Abstract

We report results from the ALICE collaboration on jet production and jet properties in pp and Pb-Pb collisions at the LHC. The charged particle jet production cross-section and measurements of jet fragmentation and jet shape in pp collisions at = 7 TeV are presented. The results are confronted with simulations from Monte Carlo event generators. Measurements of charged particle jets in Pb-Pb collisions at = 2.76 TeV with resolution parameter R = 0.2 and R = 0.3 show a strong momentum dependent suppression in central relative to peripheral collisions. The analysis of the semi-inclusive distribution of charged particle jets recoiling from a high-pT trigger hadron allows an unbiased measurement of the jet structure for larger cone radii. No significant redistribution of the energy flow inside the jet cone is observed. Di-hadron correlations allow to assess jet structure at very low particle momenta. For 2 < pT,trig < 3 GeV/c and 1 < PT,assoc < 2 GeV/c, a strongly asymmetric near-side correlation, broader in Δη than Δϕ, is observed.

Highlights

  • Jets are collimated sprays of particles associated with hard-scattered partons

  • We report results from the ALICE collaboration on jet production and jet properties in pp and Pb-Pb collisions at the LHC

  • Interactions with the medium result in collisional energy loss and give rise to additional induced radiation, which emitted at small angles inside the jet cone can lead to a broadening of the jet profile

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Summary

Introduction

Jets are collimated sprays of particles associated with hard-scattered partons. The study of jet production and fragmentation allows us to test our understanding of perturbative and nonperturbative aspects of QCD. The coupling between partons and medium at a scale of the order of the initial parton energy may be weak, governed by perturbative dynamics. Empirical observations suggest that the thermal scale is relevant for the parton energy loss [2]. It has been predicted, that the coupling of jet fragments to the longitudinally flowing medium [3] or to turbulent color fields [4] will lead to broadening that is larger in pseudorapidity η than azimuthal angle φ (excentric jets).

Results from pp collisions
N coll
10-4 Reference trigger hadron
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