A new proposal to the Jefferson Lab Program Advisory Committee (PAC34) Precision Measurement of the Neutron Magnetic Form Factor up to Q = 18.0 (GeV/c) by the Ratio Method

We propose to make a high-precision measurement of the neutron’s magnetic form factor, Gn M , at nine kinematic points: Q2 = 3.5, 4.5, 6.5, 8.5, 10., 12., 13.5, 16. and 18.0 (GeV/c)2. Little data on Gn M exists in this kinematic range and the existing data have large systematic uncertainties. In the proposed experiment, systematic errors are greatly reduced by the use of the “ratio” method in which Gn M is extracted from the ratio of neutron-coincident to proton-coincident quasi-elastic electron scattering from the deuteron. The experiment would be performed in Hall A using the BigBite spectrometer to detect the scattered electrons and the BigHAND to detect both neutrons and protons. A large aperture dipole magnet on the nucleon flight path will greatly enhance particle identification by slightly deflecting the protons. Calibration reactions will be used to produce tagged neutrons and protons at essentially the same momentum as the quasi-elastic nucleons. The efficiency of BigHAND is expected to be high and stable and to be well calibrated. Projected systematic errors on the measured ratio of cross sections vary from under 2% to 5% (1.% to 2.5% on the ratio of the magnetic form factor to that of the proton). Statistical errors are projected to be similar, or smaller. This proposal overlaps and significantly extends the kinematics range of the already approved 12 GeV CLAS proposal, E12-07-104, which predicts similar uncertainties up to 13.5 (GeV/c)2. The present proposal includes measurements at Q2 beyond the range of that experiment and will have significantly greater statistics for the highest-Q2 points covered by E12-07-104. We request a total of 48.5 days divided among four beam energies, 4.4, 6.6, 8.8 and 11. GeV.