Precision Measurement of G E p /G M p with BLAST

1. Precision Measurement of GEp/GMp with BLAST Chris Crawford MIT Laboratory for Nuclear Science Ricardo Alarcon, John Calarco, Ben Clasie, Haiyan Gao, Hauke Kolster, Jason Seely, Tim Smith, Vitaliy Ziskin, and the BLAST Collaboration

2. Outline • Introduction and Motivation • Theoretical calculations • Existing Measurements • Rosenbluth technique • Recoil proton polarization (FPP) • Super Rosenbluth • BLAST Experiment • Asymmetry super-ratio method • Polarized beam, polarized targets, detectors • Projected Results

3. Introduction • GE,GM fundamental quantities describing charge/magnetization in the nucleon • Test of QCD based calculations and models • Provide basis for understanding more complex systems in terms of quarks and gluons

4. Kinematics Mott Cross Section Form Factor Dipole Form Factor Elastic Scattering

5. Rosenbluth Separation • Elastic e-p cross section • At fixed Q2, fit dσ/dΩ vs. tan2(θ/2) • Measurement of absolute cross section • Dominated by either GE or GM

6. Unpolarized World Data

7. Polarization Transfer • Recoil proton polarization • Focal Plane Polarimeter • recoil proton scatters off secondary 12C target • Pt, Pl measured fromφ distribution • Pb, and analyzing powercancel out in ratio

8. World Data • Unpolarized Data • Polarization Transfer • Milbrath et al. (BATES) 1999 • Jones et al. (JLAB), 2000 • Dieterich et al. (MAMI), 2001 • Gayou et al. (JLAB), 2002 • Super-Rosenbluth • JLab Hall A, preliminaryresults expected soon

9. Super Rosenbluth Separation

10. Theory† • Direct QCD calculations • pQCD scaling at high Q2 • Lattice QCD • Meson Degrees of Freedom • Vector Meson Dominance (VMD), Lomon 2002 • Dispersion analysis, Höhler et al. 1976 • VMD + Chiral Perturbation Theory, Mergel et al. 1996 • QCD based quark models • CQM, Frank et al. 1996 • Soliton Model, Holzwarth 1996 • Cloudy bag, Lu et al. 1998 †Nucleon Electromagnetic Form Factors, Haiyan Gao, Int. J. of Mod. Phys. E, 12, No. 1, 1-40(Review) (2003)

11. Perturbative QCD diverges at low Q2 F2/F1 scaling Lattice QCD must extrapolate tophysical pion mass quenched calculations QCD Calculations

12. Vector Meson Dominance Dispersion Analysis Meson Based Models

13. Relativistic CQM Soliton Model Cloudy Bag Model Models in closest agreement with recent JLab results: Constituent Quark Models

14. Form Factor Ratio @ BATES • New technique: polarized beam and target • exploits unique features of BLAST • different systematics • insensitive to Pb and Pt • Q2 = 0.07 – 0.9 (GeV/c) 2 • overlap with JLab dataand RpEX (future exp.at Bates to measure rp)

15. Asymmetry Super-ratio Method • Polarized cross section • Super-ratio

16. W.H. Bates Accelerator Facility

17. R. Alarcon, E. Geis, J. Prince, B. Tonguc, A. Young Arizona State University  J. Althouse, C. D’Andrea, A. Goodhue, J. Pavel, T. Smith, Dartmouth College T. Akdogan, W. Bertozzi, T. Botto, M. Chtangeev, B. Clasie, C. Crawford, A. Degrush, K. Dow, M. Farkhondeh, W. Franklin, S. Gilad, D. Hasell, E. Ilhoff, J. Kelsey, H. Kolster, A. Maschinot, J. Matthews, N. Meitanis, R. Milner, R. Redwine, J. Seely, S.Sobczynski, C. Tschalaer, E. Tsentalovich, W. Turchinetz, Y. Xiao, H. Xiang, C. Zhang, V. Ziskin, T. Zwart Massachusetts Institute of Technology Bates Linear Accelerator Center D. Dutta, H. Gao, W. Xu Duke University J. Calarco, W. Hersman, M. Holtrop, O. Filoti, P. Karpius, A. Sindile, T. Lee University of New Hampshire J. Rapaport Ohio University K. McIlhany, A. Mosser United States Naval Academy  J. F. J. van den Brand, H. J. Bulten, H. R. Poolman Vrije Universitaet and NIKHEF W. Haeberli, T. Wise University of Wisconsin BLAST Collaboration

