Quark Matter 2002 Falk Meissner, LBNL Falk Meissner Lawrence Berkeley National Laboratory For the STAR Collaboration Quark Matter 2002 19.07.02 Coherent Vector Meson Production in Coherent Vector Meson Production in Ultra-Peripheral Heavy Ion Collisions Ultra-Peripheral Heavy Ion Collisions •Ultra Peripheral Collisions •Exclusive Meson Production •2000/2001 Data Sets and Analysis •Cross Sections •Photon-Photon Interactions •Summary
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Quark Matter 2002Falk Meissner, LBNL Falk Meissner Lawrence Berkeley National Laboratory For the STAR Collaboration Quark Matter 2002 19.07.02 Coherent.
Quark Matter 2002Falk Meissner, LBNL Exclusive Vector Meson Production A ’ VA Extrapolate p ’ Vp to A ’ VA with Glauber calculation Large cross sections: 350 mb at s NN 1/2 =130 GeV 590 mb at s NN 1/2 =200 GeV S.Klein, J.Nystrand, Phys. Rev C (1999), A. Baltz, S. Klein,J. Nystrand PRL 89, (2002) Factorize as function of impact parameter Nuclear breakup by single (1n1n) and multiple (xnxn )neutron emission single/multiple neutron emission selects different impact parameters Exclusive production AuAu AuAu 0 … with nuclear excitation AuAu Au*Au* 0
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Quark Matter 2002 Falk Meissner, LBNL
Falk Meissner Lawrence Berkeley National Laboratory
For the STAR Collaboration
Quark Matter 2002 19.07.02
Coherent Vector Meson Production in Coherent Vector Meson Production in Ultra-Peripheral Heavy Ion CollisionsUltra-Peripheral Heavy Ion Collisions
•Ultra Peripheral Collisions•Exclusive Meson Production•2000/2001 Data Sets and Analysis•Cross Sections•Photon-Photon Interactions•Summary
Identified e+e - Pairs via dE/dx only at low momentum p<0.13 GeVNon-Identified coherent e+e- pairs - background for production; extrapolate identified e+e- to all momenta with MC
Coherent e+e- Pairs pT < h/b (<b>~40fm)
Physics Topics:Strong field QED Z ~ 0.6Large cross section Z44
Au
Au
e-
e+
200GeV, 0.25T Magnetic Field
Quark Matter 2002 Falk Meissner, LBNL
SummarySummaryFirst measurements for coherent meson production in ultra-First measurements for coherent meson production in ultra-
peripheral heavy ion collisions with and without nuclear peripheral heavy ion collisions with and without nuclear excitation excitation
Au + Au -> Au + Au + and Au + Au -> Au* + Au* + .• low pT= coherent coupling• Cross Sections agree with predictions =>Approximate factorization of rho-production and nuclear excitation =>Weizsaecker-Williams photon flux from large relativistic charges ok. => Glauber extrapolation of N to Au ok• This is just the beginning; Future analysis topics:
– Vector meson spectroscopy ,excited states (*,…)– Multiple VM production– Hard diffraction - higher mass states J/– Strong field QED - e+e- pairs– Interference of decaying particles
RHIC is a good place to study diffractive and electromagnetic processes in heavy ion collisions. Lots of data and physics topics.
Quark Matter 2002 Falk Meissner, LBNL
Quark Matter 2002 Falk Meissner, LBNL
RapidityRapidityExtrapolationExtrapolation
• Y-distribution differs for prod. with (xnxn,1n1n) and without
(0n0n) breakup
Nucl.Breakup
STAR Data•Acceptance is flat in pT and Mass•Analysis |y|<1•Extrapolate to 4pi with MC
Quark Matter 2002 Falk Meissner, LBNL
Compilation of VM cross Sections Compilation of VM cross Sections
Quark Matter 2002 Falk Meissner, LBNL
Entangled Nonlocal WavefunctionsEntangled Nonlocal Wavefunctions• VM are short lived (~10-23 s) decay before traveling distance b• Decay products interfere
• J/s many decays: e+ e-, +- +- , hadrons• At the decay time(s) neither amplitude can know
about the other (no overlap)Either independent decays --> little/no interferenceOR The wave function retains amplitudes for all possible
decays, long after the decay occurs The wave function only collapses when it interacts
with the detector Quantum mechanics predicts choice 2 Example of the Einstein-Podolsky-Rosen paradox
+
-
+
-
b
-
e+
e-
b
J/
J/
+0
???
Quark Matter 2002 Falk Meissner, LBNL
2-slit interferometer with separation of impact paramter b!