Distorting the Hump-backed Plateau of Jets with Dense QCD Matter

TL;DR

This paper develops a new formulation for medium-induced parton energy loss in QCD, analyzing how dense medium modifies jet fragmentation patterns, especially the hump-backed plateau, in heavy ion collisions.

Contribution

It introduces a comprehensive model treating all parton branchings equally and links medium effects to observable modifications in jet fragmentation distributions.

Findings

Strong suppression of hadron spectra in Au-Au collisions at RHIC.

Distortion of the hump-backed plateau due to medium effects.

Soft jet fragments can be measured above certain momentum cuts.

Abstract

The hump-backed plateau of the single inclusive distribution of hadrons inside a jet provides a standard test of the interplay between probabilistic parton splitting and quantum coherence in QCD. The medium-induced modification of this QCD radiation physics is expected to give access to the properties of the dense medium produced in relativistic heavy ion collisions. Here, we introduce a formulation of medium-induced parton energy loss, which treats all leading and subleading parton branchings equally, and which - for showering in the vacuum - accounts for the observed distribution of soft jet fragments. We show that the strong suppression of single inclusive hadron spectra measured in Au-Au collisions at the Relativistic Heavy Ion Collider (RHIC) implies a characteristic distortion of the hump-backed plateau; we determine, as a function of jet energy, to what extent the soft jet fragments can be measured above some momentum cut. Our study further indicates that the approximate pT-independence of the measured nuclear modification factor does not exclude a significant Q^2-dependence of parton energy loss.