Speaker
Description
The strong electromagnetic field generated by the colliding nuclei in heavy-ion collisions can be represented by a spectrum of photons leading to photon-induced interactions. While such interactions are traditionally studied in ultra-peripheral collisions (UPC) without any nuclear overlap, significant enhancements of dilepton pairs and J/$\psi$ production at very low transverse momentum ($p_{\rm T}$ < 0.2 GeV/c) above the expected hadronic interaction yields have been observed experimentally in non-UPC events via the $e^+e^-$ channel. The observed excess yields exhibit a much weaker centrality dependence compared to the hadronic production and are consistent with photon-induced interactions. The measurements of very low $p_{\rm T}$ vector meson and dilepton production in peripheral heavy-ion collisions provide a unique opportunity to study photoproduction in collisions with well-defined and smaller impact parameters compared to that of UPC.
In 2014 and 2016, the STAR experiment recorded large samples of Au+Au collisions at $\sqrt{s_{{\rm NN}}}$ = 200 GeV. In this presentation, we will present new measurements of very low $p_{\rm T}$ dilepton and J/$\psi$ production in peripheral Au+Au collisions via the $\mu^+\mu^-$ channel using these datasets. These measurements are complementary to the previous dielectron results. Distributions of invariant mass, $p_{\rm T}^{2}$, and nuclear modification factor will be shown. Physics implications will also be discussed together with model comparisons.
