Photon 2003 Falk Meissner, LBNL Falk Meissner Lawrence Berkeley National Laboratory For the STAR Collaboration Photon 2003 April 2003 Coherent Electromagnetic Interactions in Coherent Electromagnetic Interactions in Ultra-Peripheral Heavy Ion Collisions Ultra-Peripheral Heavy Ion Collisions •Ultra Peripheral Collisions •Exclusive Meson Production •Data Sets and Analysis •Cross Sections •Photon-Photon Interactions •Summary
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Photon 2003Falk Meissner, LBNL Falk Meissner Lawrence Berkeley National Laboratory For the STAR Collaboration Photon 2003 April 2003 Coherent Electromagnetic.
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Photon 2003 Falk Meissner, LBNL
Falk Meissner Lawrence Berkeley National Laboratory
For the STAR Collaboration
Photon 2003 April 2003
Coherent Electromagnetic Interactions in Coherent Electromagnetic Interactions in Ultra-Peripheral Heavy Ion CollisionsUltra-Peripheral Heavy Ion Collisions
•Ultra Peripheral Collisions•Exclusive Meson Production•Data Sets and Analysis•Cross Sections•Photon-Photon Interactions•Summary
Physics Topics:Validity of WWA and factorizationStrong field QED Z ~ 0.6Large cross section Z44
Au
Au
e-
e+
200GeV, 0.25T Magnetic Field
Acceptance corrected pair pT
Coherent e+e- Pairs
pT < h/b ~20MeV (<b>~40fm)
Identified e+e - via dE/dx only at low momentum p<0.13 GeV
Small acceptance (~10-6) for e+e- pairs
cross section is peaked in the forward region and at low (non-reconstruct able) invariant mass
Manetic field cuts of very low momentum tracks (<60MeV) where cross section is large
Photon 2003 Falk Meissner, LBNL
* Normalized to total hadronic cross-section,
10% systematic error
Cross-sectionCross-section
Within acceptance0.14<Mee<0.26 GeV, ||<1.15
Total 4 cross section 33kB!
1-mbarn 62L
mb8.7
18%17% mb0.6
predicted
measured
STAR PRELIMINARY
Predictions LO QEDS.Klein V.Morozov
W
dWd ee /
Phd. Thesis V. Morozov
Photon 2003 Falk Meissner, LBNL
SummarySummary• First measurements for coherent meson production in ultra-peripheral First measurements for coherent meson production in ultra-peripheral
heavy ion collisions with and without nuclear excitation heavy ion collisions with and without nuclear 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• Cross section for electron-pair production reproduced by LO calculations• This is just the beginning; Future analysis topics:
– Vector meson spectroscopy ,excited states (*,…)– Multiple VM production– Hard diffraction - higher mass states J/– 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.