Holographic Jet Shapes and their Evolution in Strongly Coupled Plasma

Jasmine Brewer,Krishna Rajagopal,Andrey Sadofyev,Wilke Van Der Schee

doi:10.1016/j.nuclphysa.2017.05.016

Abstract

Recently our group analyzed how the probability distribution for the jet opening angle is modified in an ensemble of jets that has propagated through an expanding cooling droplet of plasma [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603]. Each jet in the ensemble is represented holographically by a string in the dual 4+1- dimensional gravitational theory with the distribution of initial energies and opening angles in the ensemble given by perturbative QCD. In [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603], the full string dynamics were approximated by assuming that the string moves at the speed of light. We are now able to analyze the full string dynamics for a range of possible initial conditions, giving us access to the dynamics of holographic jets just after their creation. The nullification timescale and the features of the string when it has nullified are all results of the string evolution. This emboldens us to analyze the full jet shape modification, rather than just the opening angle modification of each jet in the ensemble as in [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603]. We find the result that the jet shape scales with the opening angle at any particular energy. We construct an ensemble of dijets with energies and energy asymmetry distributions taken from events in proton-proton collisions, opening angle distribution as in [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603], and jet shape taken from proton-proton collisions and scaled according to our result. We study how these observables are modified after we send the ensemble of dijets through the strongly-coupled plasma.

Highlights

The discovery that the quark-gluon plasma created in heavy-ion collisions at RHIC and the LHC is strongly coupled has generated immense theoretical interest and leaves many unanswered questions
We construct an ensemble of holographic jets with initial energy and opening angle distributions taken from perturbative QCD, and study how that ensemble is modified after it propagates through an expanding, cooling droplet of strongly coupled plasma
We calculate the jet shape modification between proton–proton and heavy ion collisions, ρ(r)PbPb/ρ(r)pp, from the modification by the plasma compared to the vacuum jet shape

Summary

Introduction

The discovery that the quark-gluon plasma created in heavy-ion collisions at RHIC and the LHC is strongly coupled has generated immense theoretical interest and leaves many unanswered questions. Jets in heavy ion collisions can provide important insights into QCD and the quark-gluon plasma, since they provide access to the interactions of hard partons with the medium and incorporate physics at widely separated momentum scales.

Results

Conclusion