Abstract
We present a measurement of photonuclear production in ultraperipheral collisions at GeV from the STAR experiment. The final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The invariant mass spectrum of the coherent events exhibits a broad peak around with a width of , in agreement with the photoproduction data for the . We do not observe a corresponding peak in the final state and measure an upper limit for the ratio of the branching fractions of the to and of at confidence level. The ratio of and coherent production cross sections is measured to be .
- Received 4 December 2009
DOI:https://doi.org/10.1103/PhysRevC.81.044901
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