Journal
PHYSICAL REVIEW C
Volume 96, Issue 5, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevC.96.054904
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Funding
- RHIC Operations Group
- RCF at BNL
- NERSC Center at LBNL
- Open Science Grid consortium
- Office of Nuclear Physics within U.S. DOE Office of Science
- U.S. National Science Foundation
- Ministry of Education and Science of the Russian Federation
- National Natural Science Foundation of China
- Chinese Academy of Science
- Ministry of Science and Technology of China
- Chinese Ministry of Education
- National Research Foundation of Korea
- GA and MSMT of the Czech Republic
- Department of Atomic Energy of the Government of India
- Department of Science and Technology of the Government of India
- National Science Centre of Poland
- National Research Foundation of Croatia
- Ministry of Science, Education and Sports of the Republic of Croatia
- RosAtom of Russia
- German Bundesministerium fur Bildung, Wissenschaft, Forschung and Technologie (BMBF)
- Helmholtz Association
- Direct For Mathematical & Physical Scien
- Division Of Physics [1613939] Funding Source: National Science Foundation
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The STAR Collaboration reports on the photoproduction of pi(+) pi(-) pairs in gold-gold collisions at a center-of-mass energy of 200 GeV/nucleon-pair. These pion pairs are produced when a nearly real photon emitted by one ion scatters from the other ion. We fit the pi(+) pi(-) invariant-mass spectrum with a combination of rho(0) and omega resonances and a direct pi(+) pi(-) continuum. This is the first observation of the omega in ultraperipheral collisions, and the first measurement of rho-omega interference at energies where photoproduction is dominated by Pomeron exchange. The omega amplitude is consistent with the measured gamma p -> omega p cross section, a classical Glauber calculation, and the omega -> pi(+) pi(-) branching ratio. The omega phase angle is similar to that observed at much lower energies, showing that the rho-omega phase difference does not depend significantly on photon energy. The rho(0) differential cross section d sigma/dt exhibits a clear diffraction pattern, compatible with scattering from a gold nucleus, with two minima visible. The positions of the diffractive minima agree better with the predictions of a quantum Glauber calculation that does not include nuclear shadowing than with a calculation that does include shadowing.
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