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Title: Dielectron production in central Pb-Pb collisions at sNN=5.02TeV
The first measurement of the e + e pair production at midrapidity and low invariant mass in central Pb-Pb collisions at s N N = 5.02 TeV at the Large Hadron Collider is presented. The yield of e + e pairs is compared with a cocktail of expected hadronic decay contributions in the invariant mass ( m e e ) and pair transverse momentum ( p T , e e ) ranges m e e < 3.5 GeV / c 2 and p T , e e < 8 GeV / c . For 0.18 < m e e < 0.5 GeV / c 2 the ratio of data to the cocktail of hadronic contributions amounts to 1.40 ± 0.11 ( stat . ) ± 0.23 ( syst . ) ± 0.16 ( cocktail ) and 1.42 ± 0.11 ( stat . ) ± 0.23 ( syst . ) 0.29 + 0.24 ( cocktail ) , including or not including medium effects in the estimation of the heavy-flavor background, respectively. It is consistent with predictions from two different models for an additional contribution of thermal e + e pairs from the hadronic and partonic phases. In the intermediate-mass range ( 1.2 < m e e < 2.6 GeV / c 2 ), the pair transverse impact parameter of the e + e pairs ( DCA e e , where “DCA” denotes “distance of closest approach”) is used for the first time in Pb-Pb collisions to separate displaced dielectrons from heavy-flavor hadron decays from a possible (thermal) contribution produced at the interaction point. The data are consistent with a suppression of e + e pairs from c c ¯ and an additional prompt component. Finally, the first direct-photon measurement in the 10% most central Pb-Pb collisions at s N N = 5.02 TeV is reported via the study of virtual direct photons in the transverse momentum range 1 < p T < 5 GeV / c . A model including prompt photons, as well as photons from the preequilibrium and fluid-dynamic phases, can reproduce the result, while being at the upper edge of the data uncertainties.  more » « less
Award ID(s):
2208883
PAR ID:
10689729
Author(s) / Creator(s):
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Corporate Creator(s):
Publisher / Repository:
https://journals.aps.org
Date Published:
Journal Name:
Physical Review C
Volume:
112
Issue:
5
ISSN:
2469-9985
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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