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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
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Recoil Polarization Measurements in0 Electroproductionat 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
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) • Robert Lourie (Rentec) – spokesperson Emeritus • The Hardworking PhD Students: • Rikki Roche’ (FSU) • Zhengwhei Chai (MIT) • Stephanie Escoffier (Saclay) • And Postdocs who led (leading!) the effort: • Mark Jones (Maryland, now JLab) • Dave Meekins (FSU, now JLab) Acknowledgments:
Given this is the 5th N- talk in a row, I’ll skip the “Motivation” discussion driving the interest to isolate S1+ and M1+ (and other!) contributions in e+p e+p+0 at W=1232! How can 1 more measurement in Hall A contribute to the “N-” problem? Hall A 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 • E0 up to 5 GeV
Measurement Philosophy: (or: “why do we need this, given all that extensive Hall B data?”) • 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. • Complement the CLAS multipole extractions via a more extensive “energy independent” analysis. • Power of recoil-pol technique demonstrated with “single point” measurements from Bates (Warren, 98) and Mainz (Schmeiden, 00)
Angular Distribution of diff. Cross sections and Recoil Polarization in p( e,e´p )0 • Allows for multiple Response Function extraction. Specific Measurements: CENTRAL PRODUCTION KINEMATICS: (1 electron setting, 12 proton settings)
Phase-Space Coverage Achieved • “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. • Each response: unique combination of contributing multipoles • Unique access to imaginary part of multipole interferences – phase info. cm
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.
Evaluation of Expected Sensitivity to EMR: • Above “sensitivity checks” done same way as previous slide’s SMR checks. • Basically NO SENSITIVITY to EMR.
Beam Polarization mid-high 70%’s • Average current (whole run) = 45 A(143 Coulombs) From The Experiment: 108.2 A, P=79% Current:for mid-June to August Luminosity Monitoring:
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° andcm = -90°
Sample Spectra #5:Data compared to MAID (input generator for acceptance Monte-Carlo routine) cm = 50° W Distribution Various spec. Distributions (y, tgt , tgt, p) For both e and p Spectrometers. Data in RED MAID (+M.C.) in BLUE.
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. FPP (Polarimeter) Performance Checks using H(e,e’p) Elastic False Asym. Distributions in FPP
FPP (Polarimeter) Performance Checks using H(e,e’p) Elastic #2:Extracting GE / GM From rad.-tail Preliminary Dedicated elastic run • Comparison to (Black points) elastic measurement E93-027 made with same device:M.K. Jones et al, PRL 84, 1398 (2000)
Planned Analysis Method:Response Function fit to Focal Plane Polarizations
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.
Monte-Carlo Evaluation of Planned Response-Function Extraction Method #2: Preliminary Simulation (NOT data!)
Summary: • p( e,e´p )0has been measured for 12 angular settings, spanning the full range on either “side” of q. • Measurements centered at pole of (1232) excitation and at Q2 = 1.0 GeV2 • 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). • 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. • Potential exists now to extend technique to other (higher) Q2 and/or to off-peak W-values.
