The Proton Charge Radius Experiment (Rpex) has been conditionally approved by the Bates PAC (see their report).  The PAC requests the following for the full approval of the proposal:

• Complete a more detailed analysis of the experiment, including the required angular precision and the effects of the target holding field;
• Demonstrate operation of the SHR at 275 MeV with high current, high polarization beam, or present reasonable plans for moving the target upstream to permit operation at higher energy. 

Polarized electron beam at 275 MeV:

• Operating the storage ring at 275 MeV, which will be tested next year, possibly during the BLAST commissioning period.  If operating the machine at 275 MeV is not practical, the solution is to move the target upstream so that we can run at a slightly higher beam energy.  The target needs to be moved 15.65 cm upstream in order to run at 300 MeV.  The electron beam peak current higher than that required by this experiment was demonstrated recently by the polarized electron group at Bates.

• The atomic beam source (ABS): one possibility.  However, the H polarization from the ABS as high as 80% is needed.
• The laser-driven target: the other possibility.  This target has the potential to achieve better figure-of-merit than that of ABS. Currently, this target is being developed. 
• The holding field magnet design for the experiment and the magnetic field mapping.

• The singles measurement looks feasible from the preliminary analysis of the spring 2000 ring test run. More study is needed during the BLAST commissioning running.
• Coincidence measurement using the silicone strip recoil detectors for detector calibration.
• Detector calibrations for drift chambers, cerenkov detectors and scintillators.
• Target and detector collimators.

• Reconstruction in the presence of the target holding field for either ABS or LDT.
• Relative acceptance study.
• Q^2 determination, theta* determination.
• Complete simulation of the experiment.
• Data analysis.