Constraining the physics of jet quenching

Abstract

Hard probes in the context of ultrarelativistic heavy ion collisions represent a key class of observables studied to gain informations about the QCD medium created in such collisions. However, in practice the so-called jet tomography has turned out to be more difficult than expected initially. One of the major obstacles in extracting reliable tomographic information from the data is that neither the parton-medium interaction nor the medium geometry are known with great precision, and thus a difference in model assumptions in the hard perturbative Quantum Choromdynamics (pQCD) modelling can usually be compensated by a corresponding change of assumptions in the soft bulk medium sector and vice versa. The only way to overcome this problem is to study the full systematics of combinations of parton-medium interaction and bulk medium evolution models. This work presents a meta-analysis summarizing results from a number of such systematical studies and discusses in detail how certain data sets provide specific constraints for models. Combining all available information, only a small group of models exhibiting certain characteristic features consistent with a pQCD picture of parton-medium interaction is found to be viable given the data. In this picture, the dominant mechanism is medium-induced radiation combined with a surprisingly small component of elastic energy transfer into the medium.

Towards the understanding of jet shapes and cross sections in heavy ion collisions using soft-collinear effective theory

“…They share the common physical picture of the parton energy loss, but with emphasis on physics at different energy scales. It has been clear that hadron cross section suppression alone is not enough to identify and distinguish between different physical mechanisms in jet quenching [46][47][48], and more differential and correlated measurements are needed [49,50].…”

Suppression and energy loss in Quark-Gluon Plasma

“…The predictions of the model were then comprehensively tested against angular averaged R AA data, which is considered to be largely insensitive to the medium evolution [44,45]. We obtained robust agreement for wide range of probes, centralities and beam energies.…”

Medium Modification ofγJets in High-Energy Heavy-Ion Collisions

“…In addition, one also expects to see a modification of the jet fragmentation function and jet transverse profile. A large dijet asymmetry in central Pb+Pb collisions at √ s = 2.76 TeV is indeed observed at the Large Hadron Collider (LHC) [5], consistent with the picture of jet quenching [6][7][8][9][10]. However, two puzzles in jet modification still lack satisfactory explanations.…”