A Monte Carlo study of jet fragmentation functions in PbPb and pp collisions at sqrt{s}=2.76 TeV

Abstract

The parton-to-hadron fragmentation functions (FFs) obtained from the YAJEM and PYTHIA6 Monte Carlo event generators, are studied for jets produced in a strongly-interacting medium and in the QCD "vacuum" respectively. The medium modifications are studied with the YAJEM code in two different scenarios by (i) accounting for the medium induced virtuality ∆Q 2 transferred to the leading parton from the medium, and (ii) by altering the infrared sector in the Borghini-Wiedemann approach. The results of our simulations are compared to experimental jet data measured by the CMS experiment in PbPb and pp collisions at a center-ofmass energy of 2.76 TeV. Though both scenarios qualitatively describe the shape and main physical features of the FFs, the ratios are in much better agreement with the first scenario. Results are presented for the Monte Carlo FFs obtained for different parton flavours (quark and gluon) and accounting exactly, or not, for the experimental jet reconstruction biases.

Jet fragmentation functions in proton-proton collisions using soft-collinear effective theory

“…The numbers in square brackets correspond to different jet transverse momentum bins, e.g. [25,40] while the solid blue curves are the "nominal" theoretical calculations, where we make the scale choices µ = p T , µ G = µ J = p T R defined in the last section. The green bands are the estimated uncertainties of our theoretical calculations from the scale variations for all three scales µ, µ G , µ J by a factor of 2 around the above central values.…”

“…For recent experimental measurements of the jet fragmentation function in heavy ion collisions at the LHC, see [16][17][18]. For some theoretical work along this direction, see [25][26][27].…”

The angular structure of jet quenching within a hybrid strong/weak coupling model

“…[70][71][72][73][74][75] for reviews.) Based on these approaches, Monte Carlo tools for analyzing jet observables are being developed [76][77][78][79][80][81][82][83] and many phenomenological studies of jets in medium have been confronted with LHC measurements of a variety of jet observables , including intrajet observables like those that we shall focus on [85,89,99,101,104,[106][107][108][109].…”

On jet structure in heavy ion collisions

“…Jet fragmentation function was calculated and compared with the data in Refs. [34,42,66,67]. JEWEL event generator [34] and hybrid strong/weak coupling jet quenching model [42] are successful in describing the basic trends seen in the data excepting low-p T region.…”

“…Effective 1+1 dimensional quasi-Abelian model [66] is able to reproduce low and intermediate p T -region, and predicts unmodified fragmentation at high p T . Jet fragmentation function [67] and jet shapes [58] were studied also with YaJEM event generator. It has been found that YaJEM results are qualitatively consistent with measurements of jet fragmentation function, while simulated jet broadening seems to be significantly stronger than in the data.…”