Proceedings of Direct photon measurement in small systems and thermal radiation from QGP with ALICE, Hard Probes conference 2024

TL;DR

This paper presents ALICE's measurements of dielectron and direct photon production in small and large systems, providing insights into thermal radiation from QGP and establishing baselines for heavy-ion collision studies.

Contribution

It reports new experimental results on dielectron and photon production in pp and Pb-Pb collisions at 13 TeV, highlighting implications for thermal radiation and QGP presence in small systems.

Findings

Dielectron production measured in pp and Pb-Pb collisions.

Evidence of thermal radiation from QGP in heavy-ion collisions.

Baseline data for small system QGP searches.

Abstract

Electromagnetic probes are a unique tool for studying the space-time evolution of the hot and dense matter created in ultra-relativistic heavy-ion collisions. Dielectrons are emitted during the entire evolution of the medium created in such collisions, allowing the extraction of the real direct photon fraction at vanishing mass and providing access to thermal radiation from the early hot stages of the collision. The measurement of dielectron and direct-photon production in minimum-bias pp collisions serves as a crucial baseline for the studies in heavy-ion collisions, whereas pp collisions with high charged-particle multiplicities allow the search for the possible presence of QGP in small systems. An overview of the final results of dielectron production in pp at $\sqrt{s}=13$ TeV and in central \PbPb collisions at \fivenn measured by ALICE is presented, together with their implications for the production of thermal radiation. Finally, an outlook on future measurements is given with the first performance studies from Run 3.