Speaker
Description
The Lorentz-boosted electromagnetic field, arising from colliding nuclei, can be treated as a flux of quasi-real photons. Consequent photonuclear ($\propto$ $Z^{2}$) and photon-photon ($\propto$ $Z^{4}$) processes could reasonably explain the observed enhancements of $J/\psi$ and $e^{+}e^{-}$ pair production at very low transverse momenta ($p_{T}$) in peripheral heavy-ion collisions. The STAR experiment collected datasets of $^{96}_{44}\mathrm{Ru}$+$^{96}_{44}\mathrm{Ru}$ and $^{96}_{40}\mathrm{Zr}$+$^{96}_{40}\mathrm{Zr}$ collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV in 2018, which provide a unique opportunity to study the field strength dependence of photon-induced processes.
In this presentation, we will present measurements of $J/\psi$ and $e^{+}e^{-}$ pair production at very low $p_{T}$ in peripheral and ultra-peripheral isobaric collisions, and study the electromagnetic field dependence of photon-induced production by comparing measurements between isobaric and Au+Au collisions. Physics implications of these results will be discussed together with model comparisons.
