Dielectron production at low transverse momentum in Pb-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV with ALICE

TL;DR

This paper analyzes dielectron production at low transverse momentum in Pb-Pb collisions at 5.02 TeV, revealing an excess in peripheral collisions consistent with coherent photon-photon interactions.

Contribution

It provides the first detailed measurement of low-$p_{T,ee}$ dielectron spectra in Pb-Pb collisions at this energy, highlighting the excess in peripheral collisions attributed to coherent photo-production.

Findings

Data fit expected spectrum in central collisions dominated by heavy-flavour decays.

Peripheral collisions show an excess at low $p_{T,ee}$ beyond hadronic and thermal sources.

The excess is compatible with coherent photon-photon interaction models.

Abstract

Dielectrons probe a wide range of phenomena in heavy-ion collisions. These include light- and heavy-flavour meson production, thermal radiation and coherent photo-production. The latter process is distinguished by dielectron production at low transverse-pair momentum ($ \it{p}_{\textrm{T,ee}}$). Transverse momentum spectra of dielectrons in central and peripheral Pb-Pb collisions are extracted and compared to the corresponding expectations. In central collisions the data fit the expected spectrum, which is dominated by semi-leptonic decays of correlated heavy-flavour hadrons. In peripheral collisions, the data exhibit an excess at low \ptee with respect to hadronic and thermal sources. The observed excess yield is compatible with calculations for dielectron production from coherent photon-photon interactions.