Abstract
We report the measurements of e+e- pair production at very low e+e- pair transverse momentum (pT < 0.15 GeV/c) in Au+Au collisions at [see formula in PDF] = 200 GeV and U+U collisions at [see formula in PDF] = 193 GeV using the STAR detector at the Relativistic Heavy Ion Collider. In 60-80% centrality, significant excesses are observed with respect to hadronic cocktails in both Au+Au and U+U collisions. These excess yields can not be explained by a theoretical model calculation incorporating in-medium broadened ρ spectral function. Additionally, the [see formula in PDF] distribution for excess yield is shown and found to be exponential at very low pT.
Highlights
The e+e− pair production provides a unique observable to study the fundamental properties of the hot and dense medium created in ultra-relativistic heavy-ion collisions
80% centrality Au+Au and U+U collisions, there are significant excesses observed with respect to the corresponding hadronic cocktails [5]
Compared to those in 60-80% centrality, the enhancement factors in 40-60% are less significant while in 10-40% the data are consistent with the hadronic cocktail within uncertainties for Mee > 0.76 GeV/c2
Summary
The e+e− pair production provides a unique observable to study the fundamental properties of the hot and dense medium created in ultra-relativistic heavy-ion collisions Those pairs are produced during all stages of the collisions and from all forms of the created matter. YaonireadltdRiUoeinnc+eapnUlsetolrcyipo,ohltblheissereiaroAlvnePLsdbIaCs+tiEm√PcisbloNalcrNlaobb=leloihs1raia9ovt3inioosGnraefrtVoepr√aoJstr/NψtpeNTdin=
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