Observation of Two-source Interference in the Photoproduction Reaction Au Au ---> Au Au rho0

The collaboration
Phys.Rev.Lett. 102 (2009) 112301, 2009.

Abstract (data 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(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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Data from Figure 1 right bottom

10.17182/hepdata.98964.v1/t1

Rapidity (left) and $M_{\pi\pi}$ (right) of the $\pi^{+}\pi^{-}$ distributions for the topology (exclusive $\rho^0$, top) and MB (Coulomb breakup, bottom)...

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Data from Figure 1 right top

10.17182/hepdata.98964.v1/t2

Rapidity (left) and $M_{\pi\pi}$ (right) of the $\pi^{+}\pi^{-}$ distributions for the topology (exclusive $\rho^0$, top) and MB (Coulomb breakup, bottom)...

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Data from Figure 2

10.17182/hepdata.98964.v1/t3

Raw (uncorrected) ρ0 $t_{\perp}$-spectrum in the range 0.0 < |y| < 0.5 for the MB data. The points are data,...

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Data from Figure 3 left top

10.17182/hepdata.98964.v1/t4

Efficiency corrected $t_{\perp}$ spectrum for $\rho^{0}$ from (top) minium bias and (bottom) topology data, for mid-rapidity (left) and larger rapidity...

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Data from Figure 3 right top

10.17182/hepdata.98964.v1/t5

Efficiency corrected $t_{\perp}$ spectrum for $\rho^{0}$ from (top) minium bias and (bottom) topology data, for mid-rapidity (left) and larger rapidity...

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Data from Figure 3 left bottom

10.17182/hepdata.98964.v1/t6

Efficiency corrected $t_{\perp}$ spectrum for $\rho^{0}$ from (top) minium bias and (bottom) topology data, for mid-rapidity (left) and larger rapidity...

• #### Figure 3 right bottom

Data from Figure 3 right bottom

10.17182/hepdata.98964.v1/t7

Efficiency corrected $t_{\perp}$ spectrum for $\rho^{0}$ from (top) minium bias and (bottom) topology data, for mid-rapidity (left) and larger rapidity...