Ultra-peripheral collisions in STAR

Ultra-relativistic heavy ions generate strong electromagnetic fields, which
offer the opportunity to study exclusive photon-photon and photon-nucleus processes at RHIC
in ultra-peripheral collisions (UPC). While exclusive photoproduction of vector
mesons is sensitive to the gluon distribution of the interacting target nucleus,
photoproduction of light vector mesons is also a probe to photon-pomeron coupling.
Exclusive production of lepton pairs in the photon-photon interactions provides
a test to quantum electrodynamics with a large coupling constant.

We present STAR measurements on light $\rho^0$ mesons and heavy $J/\psi$ mesons
in photon-nucleus processes
and exclusive electron-positron pair production in photon-photon processes
in Au+Au UPC at $\sqrt{s_{NN}}$ = 200 GeV.
The photoproduction processes
are tagged at the trigger level by forward neutrons emitted by mutual
Coulomb excitations of interacting nuclei.
All these measurements are performed
at central rapidities of about $|y|<1$.