Measurement of jet radial profiles in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

Abstract

The jet radial structure and particle transverse momentum ($p_{\mathrm{T}}$) composition within jets are presented in centrality-selected Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. Track-based jets, which are also called charged jets, were reconstructed with a resolution parameter of $R=0.3$ at midrapidity $|{\eta }_{\mathrm{ch}\mathrm{jet}}|<0.6$ for transverse momenta $p_\rm{T,\,ch\,jet}=30$-$120$ GeV/$c$. Jet-hadron correlations in relative azimuth and pseudorapidity space ($\Delta \phi$, $\Delta \eta$) are measured to study the distribution of the associated particles around the jet axis for different $p_\rm{T, assoc}$-ranges between 1 and 20 GeV/$c$. The data in Pb-Pb collisions are compared to reference distributions for pp collisions, obtained using embedded PYTHIA simulations. The number of high-$p_{\mathrm{T}}$ associate particles ($4<p_\rm{T, assoc}<20$ GeV/$c$) in Pb-Pb collisions is found to be suppressed compared to the reference by 30 to 10%, depending on centrality. The radial particle distribution relative to the jet axis shows a moderate modification in Pb-Pb collisions with respect to PYTHIA. High-$p_{\mathrm{T}}$ associate particles are slightly more collimated in Pb-Pb collisions compared to the reference, while low-$p_{\mathrm{T}}$ associate particle tend to be broadened. The results, which are presented for the first time down to $p_\rm{T,\,ch\,jet}=30$ GeV/$c$ in Pb-Pb collisions, are compatible with both previous jet-hadron-related measurements from the CMS Collaboration and jet shape measurements from the ALICE Collaboration at higher $p_{\mathrm{T}}$, and add further support for the established picture of in-medium parton energy loss.

30 pages, 5 captioned figures, 4 tables, authors from page 23, published version, figures at http://alice-publications.web.cern.ch/node/5247

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