Mainz 2022 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 57: Heavy-Ion Collisions and QCD Phases XII

HK 57.4: Talk

Thursday, March 31, 2022, 14:45–15:00, HK-H2

Direct photons in high-multiplicity pp collisions with dielectrons in ALICE — •Ivan Vorobyev for the ALICE collaboration — Technische Universität München

Low-mass e⁺e⁻ pairs produced in ultra-relativistic heavy-ion collisions at the LHC carry important information about the system space-time evolution unperturbed by strong final-state interactions. The dielectron continuum is very rich in physics sources: on top of Dalitz and resonance decays of pseudo-scalar and vector mesons, thermal black-body radiation contains the information about the temperature of the hot and dense system created in heavy-ion collisions. In proton–proton (pp) collisions, measurement of direct photons serves as a fundamental test for perturbative QCD calculations and as a baseline for the studies in heavy-ion collisions. Recently, pp collisions with high charged-particle multiplicities have been found to exhibit interesting phenomena resembling some observations done in heavy-ion collisions. Low-mass dielectrons could provide additional information regarding the underlying physics processes in such collisions.

We present the latest results from the dielectron analysis of large data sample of pp collisions at √s = 13 TeV collected with ALICE during the LHC Run 2. A particular focus of the discussion is put on the production of direct photons in pp collisions collected with a trigger on high charged-particle multiplicities. The relative increase of dielectron production in high-multiplicity events with respect to all inelastic collisions is compared to the expectations from already measured multiplicity-dependent production of light and heavy hadrons.