Resolution effects in the hybrid strong/weak coupling model

Abstract

Within the context of a hybrid strong/weak coupling model of jet quenching, we study the consequences of the fact that the plasma produced in a heavy ion collision cannot resolve the substructure of a collimated parton shower propagating through it with arbitrarily fine spatial resolution. We introduce a screening length parameter, L res , proportional to the inverse of the local temperature in the plasma, estimating a range for the value of the proportionality constant via comparing weakly coupled QCD calculations and holographic calculations appropriate in strongly coupled plasma. We then modify the hybrid model so that when a parton in a jet shower splits, its two offspring are initially treated as unresolved, and are only treated as two separate partons losing energy independently after they are separated by a distance L res . This modification delays the quenching of partons with intermediate energy, resulting in the survival of more hadrons in the final state with p T in the several GeV range. We analyze the consequences of different choices for the value of the resolution length, L res , and demonstrate that introducing a nonzero L res results in modifications to the jet shapes and jet fragmentations functions, as it makes it more probable for particles carrying a small fraction of the jet energy at larger angles from the jet axis to survive their passage through the quark-gluon plasma. These effects are, however, small in magnitude, something that we confirm via checking for effects on missing-p T observables. arXiv:1707.05245v1 [hep-ph]

Measurement of jet fragmentation in Pb+Pb and pp collisions at sNN=5.02 TeV with the ATLAS detector

“…However, the observation for high-z fragments is of limited significance due to the limited size of the available data sample. Figure 25 shows the same ratios for the 0-10% centrality interval compared with calculations from the hybrid model [51] and the effective quenching model [21]. Both calculations are consistent with the data for jets with |y jet | < 1.2 with larger deviations in rapidity interval 1.2 < |y jet | < 2.1.…”

“…19 shows that the enhancement of hard fragments with z 0.3 is nearly independent of p jet T . The fragmentation functions have been calculated within a hybrid model of jet quenching, which uses perturbative techniques for the high-Q 2 processes in jet evolution and strong coupling for the low momentum scales associated with the QGP [50,51]. Within this model, there is a length scale L res which can be interpreted as the minimum distance required to resolve a parton as separate from the others in the showering process when it occurs in the QGP medium.…”

Jets in QCD matter: Monte Carlo approaches

“…This simultaneous description is even more challenging if the jet mass is also considered. Figure 3: Jet Radial profile as given by Coupled Jet-Fluid [12] (upper, left), Hybrid [15] (upper, right), MARTINI [9] (lower, left) and JEWEL [7] (lower, right). The CMS data [32] are also represented as circles in each plot.…”

“…These structures would then radiate as a single charge in the medium, and their angular pattern would follow an anti-angular ordering, as opposed to vacuum radiation. So far, coherence effects were only implemented in the Hybrid approach (see [15]), yielding no effect on the resulting jet modifications (see section 3).…”

Medium response to jets in heavy ion collisions

“…In addition, also the latest version of Hybrid Strong/Weak Coupling model [15,66] contains a simplified description for the medium response. The lost energy and momentum of the jet calculated by N = 4 supersymmetric Yang-Mills theory [67] are stored into a boost-invariant Bjorken fluid as a perturbation, and then the hadrons enhanced by the perturbation are obtained by using the linear expansion of Cooper Frye formula.…”