SMuK 2021 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 22: Heavy-Ion Collisions and QCD Phases IV

HK 22.4: Talk

Thursday, September 2, 2021, 17:30–17:45, H1

Direct Photon Production in pp collisions at √s = 13 TeV as a Function of Multiplicity with ALICE — •Ilya Fokin für die ALICE Kollaboration — Physikalisches Institut, Universität Heidelberg, Heidelberg, Germany

Thermal direct photons are a sign of the production of a quark-gluon-plasma (QGP). They have been measured in PbPb collisions by ALICE while measurements in pp collisions showed no enhancement over the decay photon cocktail. Some collective effects, which could be explained by a QGP, such as long-range two-particle correlations have been observed not only in heavy-ion collisions, but also in high-multiplicity pp collisions. An enhancement of the direct photon production at low transverse momentum in high-multiplicity collisions compared to low-multiplicity collisions would suggest the creation of a QGP also in pp collisions.

In this talk, a measurement of the direct photon production in pp collisions at 13 TeV as a function of the charged particle multiplicity with ALICE is presented. Photons are reconstructed using the photon conversion method, relying on pair conversions in the detector material. π⁰ and η mesons are reconstructed via their two-photon decay channels for the calculation of the decay photon cocktail.