Coherent diffractive photoproduction of ρ<SUP>0</SUP> mesons on gold nuclei at 200 GeV/nucleon-pair at the Relativistic Heavy Ion Collider



Adamczyk, L, Adkins, JK, Agakishiev, G, Aggarwal, MM, Ahammed, Z, Ajitanand, NN, Alekseev, I, Anderson, DM, Aoyama, R, Aparin, A
et al (show 339 more authors) (2017) Coherent diffractive photoproduction of ρ<SUP>0</SUP> mesons on gold nuclei at 200 GeV/nucleon-pair at the Relativistic Heavy Ion Collider. PHYSICAL REVIEW C, 96 (5). 054904-.

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Abstract

The STAR Collaboration reports on the photoproduction of π+π- 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 π+π- invariant-mass spectrum with a combination of ρ0 and ω resonances and a direct π+π- continuum. This is the first observation of the ω in ultraperipheral collisions, and the first measurement of ρ-ω interference at energies where photoproduction is dominated by Pomeron exchange. The ω amplitude is consistent with the measured γp→ωp cross section, a classical Glauber calculation, and the ω→π+π- branching ratio. The ω phase angle is similar to that observed at much lower energies, showing that the ρ-ω phase difference does not depend significantly on photon energy. The ρ0 differential cross section dσ/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.

Item Type: Article
Uncontrolled Keywords: 5106 Nuclear and Plasma Physics, 5107 Particle and High Energy Physics, 5110 Synchrotrons and Accelerators, 51 Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 04 Feb 2020 16:26
Last Modified: 22 Jun 2024 07:21
DOI: 10.1103/PhysRevC.96.054904
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3073453