18. Polarized Beam and Target • Stored electron beam (80 mA) Eb: 0.27–1.1 GeV Pb: 0.70 • 1H / 2D target (ABS)L: 1.0×1032/cm2 s Pt: 0.50 • 3He targetL: 1.2×1033/cm2 s Pt: 0.50

19. Polarization about 0.70 typical Statistical precision of measurements governed mostly by signal-to-background ratio. Typical precision of 1-2% per hour. Systematic errors estimated at 5% level presently. Working on reducing these through improved analysis of energy spectrum. Full photon energy spectrum measured as function of laser helicity and for background Polarization measurements made at currents up to 130 mA. Signal to background ratio worsens at high currents but still tractable. Compton Polarimeter

20. 1 1 1 1 MFT (2->3) 3 3 2 2 nozzle 4 6-pole 6-pole Atomic Beam Source • Standard technology • Dissociator & nozzle • 2 sextupole systems • 3 RF transitions Spin State Selection:

21. ABS Layout

22. ABS Specifications • Cell geometry: cylindrical 15mm × 400mm • Cell coating: Drifilm • Cell temperature: T=80K • Target thickness: t=4.4×1013 cm-2 (H) • Polarization: Pz = 0.59 (H), 0.78 (D) • Holding field: B=3mT (H), 35mT (D)

23. Ion polarimeter Ions produced by electron beam inside the storage cell are extracted and accelerated by electrostatic lenses. The spherical deflector directs ions into the polarimeter arm. The Wien Filter provides mass separation, and nuclear reaction with large analyzing power is used to measure nuclear polarization. Currently, the tritium target is not installed yet, and Ion Polarimeter is used as a mass spectrometer.

24. Laser Driven Source (LDS) • Optical pumping& Spin Exchange • Spincell design • Target and Polarimeter • Results

25. Spin-Exchange Optical pumping

26. LDS Experimental Setup

27. LDS Performance • Current Status • Flux: 1.1×1018 atoms/s • Atomic fraction: 0.56 • Polarization: 0.37 • Improvements • Diamond coating instead of drifilm • Double dissociator • Electro-Optic Modulator (EOM)

28. Detector Package • BLAST Torroid • TOF Scintillators • Čerenkov Detectors • Wire Chambers • Neutron Bars, LADS • Software

29. definition of the momentum transfer vector optimize statistics polarized targets: Atomic Beam & Laser Driven Sources simultaneous A-measurements e/p/n/ separation Detector Requirements ()e  2 , e   mrad, z  1 cm Large , beam current, luminosity, polarization Coil shape  1 m diameter in target region BLAST field = 0 at target B-gradients  50 mG/cm Symmetric Detector PID

30. BLAST Toroid

31. Detector Subframe

32. TOF Scintillators • timing resolution: σ=245 ps • ADC spectrum • coplanarity cuts

33. 1 cm thick aerogel tiles Refractive index 1.02-1.03 White reflective paint 80-90 % efficiency 5" PMT's, sensitive to 0.5 Gauss Initial problems with B field Required additional shielding 50% efficiency without shielding Čerenkov Detectors

34. Wire Chambers • 2 sectors × 3 chambers • 954 sense wires • resolution 200μ • signal to noise 20:1

35. Software • BLASTmc – Monte Carlo using Geant321 • BlastLib2 – recon library based on ROOT • integrated on-line display • and offline reconstruction • CODA – data acquisition • EPICS – slow controls

36. Scintillators timing, calibration Wire chamber hits, stubs, segments link, track fit PID, DST Reconstruction Steps

37. Tracking Resolution

38. Radiative Corrections • MASCARAD code • A. Afanasev et al., Phys.Rev.D 64,113009 • Covariant calculation with no cutoff parameter • small corrections (<1%) to asymmetry

39. Cross Section

40. Projected Results • Statistics • A1, A2 • Systematics • θ*1, θ*2 Δp, Δθ, Δβ Errors are minimized as a function of β (target spin angle)

41. Conclusion • The super-ratio method exploits unique characteristics of the BLAST detector • This is the first measurement of μGEp/GMp with polarized beam and target • An important complement to JLab data at higher Q2 values • If in doubt, take a RATIO…