Azimuthal anisotropy of charged jet production in $\sqrt{s_{\rm NN}}$ = 2.76 TeV Pb-Pb collisions

TL;DR

This paper measures the azimuthal anisotropy of charged jet production in lead-lead collisions at 2.76 TeV, revealing significant elliptic flow signals and comparing results with theoretical models.

Contribution

It provides the first detailed measurement of charged jet azimuthal anisotropy relative to the event plane in heavy-ion collisions, including data correction methods and model comparisons.

Findings

Significant non-zero $v_2^{ ext{ch jet}}$ observed in semi-central collisions.

Azimuthal dependence similar for charged-only and charged+neutral jets.

Data agrees well with JEWEL event generator predictions.

Abstract

We present measurements of the azimuthal dependence of charged jet production in central and semi-central $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as $v_{2}^{\mathrm{ch~jet}}$. Jet finding is performed employing the anti-$k_{\mathrm{T}}$ algorithm with a resolution parameter $R$ = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero $v_{2}^{\mathrm{ch~jet}}$ is observed in semi-central collisions (30-50\% centrality) for 20 $<$ $p_{\mathrm{T}}^{\rm ch~jet}$ $<$ 90 ${\mathrm{GeV}\kern-0.05em/\kern-0.02em c}$. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the $v_2$ of single charged particles at high $p_{\mathrm{T}}$. Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions.