Systematic comparison of jet energy-loss schemes in a realistic hydrodynamic medium

Abstract

We perform a systematic comparison of three different jet energy-loss approaches. These include the Armesto-Salgado-Wiedemann scheme based on the approach of Baier-Dokshitzer-MuellerPeigne-Schiff and Zakharov (BDMPS-Z/ASW), the Higher Twist approach (HT) and a scheme based on the approach of Arnold-Moore-Yaffe (AMY). In this comparison, an identical medium evolution will be utilized for all three approaches: not only does this entail the use of the same realistic three-dimensional relativistic fluid dynamics (RFD) simulation, but also includes the use of identical initial parton-distribution functions and final fragmentation functions. We are, thus, in a unique position, not only to isolate fundamental differences between the various approaches, but also to make rigorous calculations for different experimental measurements using "state of the art" components. All three approaches are reduced to a version which contains only one free tunable parameter, this is then related to the well known transport parameterq. We find that the parameters of all three calculations can be adjusted to provide a good description of inclusive data on RAA versus transverse momentum. However, we do observe slight differences in their predictions for the centrality and azimuthal angular dependence of RAA vs. pT . We also note that the value of the transport coefficientq in the three approaches to describe the data differs significantly.

Parton energy loss in heavy-ion collisions via direct-photon and charged-particle azimuthal correlations

“…The medium properties are extracted through the comparison of measured observables with theoretical models. Many perturbative quantum chromodynamics (pQCD)-based models of parton energy loss have successfully described much of the high-p T data, but the extracted medium parameters span a wide range [3]. In addition to the properties of the medium itself, the amount of energy loss ( E) of a parton propagating through the QCD medium can depend on several factors including E, L, C R , and f , where E is the initial energy of the parton, L is the path length of the parton through the medium, C R is the Casimir (color charge) factor, and f is the quark flavor (of which the mass can affect the amount of energy loss).…”

Full Jet Reconstruction in Heavy Ion Collisions

“…However, these measurements of jet fragmentation particles are biased towards the population of jets that has the least interaction with the medium. Models with a wide range of parameters are able to describe the measurements of di-hadron correlation and nuclear modification factors, leading to limited constraints upon the underlying physics [4,5,6]. Full exploration of jet quenching can be performed only when the geometric biases in measurements of A+A collisions are overcome.…”

Systematic theoretical uncertainties in jet quenching due to gluon kinematics

“…While this paper does not quantify the uncertainties associated with the collinear approximation for other pQCD radiative energy loss models [23,27,34,35], the uncertainties in those models are almost certainly similar to the results quoted here. In particular, the sizable discrepancies between the extracted medium properties obtained by different energy loss groups [8,9,36] are probably within the current theoretical systematic uncertainty.…”

“…One of the great debates over the past several years has been the so-called "discrepancy" of extracted medium parameters from the four energy loss models. An oversimplified description would be that the densities found when comparing energy loss models based on the four pQCD formalisms mentioned in the Introduction (GLV, BDMPS-Z-ASW, HT, AMY) differ by a factor of ∼4-5 [8,9,36]. It is natural and right to begin any calculation with assumptions about the relevant and irrelevant physics of the problem.…”

“…We emphasize that we are interested in quantifying the systematic theoretical uncertainty due to the approximations made in the process of deriving an energy loss formula within any current pQCDbased formalism; we do not focus on the differences due to the various physics assumptions that go into the different formalisms (this is the purview of, e.g., Ref. [36]). In this work we focus quantitatively on the opacity expansion approach; see Fig.…”