# Observation of Two-source Interference in the Photoproduction Reaction $Au Au \to Au Au \rho^0$

Abstract : In ultra-peripheral relativistic heavy-ion collisions, a photon from the electromagnetic field of one nucleus can fluctuate to a quark-antiquark pair and scatter from the other nucleus, emerging as a $\rho^0$. The $\rho^0$ production occurs in two well-separated (median impact parameters of 20 and 40 fermi for the cases considered here) nuclei, so the system forms a 2-source interferometer. At low transverse momenta, the two amplitudes interfere destructively, suppressing $\rho^0$ production. Since the $\rho^0$ decay before the production amplitudes from the two sources can overlap, the two-pion system can only be described with an entangled non-local wave function, and is thus an example of the Einstein-Podolsky-Rosen paradox. We observe this suppression in 200 GeV per nucleon-pair gold-gold collisions. The interference is $87% \pm 5% {\rm (stat.)}\pm 8%$ (syst.) of the expected level. This translates into a limit on decoherence due to wave function collapse or other factors, of 23% at the 90% confidence level.
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Journal articles
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http://hal.in2p3.fr/in2p3-00349932
Contributor : Dominique Girod <>
Submitted on : Monday, January 5, 2009 - 2:06:50 PM
Last modification on : Thursday, August 6, 2020 - 6:23:56 PM

### Citation

B.I. Abelev, M.M. Aggarwal, Z. Ahammed, B.D. Anderson, D. Arkhipkin, et al.. Observation of Two-source Interference in the Photoproduction Reaction $Au Au \to Au Au \rho^0$. Physical Review Letters, American Physical Society, 2009, 102, pp.112301-7. ⟨10.1103/PhysRevLett.102.112301⟩. ⟨in2p3-00349932⟩

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