1. Recoil Polarization Measurements in  0 Electroproduction at the Peak of the  (1232) By: Adam J. Sarty On behalf of the Hall A and E91-011 Collaborations NSTAR2001 Workshop on the Physics of Excited Nucleons University of Mainz March 7-10, 2001 A Status Report (and some Preliminary Results) From JLab E91-011 in Hall A

2. Acknowledgments: This Experiment (E91-011) ran in Hall A from May 19 – August 31, 2000. This talk is possible due to the contributions and hard work of many collaborators… The Other Co-Spokespeople: Jim Kelly (Maryland), Salvatore Frullani (INFN)Jim Kelly (Maryland), Salvatore Frullani (INFN) Robert Lourie (Rentec) – spokesperson EmeritusRobert Lourie (Rentec) – spokesperson Emeritus The Hardworking PhD Students: Rikki Roche’ (FSU)Rikki Roche’ (FSU) Zhengwhei Chai (MIT)Zhengwhei Chai (MIT) Stephanie Escoffier (Saclay)Stephanie Escoffier (Saclay) And Postdocs who led (leading!) the effort: Mark Jones (Maryland, now JLab)Mark Jones (Maryland, now JLab) Dave Meekins (FSU, now JLab)Dave Meekins (FSU, now JLab)

3. …and the rest of the Hall A Collaboration participants:

4. How can 1 more measurement in Hall A contribute to the “N-  ” problem? Given this is the 5 th N-  talk in a row, I’ll skip the “Motivation” discussion driving the interest to isolate S 1+ and M 1+ (and other!) contributions in e+p  e+p+  0 at W=1232! Focal Plane Polarimeter: (FPP) Tools in Hall A: 2 Hi-Res Specs (6 msr each) FPP High I, high Pol. cw beam 15 cm LH2 cryotarget E 0 up to 5 GeV Hall A

5. Measurement Philosophy: High-resolution recoil polarization measurements should be done at selected kinematic regions for stringent evaluation of multipole amplitudes.High-resolution recoil polarization measurements should be done at selected kinematic regions for stringent evaluation of multipole amplitudes. Access to unique multipole combinations and phase information not available with other methods.Access to unique multipole combinations and phase information not available with other methods. Complement the CLAS multipole extractions via a more extensive “energy independent” analysis.Complement the CLAS multipole extractions via a more extensive “energy independent” analysis. Warren, 98Schmeiden, 00Power of recoil-pol technique demonstrated with “single point” measurements from Bates ( Warren, 98 ) and Mainz ( Schmeiden, 00 ) (or: “why do we need this, given all that extensive Hall B data?”)

6. Our Choice of Q 2 compared to Existing Data for EMR & SMR:

7. Specific Measurements: p( e,e´p )  0 Angular Distribution of diff. Cross sections and Recoil Polarization in p( e,e´p )  0 Allows for multiple Response Function extraction. CENTRAL PRODUCTION KINEMATICS: (1 electron setting, 12 proton settings)

8. Accessible Response Functions:

9. Phase-Space Coverage Achieved “in-plane” part only allows extraction of distributions for 6 responses“in-plane” part only allows extraction of distributions for 6 responses Extended “out-of-plane” acceptance (from cm-lab boost) provides potential access to several more.Extended “out-of-plane” acceptance (from cm-lab boost) provides potential access to several more. Each response: unique combination of contributing multipolesEach response: unique combination of contributing multipoles Unique access to imaginary part of multipole interferences – phase info.Unique access to imaginary part of multipole interferences – phase info.  cm 

10. Evaluation of Expected Sensitivity to SMR: Above “sensitivity checks” done by using a simple isobar-model (JJ Kelly’s “eipiprod”), and allow SMR to vary away from VPI (SAID) database values. 4 graphs outlined in GREEN are the Responses accessible IN-PLANE.

11. Evaluation of Expected Sensitivity to EMR: Above “sensitivity checks” done same way as previous slide’s SMR checks. Basically NO SENSITIVITY to EMR.

12. Symmetries and Redundancies in Multipole Analysis

13. From The Experiment: Beam Polarization mid-high 70%’s Average current (whole run) = 45  A (143 Coulombs) Current: for mid-June to August Luminosity Monitoring: 108.2  A, P=79%

14. Sample Spectra #1: Background Subtraction

15. Sample Spectrum #2: Proton/Pion Separation

16. Sample Spectum #3: Separation from Elastic Radiative Tail  cm = -50° Radiative Tail from elastic peak only present in TWO of the 12 proton settings: for  cm = -50° and  cm = -90°

17. Sample Spectrum #4:

18. Sample Spectra #5: Data compared to MAID (input generator for acceptance Monte-Carlo routine) Data in RED MAID (+M.C.) in BLUE. Various spec. Distributions (y,  tgt,  tgt,  p) For both e and p Spectrometers. W Distribution  cm = 50°

19. FPP (Polarimeter) Performance Checks using H(e,e’p) Elastic Performed several dedicated elastic scattering runs with proton momenta spanning range of production settings Used to check/calibrate “false” (instrumental) asymmetries in FPP. Can also use Radiative Tail in acceptance of production kin.  cm = -90° to check same. False Asym. Distributions in FPP

20. FPP (Polarimeter) Performance Checks using H(e,e’p) Elastic #2: Extracting G E / G M Preliminary From rad.-tail Dedicated elastic run Comparison to (Black points) elastic measurement E93-027 made with same device: M.K. Jones et al, PRL 84, 1398 (2000)

21. Planned Analysis Method: Response Function fit to Focal Plane Polarizations

22. Monte-Carlo Evaluation of Planned Response-Function Extraction Method: Preliminary Simulation Study This is NOT data! Use M.C. (MAID input) to simulate expected focal plane pol. distributions. Extract Resp. Fn’s by directly fitting  distribution of focal-plane polarizations. Compare to input MAID calc’s…mostly OK, still needs a little study.

23. Monte-Carlo Evaluation of Planned Response-Function Extraction Method #2: Preliminary Simulation (NOT data!)

24. Preliminary (“On-Line”) Results: Sample #1

25. Preliminary (“On-Line”) Results: Sample #2

26. Preliminary (“On-Line”) Results: Sample #3

27. Summary:Summary: p( e,e´p )  0 has been measured for 12 angular settings, spanning the full range on either “side” of q.p( e,e´p )  0 has been measured for 12 angular settings, spanning the full range on either “side” of q. Measurements centered at pole of  (1232) excitation and at Q 2 = 1.0 GeV 2Measurements centered at pole of  (1232) excitation and at Q 2 = 1.0 GeV 2 Preliminary analysis shows there should be no problems extracting several response functions, including those beyond the 6 in- plane responses, due to large  acceptance.Preliminary analysis shows there should be no problems extracting several response functions, including those beyond the 6 in- plane responses, due to large  acceptance. “On-Line” polarizations show marked deviations from that expected (from MAID or SAID).“On-Line” polarizations show marked deviations from that expected (from MAID or SAID). Could be first hint at the sensitivity of this technique for accessing otherwise “hidden” multipole information.Could be first hint at the sensitivity of this technique for accessing otherwise “hidden” multipole information. Need to await completion of analysis to make firm statements / conclusions.Need to await completion of analysis to make firm statements / conclusions. Potential exists now to extend technique to other (higher) Q 2 and/or to off-peak W-values.Potential exists now to extend technique to other (higher) Q 2 and/or to off-peak W-values.

28. Focal-Plane Polarizations to Reaction-CM Polarizations

29. Very Preliminary Cross Section Results:

30. Spin Precession through HRS