In:
Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2023, No. 6 ( 2023-06-05)
Abstract:
The first measurement of the e + e − pair production at low lepton pair transverse momentum ( p T , ee ) and low invariant mass ( m ee ) in non-central Pb–Pb collisions at $$ {\sqrt{s}}_{\textrm{NN}} $$ s NN = 5 . 02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity ( |η e | 〈 0 . 8) as a function of invariant mass (0.4 ≤ m ee 〈 2 . 7 GeV/ c 2 ) in the 50–70% and 70–90% centrality classes for p T , ee 〈 0.1 GeV/ c , and as a function of p T , ee in three m ee intervals in the most peripheral Pb–Pb collisions. Below a p T , ee of 0.1 GeV/ c , a clear excess of e + e − pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The m ee excess spectra are reproduced, within uncertainties, by different predictions of the photon–photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the p T , ee spectra. The measured $$ \sqrt{\left\langle {p}_{\textrm{T},\textrm{ee}}^2\right\rangle } $$ p T , ee 2 of the excess p T , ee spectrum in peripheral Pb–Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region.
Type of Medium:
Online Resource
ISSN:
1029-8479
DOI:
10.1007/JHEP06(2023)024
Language:
English
Publisher:
Springer Science and Business Media LLC
Publication Date:
2023
detail.hit.zdb_id:
2027350-2
