Measurement of jet radial profiles in Pb–Pb collisions at TeV

The jet radial structure and particle transverse momentum (${p}_{T}$) 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 $|{\eta }_{\mathrm{ch jet}}|<0.6$ for transverse momenta ${p}_{T,\phantom{\rule{0.2em}{0ex}}\mathrm{ch jet}}=30$–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 ${p}_{T,\mathrm{assoc}}$-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-${p}_{T}$ associate particles ($4<{p}_{T,\mathrm{assoc}}<20$ 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-${p}_{T}$ associate particles are slightly more collimated in Pb–Pb collisions compared to the reference, while low-${p}_{T}$ associate particles tend to be broadened. The results, which are presented for the first time down to ${p}_{T,\phantom{\rule{0.2em}{0ex}}\mathrm{ch jet}}=30$ 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 ${p}_{T}$, and add further support for the established picture of in-medium parton energy loss.