1. Precision Measurement of G E p /G M p with BLAST Chris Crawford MIT Laboratory for Nuclear Science for the BLAST collaboration

2. Motivation † Nucleon Electromagnetic Form Factors, Haiyan Gao, Int. J. of Mod. Phys. E, 12, No. 1, 1-40(Review) (2003)

3. Form Factor Ratio @ BATES  New technique: polarized beam and target  Exploits unique features of BLAST »internal target: low dilution, fast spin reversal »large acceptance: simultaneous measurement of all Q 2 points »symmetric detector: ratio measurement  Different systematics »insensitive to P b and P t  Q 2 = 0.07 – 0.9 (GeV/c) 2 »overlap with JLab data and RpEX (future exp. at Bates to measure r p )

4. Asymmetry Super-ratio Method  Polarized cross section  Super-ratio

5. Detector Package BLAST Coils Backward-Angle TOF TOF Scintillators Wire Chambers Cerenkov Detectors Neutron Detectors LADS Detectors

6. BLAST

7. Wire Chamber Tracking  Garfield drift time simulation  Newton-Rhapson track fitter  200μm resolution  20:1 signal to noise ratio

8. Preliminary Data Theta Resolution Beam Asymmetry Yield

9. Projected Results  Statistics »A 1, A 2  Systematics »θ * 1, θ * 2 Δp, Δθ, Δβ Errors are minimized as a function of β (target spin angle)

10. BLAST Collaboration 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