1. Quark Matter 2002Falk Meissner, LBNL Falk Meissner Lawrence Berkeley National Laboratory For the STAR Collaboration Quark Matter 2002 19.07.02 Coherent Vector Meson Production in Ultra-Peripheral Heavy Ion Collisions Ultra Peripheral Collisions Exclusive Meson Production 2000/2001 Data Sets and Analysis Cross Sections Photon-Photon Interactions Summary

2. Quark Matter 2002Falk Meissner, LBNL Ultra-Peripheral Collisions Au X  P Nuclei ‘miss’ geometrically and interact via long range fields Coupling strength Coupling strength  large cross sections Photon-   Z 2 Equivalent Photon Approximation (Weizsaecker-Williams, Fermi) Pomeron- P  A 4/3 (surface) to A 2 (volume) Coherent coupling to extended charge of both nuclei    P > R_A  Small transverse momentum: p T < h/2R A ~ 90 MeV Longitudinal component P L <  h/2R A ~ 6 GeV Quasi Real Photons

3. 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 C60 014903 (1999), A. Baltz, S. Klein,J. Nystrand PRL 89, 012301 (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

4. Quark Matter 2002Falk Meissner, LBNL Experimental Signature of UPC Two oppositely charged tracks with vertex Low total p T Back-to-back in transverse plane ZDC CTB-Topology Challenge: Trigger ! Topology requirements in central trigger barrel (CTB) Coincident signals from nucl. Breakup in zero degree calorimeters (ZDC)

5. Quark Matter 2002Falk Meissner, LBNL Transverse Momentum & Invariant Mass Spectra 2000: 130 GeV; 9hrs dedicated, 30k triggers 2001: 200 GeV; trigger mix 1.5M topology triggers Peak at low p T  coherent interaction Background model from like-sign pairs normalized to data No neutron signal in ZDC  gold nuclei remain in ground state Signal region: p T <0.15 GeV Topology Trigger AuAu  AuAu  0 200GeV Preliminary

6. Quark Matter 2002Falk Meissner, LBNL Meson Production with Nuclear Break-up Minimum Bias (ZDC) Trigger AuAu  Au*Au*  0 ZDC Response Signal region: p T <0.15 GeV 2000: ~400k triggers L~60/mb 2001: ~1.7M triggers L~250/mb 200GeV Preliminary

7. Quark Matter 2002Falk Meissner, LBNL  Mass Fit Acceptance corrected Breit-Wigner+direct pion pair production+ BG Background contribution at low mass from e + e - pairs Amplitude ratio  similar to lepton nucleon scattering 130 GeV --  ++ A+-AA+-A

8. Quark Matter 2002Falk Meissner, LBNL Cross Section  (AuAu  Au (*) Au (*)  ) 130 GeV - nucl-ex/0206004, 200 GeV Preliminary Luminosity normalization from 7.2b hadronic AuAu cross section Systematic uncertainties ~20% Theory: A. Baltz, S. Klein J. Nystrand Preliminary Total No Breakup xn,xn 1n,1n

9. Quark Matter 2002Falk Meissner, LBNL Compare to lepton- nucleon scattering A dependence of photo-nuclear cross section VM Production mechanism depends on scale - c.m.s. energy, p T, quark masses J/  sensitive to gluon distribution in the nucleus A-Scaling and Energy Dependence

10. Quark Matter 2002Falk Meissner, LBNL Two-Photon Interaction Two-Photon Interaction AuAu  Au*Au*e + e - Identified e+e - Pairs via dE/dx only at low momentum p<0.13 GeV Non-Identified coherent e + e - pairs - background for  production; extrapolate identified e+e- to all momenta with MC Coherent e + e - Pairs p T ~40fm) Physics Topics:  Strong field QED Z  ~ 0.6  Large cross section  Z 4  4 Au   e-e- e+e+ 200GeV, 0.25T Magnetic Field

11. Quark Matter 2002Falk Meissner, LBNL Summary First measurements for coherent meson production in ultra-peripheral heavy ion collisions with and without nuclear excitation Au + Au -> Au + Au +   and Au + Au -> Au * + Au * +  . low p T = 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.

12. Quark Matter 2002Falk Meissner, LBNL

13. Quark Matter 2002Falk Meissner, LBNL Rapidity Extrapolation Y-distribution differs for  prod. with (xnxn,1n1n) and without (0n0n) breakup Nucl.Breakup STAR Data Acceptance is flat in p T and Mass Analysis |y|<1 Extrapolate to 4pi with MC

14. Quark Matter 2002Falk Meissner, LBNL Compilation of VM cross Sections

15. Quark Matter 2002Falk Meissner, LBNL Entangled 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 interference OR 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+ e-e- b J/  ++ 00 ???

16. Quark Matter 2002Falk Meissner, LBNL 2-slit interferometer with separation of impact paramter b! ~ 40 fermi >>R A ~ 7 fm  J  have negative parity J PC = 1 - - Amplitudes have opposite signs  ~ |A 1 - A 2 e ip·b | 2 destructive interference at p T =0 (maximal at y=0 when A 1 =A 2 ) Can’t differentiate between projectile and target Expected Signal No Interference Interference Interference S. Klein and J. Nystrand, Phys. Rev. Lett. 84(2000)2330