermore can rule out models in which the jet shape is collimated due to the medium modification.