Speaker
Description
Dielectron production can occur in ultraperipheral heavy ion collisions (UPCs) via the Breit-Wheeler process, in which the quasi-real photons from the heavy ion-induced electromagnetic fields interact to produce a low transverse momentum dielectron pair. This production is sensitive to the charge radius and nuclear shape of the atomic nucleus sourcing the photons. By comparing the momentum dependence of the production cross sections in Au+Au and U+U to each other and to lowest-order quantum electrodynamics calculations, sensitivity to differences in nuclear shape and resulting field strength distributions can be studied. \par
We present experimental results for the dielectron production cross sections through the Breit-Wheeler process in U+U and Au+Au UPCs at $\sqrt{s_{NN}}$ = 193 and 200 GeV, respectively, at STAR at pair $p_{T} < 0.25$ GeV/c. We also present comparisons of these results with QED numerical calculations for the predicted cross sections, which allow new constraints on the charge radius and skin depth for the uranium nucleus.
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