Speaker
Shuai Yang
(Brookhaven National Laboratory)
Description
Recently, a significant excess of J/ψ yield at very low transverse momenta (pT<0.3 GeV/c) was reported by the ALICE collaboration in peripheral Pb+Pb collisions at sNN‾‾‾‾√ = 2.76 TeV [1]. STAR collaboration also observed the similar behavior of J/ψ production in peripheral Au+Au collisions at sNN‾‾‾‾√ = 200 GeV and U+U collisions at sNN‾‾‾‾√ = 193 GeV. These observations may point to possibility of an additional process with the coherent photoproduction mechanism. It is also interesting to investigate the e+e− pair production in a wider invariant mass region (Mee<4 GeV/c2) at very low pT in heavy-ion collisions for different centrality bins in order to study the production mechanism.
In this talk, we will present the centrality dependence of e+e− pair invariant mass spectra at very low pT (pT<0.15 GeV/c) in Au+Au collisions at sNN‾‾‾‾√ = 200 GeV and U+U collisions at sNN‾‾‾‾√ = 193 GeV. The pT differentials and t (−t≈p2T) distributions of two mass regions (0.4-0.76 and 1.2-2.6 GeV/c2) in most peripheral aforementioned heavy-ion collisions will be shown and compared with the same distributions in ultra-peripheral collisions. Physics implications will be discussed.
[1] J. Adam et al. (ALICE Collaboration), Phys. Rev. Lett. 116, 222301 (2016).
