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We present a measurement of pi^+pi^-pi^+pi^- photonuclear production inultra-peripheral Au-Au collisions at sqrt(s_{NN}) = 200 GeV from the STARexperiment. The pi^+pi^-pi^+pi^- final states are observed at low transversemomentum and are accompanied by mutual nuclear excitation of the beamparticles. The strong enhancement of the production cross section at lowtransverse momentum is consistent with coherent photoproduction. Thepi^+pi^-pi^+pi^- invariant mass spectrum of the coherent events exhibits abroad peak around 1540 pm 40 MeV/c^2 with a width of 570 pm 60 MeV/c^2, inagreement with the photoproduction data for the rho^0(1700). We do not observea corresponding peak in the pi^+pi^- final state and measure an upper limit forthe ratio of the branching fractions of the rho^0(1700) to pi^+pi^- andpi^+pi^-pi^+pi^- of 2.5 % at 90 % confidence level. The ratio of rho^0(1700)and rho^0(770) coherent production cross sections is measured to be 13.4 pm 0.8(stat.) pm 4.4 (syst.) %.

Observation of pi^+pi^-pi^+pi^- Photoproduction in Ultra-Peripheral Heavy Ion Collisions at sqrt{s_NN} = 200 GeV at the STAR Detector