Quenching of Hadron Spectra in Heavy Ion Collisions at the LHC

Abstract

The p ⊥ dependence of the nuclear modification factor R AA measured in PbPb collisions at the LHC exhibits a universal shape, which can be very well reproduced in a simple energy loss model based on the BDMPS medium-induced gluon spectrum. We update a former study by including in the analysis the recent CMS measurements on J/ψ production in PbPb collisions at √ s = 5.02 TeV and charged hadron production in XeXe collisions at √ s = 5.44 TeV. The average parton energy loss extracted from minimum bias XeXe collisions is reduced typically by 20% compared to PbPb collisions, consistent with a length dependence ε ∝ L 1.3±0.5 with L ∝ A 1/3 .

Intensity of gluon bremsstrahlung in a finite plasma

“…The second contribution represents the collisional distribution in case of collision. It can be shown to satisfy a Moliere's transport equation whose solution reads Σ 2 (q, δz) = d 2 xe −iq•x e −n0δzσgq e n0(z)δzσgq(|x|) − 1 , (13) and where the Fourier transform of the squared single elastic amplitude reads at first order in the coupling…”

“…Semi-infinite medium calculations of this phenomenon under the Fokker-Planck approximation have been introduced for QED in [4,5] and subsequent extensions for QCD [6][7][8] have been developed. These results [9][10][11][12][13] have been formulated to account for the energy-loss mechanism originating the depletion of high transverse momentum particles in heavy ion collisions at RHIC and LHC due to a multiple scattering process with a medium, an indicative sign of QGP formation [14]. We have to note, however, that in the Fokker-Planck approximation, which naturally emerges when the number of collisions is large, the medium interaction is replaced by an effective one [6,7].…”

Recent Results from ATLAS: Onia, Heavy-Flavor, and More

“…While the strong suppression of quarkonia in nucleus-nucleus collisions is firmly established experimental fact, its interpretation remains open. Besides initial state effects and the interaction with co-moving hadrons, which are discussed in the context of p+Pb measurements in Section 2, it is also the parton energy loss which was recently suggested as an alternative physics mechanism for the observed quarkonia suppression [3,4]. To help address the origin of the quarkonium suppression, ATLAS published a measurement [5] of prompt charmonia, originating from the formation of cc bound state which follows immediately after the hard process, and non-prompt charmonia, originating from b-hadron decays.…”

HQ Collisional energy loss in a magnetized medium

“…It is well known that a high energy particle created in the initial stages of the heavy ion collision loses its energy in the medium by interacting with the medium partons. This leads to the phenomena of jet quenching, which as anticipated many years ago, is one of the prominent probes of QGP [47][48][49][50]; for a recent review see Ref. [51].…”