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ATLAS Note
Report number	ATL-PHYS-PROC-2015-066
Title	Jet path length dependence in Pb+Pb Collisions with the ATLAS detector
Author(s)	Santos, Helena (LIP, Lisbon)
Corporate Author(s)	The ATLAS collaboration
Imprint	13 Sep 2015. - 4 p.
In:	Nucl. Part. Phys. Proc. 276-278 (2016) 205-208
In:	7th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions, Montreal, Québec, Canada, 29 Jun - 3 Jul 2015, pp.205-208
DOI	10.1016/j.nuclphysbps.2016.05.045
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Free keywords	Heavy Ions ; Elliptic flow ; Dijets ; Multijets ; HEAVYIONS
Abstract	The phenomenon of events containing highly asymmetric dijet pairs is one of the most striking results in heavy ion physics. It has provided the first direct observation of in-medium jet energy loss at the LHC. New results showing the variation of the dijet asymmetry with the angle between the leading jet and the second order event-plane are presented. This observable effectively probes the path-length dependence of the dijet asymmetry at fixed centrality. The variation of the dijet asymmetry with the soft particle v2, at fixed centrality is also measured. These measurements can provide a better understanding of the correlation of the parton energy-loss with the underlying geometry. Correlated production of nearby jets is also shown. Two neighbouring jets originating from the same hard scattering should have more similar path lengths in the medium compared to the two jets in the dijet event topology, therefore measuring neighbouring jets may probe differences in quenching that do not result from different path length. The production of nearby jets is quantified using the rate, R_DeltaR, of “neighbouring” jets that accompany “test” jets within a given range of angular distance in the pseudorapidity-azimuthal angle plane. The centrality dependence of R_DeltaR as well as the ratios of the R_DeltaR values in collisions of different centrality and the values in the 40–80% centrality range are presented.
Copyright/License	Preprint: (License: CC-BY-4.0)

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