Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR

We present a summary of recent photoproduction results in ultra peripheral relativistic heavy ions collisions with STAR. These collisions have impact parameters larger then twice the nuclear radius; the nuclei do not physically collide, but interact via long-range electromagnetic fields. We observe exclusive ρ⁰ production as well as AuAu → Au^*Au^*ρ⁰ with accompanying mutual nuclear excitation at sqrt(s_{N N}) = 200 GeV. We report the ρ⁰ production cross section for both coherent and incoherent coupling accompanied by mutual nuclear excitation. We have studied the cross section as a function of p_T, y_ρ0 and M_ππ and compared it to theoretical models. In addition, we measured the ρ⁰ helicity matrix elements. They are found to be consistent with s-channel helicity conservation. The ratio of coherent ρ⁰ and direct π⁺π^- pair photoproduction has been measured and found to be consistent with earlier measurements. The 4-pion final state AuAu → π⁺π^-π⁺π^- state has also been observed.