Speaker
Description
Electromagnetic probes such as photons and dielectrons (e$^{+}$e$^{-}$ pairs) are a unique tool to study the space-time evolution of the hot and dense matter created in ultra-relativistic heavy-ion collisions. They are produced at all stages of the collision with negligible final-state interactions. At intermediate dielectron invariant mass ($m_{\rm ee} > 1$ GeV/$c^{2}$), thermal radiation from the quark-gluon plasma carries information about the early temperature of the medium. At LHC energies, it is however dominated by a large background from correlated heavy-flavour hadron decays. At smaller $m_{\rm ee}$, thermal radiation from the hot hadronic phase contributes to the dielectron spectrum via decays of $\rho$ mesons, whose spectral function is sensitive to chiral-symmetry restoration. Finally, at vanishing $m_{\rm ee}$, the real direct photon fraction can be extracted from the dielectron data. In pp collisions, such measurement in minimum bias events serves as a baseline and a fundamental test for perturbative QCD calculations, while studies in high charged-particle multiplicity events allow one to search for thermal radiation in small colliding systems. The latter show surprising phenomena similar to those observed in heavy-ion collisions.
In this talk, final ALICE results, using the full data sample collected during the LHC Run 2, will be presented. They include measurements of the dielectron and direct-photon production in central Pb--Pb at the centre-of-mass energy per nucleon pairs, $\sqrt{s_{\rm NN}}$, of 5.02 TeV, as well as of direct photons in minimum bias and high-multiplicity pp collisions at $\sqrt{s} = 13$ TeV. Finally, first results with the Run 3 pp data at $\sqrt{s} = 13.6$ TeV, using the upgraded ALICE detector to disentangle the different dielectron sources, will be reported.
| Category | Experiment |
|---|---|
| Collaboration (if applicable) | ALICE |
