Speaker
Description
Dileptons ($l^{+}l^{-}$) are produced throughout all stages of heavy-ion collisions and escape with minimum interaction with the strongly interacting medium. For this reason, $l^{+}l^{-}$ pair measurements play an essential role in the study of the hot and dense nuclear matter created in heavy-ion collisions. Dileptons in the low invariant mass region (up to M$_{ll}\sim$1~GeV/c$^2$) retain information about the in-medium modification of vector mesons while dileptons in the intermediate mass region (extending out to M$_{ll}\sim$3 GeV/c$^2$) predominantly originate from charm decays and thermal radiation of the medium. At higher invariant masses, recent studies of $J/\psi$ yields in peripheral A$+$A collisions by the ALICE~\cite{alice} and STAR collaborations showed significant excess at very low momentum transfers (p$_T$ $<$ 0.3~GeV/c). These observations may point to evidence of coherent photoproduction of $J/\psi$ in hadronic interactions which conflicts with traditional knowledge of the coherent photoproduction mechanism. It is interesting to investigate the $e^{+}e^{-}$ pair production in a wider invariant mass region (M$_{ee}<$4 GeV/c$^2$) at very low p$_T$ in heavy-ion collisions for different centrality bins in order to study the production mechanism.
This talk will cover $e^{+}e^{-}$ spectra with various invariant mass and p$_{T}$ differentials in Au$+$Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and U$+$U collisions at $\sqrt{s_{NN}}$ = 193 GeV. The structure of the t (t = p$_{T}^{2}$ ) distributions of these mass regions will be shown and compared with the same distributions in ultra-peripheral collisions. Additionally, this talk will cover first measurements of $\mu^{+}\mu^{-}$ invariant mass spectra from STAR's recently installed Muon Telescope Detector (MTD) in p$+$p and Au$+$Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Physics implications of the $\mu^{+}\mu^{-}$ results will be discussed in the context of STAR's published $e^{+}e^{-}$ results.
| Preferred Track | Electromagnetic Probes |
|---|---|
| Collaboration | STAR |
