English

Energy Dependence of Polarized $\mathbf{\gamma\gamma\rightarrow e^{+}e^{-}}$ in Peripheral Au+Au Collisions at RHIC

Nuclear Experiment 2024-07-23 v1 High Energy Physics - Experiment

Abstract

We report the differential yields at mid-rapidity of the Breit-Wheeler process (γγe+e\gamma\gamma\rightarrow e^{+}e^{-}) in peripheral Au+Au collisions at sNN=\sqrt{s_{_{\rm{NN}}}} = 54.4 GeV and 200 GeV with the STAR experiment at RHIC, as a function of energy sNN\sqrt{s_{_{\rm{NN}}}}, e+ee^{+}e^{-} transverse momentum pTp_{\rm T}, pT2p_{\rm T}^{2}, invariant mass MeeM_{ee} and azimuthal angle. In the invariant mass range of 0.4 << MeeM_{ee} << 2.6 GeV/c2c^{2} at low transverse momentum (pTp_{\rm T} < < 0.15 GeV/cc), the yields increase while the pair pT2\sqrt{\langle p_{\rm T}^{2} \rangle} decreases with increasing sNN\sqrt{s_{_{\rm{NN}}}}, a feature is correctly predicted by the QED calculation. The energy dependencies of the measured quantities are sensitive to the nuclear form factor, infrared divergence and photon polarization. The data are compiled and used to extract the charge radius of the Au nucleus.

Keywords

Cite

@article{arxiv.2407.14821,
  title  = {Energy Dependence of Polarized $\mathbf{\gamma\gamma\rightarrow e^{+}e^{-}}$ in Peripheral Au+Au Collisions at RHIC},
  author = {The STAR Collaboration},
  journal= {arXiv preprint arXiv:2407.14821},
  year   = {2024}
}