学術雑誌論文 Coherent diffractive photoproduction of ρ0 mesons on gold nuclei at 200 GeV/nucleon-pair at the Relativistic Heavy Ion Collider

STAR Collaboration  ,  Esumi, S

96 ( 5 )  , p.054904 , 2017-11 , American Physical Society
ISSN:2469-9985
NII書誌ID(NCID):AA00773613
内容記述
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.
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