QM 2022

Collision species and beam energy dependences of photon-induced lepton pair production at STAR

7 Apr 2022, 10:20

20m

large aula A (Auditorium Maximum UJ)

Oral presentation Ultra-peripheral collisions Parallel Session T09: Ultra-peripheral collisions

Speaker

Xiaofeng Wang (Shandong University)

Description

Ultra-strong electromagnetic field can generate a large flux of quasi-real photons arising from the Lorentz-contraction and the large electric charge (Z) of heavy nuclei colliding at ultra-relativistic speeds. These ultra-strong fields can be studied through dileptons ($e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$) and vector mesons ($J/\psi$) produced via photon-photon and photonuclear processes, respectively, in which the photon flux is proportional to $Z^2$. In particular, the photo-produced dileptons carry information about the strength and spatial distribution of the colliding fields. Therefore, they provide a novel tool to test the spatial and polarization dependent effects predicted by QED for vacuum birefringence and the Breit-Wheeler process.

In this talk, we present the first investigation of impact parameter and collision species dependences of dilepton and $J/\psi$ photo-production in isobaric collisions (${}_{44}^{96}Ru$ + ${}_{44}^{96}Ru$, ${}_{40}^{96}Zr$ + ${}_{40}^{96}Zr$) at $\sqrt{s_{\mathrm{NN}}}=$ 200 GeV. The collision energy dependence of these photo-production processes is further studied in peripheral Au+Au collisions with measurements at $\sqrt{s_{\mathrm{NN}}}=$ 54.4 GeV and 200 GeV. We discuss the physics implications of these results and compare them to models.

Presentation materials

QM2022_XiaofengWang.pdf