Interference in Coherent Vector Meson Production in UPC Au+Au Collisions at √s = 200GeV

1. Interference in Coherent Vector Meson Production in UPC Au+Au Collisions at √s = 200GeV Brooke Haag UC Davis STAR Collaboration Meeting, MIT, July 2006

2. Outline • Ultra Peripheral Heavy Ion Collisions (UPCs) • What is a UPC? • Vector Meson Production / Interference • STAR detectors / Triggers • Analysis of UPC events • Fitting Scheme • Observation of interference effects in t spectrum • Systematic Errors and Outlook STAR Collaboration Meeting, MIT, July 2006

3. Au Au Ultra Peripheral Collisions • What is a UPC? • Photonuclear interaction • Two nuclei “miss” each other (b > 2RA), electromagnetic interaction dominates over strong interaction • Photon flux ~ Z2 • Weizsacker-Williams Equivalent Photon Approximation • No hadronic interactions .. STAR Collaboration Meeting, MIT, July 2006

4. Exclusive ro Production Au+AuAu+Au+ro • Photon emitted by a nucleus fluctuates to virtual qq pair • Virtual qq pair elastically scatters from other nucleus • Real vector meson (i.e. J/, o) emerges • Photon and pomeron are emitted coherently • Coherence condition limits transverse momentum of produced  Courtesy of F. Meissner STAR Collaboration Meeting, MIT, July 2006

5. Au* Au g (2+g) r0 P Au Au* ro Production With Coulomb Excitation Au+AuAu*+Au*+ro • Coulomb Excitation • Photons exchanged between ions give rise to excitation and subsequent neutron emission • Process is independent of o production Courtesy of S. Klein STAR Collaboration Meeting, MIT, July 2006

6. Courtesy of S. Klein Interference Nucleus 2 emits photon which scatters from Nucleus 1 Nucleus 1 emits photon which scatters from Nucleus 2 -Or- • Amplitude for observing vector meson at a distant point is the convolution of two plane waves: • Cross section comes from square of amplitude: • We can simplify the expression if y  0: STAR Collaboration Meeting, MIT, July 2006

7. Time Projection Chamber Zero Degree Calorimeter Zero Degree Calorimeter Central Trigger Barrel STAR Analysis Detectors STAR Collaboration Meeting, MIT, July 2006

8. Triggers Au+AuAu+Au+ro UPC Topology • Central Trigger Barrel divided into four quadrants • Verification of r decay candidate with hits in North/South quadrants • Cosmic Ray Background vetoed in Top/Bottom quadrants Au+AuAu*+Au*+ro UPC Minbias • Minimum one neutron in each Zero Degree Calorimeter required • Low Multiplicity • Not Hadronic Minbias! Trigger Backgrounds • Cosmic Rays • Beam-Gas interactions • Peripheral hadronic interactions • Incoherent photonuclear interactions STAR Collaboration Meeting, MIT, July 2006

9. Studying the Interference • Determine  candidates by applying cuts to the data STAR Collaboration Meeting, MIT, July 2006

10. Studying the Interference • Generate similar MC histograms STAR Collaboration Meeting, MIT, July 2006

11. Studying the Interference • Generate MC ratio • Fit MC ratio STAR Collaboration Meeting, MIT, July 2006

12. C = 1.034±0.131 C = 0 Measuring the Interference • A= overall normalization • k = exponential slope • c = degree of interference • Apply overall fit c = 1 expected degree of interference c = 0 no interference C = 1.034±0.131 STAR Collaboration Meeting, MIT, July 2006

13. Results Minbias C = 1.009±0.081 2/DOF = 50.77/47 Topology C = 0.8487±0.1192 2/DOF = 87.92/47 Au+AuAu*+Au*+ro Au+Au Au+Au+ro STAR Collaboration Meeting, MIT, July 2006

14. Results Summary STAR Collaboration Meeting, MIT, July 2006

15. ~10% Interference routine for minbias 0 > y > 0.5 • flat ratio • statistics STAR Collaboration Meeting, MIT, July 2006

16. Systematic Error Study STAR Collaboration Meeting, MIT, July 2006

17. Systematic Error Study The 5 parameter fit is sufficient -- adding another parameter doesn’t improve the analysis. STAR Collaboration Meeting, MIT, July 2006

18. Paper Proposal http://www.star.bnl.gov/protected/pcoll/bhaag/NewPage/Frames.html STAR Collaboration Meeting, MIT, July 2006