May 13 – 19, 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

Analysis of the apparent nuclear modification in peripheral 5.02 TeV Pb-Pb collisions with ALICE

May 15, 2018, 10:20 AM
Sala Perla, 1st Floor (Palazzo del Casinò)

Sala Perla, 1st Floor

Palazzo del Casinò

Parallel Talk Jet modifications and high-pT hadrons Jet modifications and high-pT hadrons


Michael Linus Knichel (CERN)


We present charged particle spectra at midrapidity measured in lead-lead collisions at a center-of-mass energy per nucleon pair of 5.02 TeV with ALICE, in twenty centrality classes ranging from most central (0-5%) to very peripheral (95-100%) collisions. At high transverse momentum ($8 < p_{\rm T} <30$ GeV/$c$), the average nuclear modification factor ($R_{\rm AA}$) is found to increase from 0-5% central to 75-85% peripheral collisions, beyond which it strongly falls to very low values for the most peripheral collisions (95-100%). Our findings support the idea that peripheral collisions are affected by biases caused by the event selection and collision geometry, which can lead to an apparent nuclear modification in peripheral collisions even in the absence of jet quenching. The results in peripheral collisions are consistent with a PYTHIA-based model without nuclear modification. Our study provides an explanation of the observation that $R_{\rm AA}$ is lower than unity in peripheral Pb-Pb collisions, but equal to one in p-Pb collisions at similar charged particle multiplicity.

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Collaboration ALICE
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