Rho0 Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR [electronic resource].

Published: Berkeley, Calif. : Lawrence Berkeley National Laboratory. Nuclear Science Division, 2007.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Additional Creators: Lawrence Berkeley National Laboratory, Lawrence Berkeley National Laboratory. Nuclear Science Division, and United States. Department of Energy. Office of Scientific and Technical Information

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Summary

Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of ρ° and direct π⁺π⁻ photoproduction in ultra-peripheral relativistic heavy ion collisions at √s{sub NN} = 200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of σ(AuAu → Au*Au* ρ°) = 530 ± 19 (stat.) ± 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The ρ° transverse momentum spectrum (p{sub T}²) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus; we find σ{sub inc}/σ{sub coh} = 0.29 ± 0.03 (stat.) ± 0.08 (syst.). The ratio of direct π⁺π⁻ production is comparable to that observed in γp collisions at HERA, and appears to be independent of photon energy. Finally, the measured ρ° spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.

Report Numbers

E 1.99:lbnl-2101e
lbnl-2101e

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Note

Published through SciTech Connect.
12/20/2007.
"lbnl-2101e"
Physical Review C FT
STAR Coll.

Funding Information

DE-AC02-05CH11231

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