Interference Paper proposal
Interference in Vector Meson Production in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV
Paper proposal for PRL
S.Klein, B.Haag et al
Abstract
In ultra-peripheral 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 $\rho$ production is well localized at the two nuclei,
forming a 2-source interferometer. The two sources interfere, and
$\rho^0$ production at low transverse momentum is suppressed. The STAR collaboration
at RHIC reports measurements of this interference in 200 GeV per nucleon Au+Au collisions.
We observe interference at $93\pm 6\pm x\%$ of the expected level, and
find a maximum decoherence, due to wave function collapse or other
factors, of x\% at the 90\% confidence level.
Main Conclusions
- There is a clear suppression of the rho cross section at small t (pT2).
We see interference at the expected level.
- This shows that the post-rho-decay wave function must retain amplitudes for all
possible decays, long after the decay occurs. Since the &pi+ &pi- wave function
is spread out in space, this requires a non-local wave function.
Figures
Figure 1:
A schematic diagram of the two possibilities: a photon from nucleus 1 scattering from
nucleus 2, or vice versa.
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Figure 2:
The rapidity (top) and M&pi&pi (bottom)
distributions for the topology (exclusive &rho0 sample (left)
and minimum bias (Coulomb breakup) sample (right) ). The
points with error bars are the data, and the histograms
are the simulations.
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Figure 3:
Raw (uncorrected) t&perp spectrum for &rho0 sample
for 0.0 < |y|<0.5 for the minbias data. The points are the data,
while the diagonally hatched histogram is a simulation assuming that there is
interference; the overlapping filled histogram is a simulation without interference.
The dashed histogram is the wrong-sign background.
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