Quark Matter 2017

Dilepton production in p+p, Au+Au collisions at sNN=200 GeV and U+U collisions at sNN=193 GeV

7 Feb 2017, 08:30

20m

Regency C

Oral Electromagnetic Probes Parallel Session 1.3: Electromagnetic Probes (I)

Speaker

James Brandenburg (Rice University)

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.

Presentation materials

jdb_QM17.pdf