Energy dependence of polarized γγ→e+e- in peripheral Au+Au collisions at sNN =54.4 and 200 GeV with the STAR experiment at RHIC

We report the differential yields at mid-rapidity of the Breit-Wheeler process (γγ→e+e-) in peripheral Au+Au collisions at sNN=54.4 and 200 GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC), as a function of energy sNN, e+e- transverse momentum pT, pT2, invariant mass Mee, and azimuthal angle. In the invariant mass range of 0.4<Mee<2.6GeV/c2 at low transverse momentum (pT<0.15GeV/c), the yields increase while the pair (pT2) decreases with increasing sNN, a feature that 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.