Status of Beam Asymmetry Measurements for Non-Strange Meson Photoproduction from g8b

1. Status of Beam Asymmetry Measurements for Non-Strange Meson Photoproduction from g8b ASU Meson Physics Group* (and friends) • Work at ASU is supported by the National Science Foundation Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

2. Spin observables • Differential cross sections are (relatively) simple • Spin observables access interferences I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B95, 347 (1975) Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

3. g8b running period(June 20- Sept 1, 2005) • Incident electron Ee= 4.55 GeV • 50-m diamond bremsstrahlung radiator • Linearly polarized photon beam (┴ , ║) • Coherent edge set at 1.3, 1.5, … 2.1 GeV → Eg= 1.1 to 2.1 GeV • 40-cm-long LH2 target • Trigger: single charged particle + tagger Oriented / Un-oriented Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

4. Photon beam polarization P Oriented/Un-oriented • Analytical QED coherent bremsstrahlung calculation fit to actual spectrum (Livingston/Glasgow)  • Unstable coherent edge location  • Determined regions of reliable photon beam polarization P • Estimated systematic uncertainty in P: ~3% Polarization Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

5. “Para/Perp” approach for extracting S • Use missing mass for reaction g + p → p + X • Construct kinematical bins for parallel, perpendicular, and unpolarized data subsets • Slice each kinematical bin into azimuthal angle φ slices (10, 20, 30 or so): “φ slice method” • Determine photoproduced meson yield in each slice • Fit φ dependence to A(1 + B cos(2φ)), whereB = SP . • Preliminary results shown are from Patrick Collins and Mike Dugger Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

6. Example: g p → p + n Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

7. Extracting S for g p → p + n High yield and/or high asymmetry is easy  Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

8. A much harder job: g p →η´ p Low yield and/or low asymmetry is tough  Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

9. Fourier moment method(CLAS Note 2008-35) • Simultaneously uses full azimuthal φacceptance of data set.  • Only a few (in principle, only 2) histograms per kinematic bin need to be fit. • Re-binning data is comparatively easier than with the φslice method. Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

10. Flux-normalized yields • Define a function f i,j for each kinematic bin i,j These are related to the yields normalized to integrated flux: Subscript denotes polarization: a↔ unpolarized ┴ ↔ perpendicular || ↔ parallel Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

11. Moments of flux-normalized yields • Expand the f i, j in Fourier series. For example, Find the nth moment for thef i,j(called Hn ): orthogonality Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

12. Solving these for S • Putting the pieces together, for the i,j kinematic bin, we find: • The Hn histograms are created by weighting each event bycos(nφ)for eachi,j kinematic bin. Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

13. Example: γ p → π0 p numerator denominator Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

14. Preliminary results for S from g8b • Preliminary results: p 0, p +, and h for 1.3 GeV coherent edge setting • Fourier moment method • Results from Mike Dugger’s work • “First and worst” coherent edge setting • Uncertainties in S less than 5% (more often ~1%) • Two ways to view preliminary results • Fixed energy (~9-MeV-wide photon energy bins) • Fixed angle (0.1-wide bins in cos q) • Both ways: compare with SAID predictions Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

15. Preliminary S results for p0 Fixed energy – 4 slides Fixed angle – 3 slide Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

16. Preliminary S results for p0 Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

17. Preliminary S results for p0 Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

18. Preliminary S results for p0 Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

19. Preliminary S results for p0 Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

20. Preliminary S results for p0 Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

21. Preliminary S results for p0 Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

22. Preliminary S results for p0 Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

23. Preliminary S results for p+ Fixed energy – 4 slides Fixed angle – 3 slides Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

24. Preliminary S results for p+ Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

25. Preliminary S results for p+ Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

26. Preliminary S results for p+ Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

27. Preliminary S results for p+ Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

28. Preliminary S results for p+ Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

29. Preliminary S results for p+ Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

30. Preliminary S results for p+ Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

31. Preliminary S results for h Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

32. Acceptance problem in g8b • Clump of dead/bad TOF counters give “divot” in γ p → h p missing mass • Simple background fit is problematic • Monte Carlo backgrounds should work (next step) Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

33. Choose a branch: h → p p +p -p 0 (G~22.7%) • Look at g p → p X • Look at MY for p X → p p +p -Y • Cut on MY=p 0 mass • Much less background under peak  • Lower acceptance (~ [0.5]2G  0.05)  Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

34. Using branch for h in g8b • Apply Fourier moment method for quick preliminary look. • Even with branch, lots of events in g8b • Ultimately will go back to proton yield in γ p → h p with good background MC Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

35. Preliminary S results for h 4 E-counters / bin Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

36. Preliminary S results for h 2 E-counters / bin Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

37. Preliminary S results for h 2 E-counters / bin Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

38. Summary • Good progress for the first/worst 200 MeV of photon energy range • Finish line is in sight for S for p + , p 0 , and h • Getting S for h′ will be tough but doable • The preliminary results for p + , p 0 , and h … • Look very good, even with fine binning • Incredibly stringent test for nucleon models • No indication of any narrow-width structures in any channel • Goal: All four mesons ready for review by end of year Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009

39. Meson Physics Group Patrick Collins Mike Dugger Brian Morrison Eugene Pasyuk Barry Ritchie Work at ASU is supported by the National Science Foundation Status of Beam Asymmetry Measurements for Meson Photoproduction ASU Meson Physics Group Hadron Spectroscopy WG Meeting – June 2009