Run Plan

Table 3 shows the proposed run plan for the experiment. We will take data in both spectrometers simultaneously for all kinematics. Data will be taken on 4cm LH₂ and aluminum 'dummy' targets for endcap subtraction. An arc energy measurement and e-p energy measurement will be done at each beam energy, and the spectrometer will be surveyed before (or after) each data taking run. The checkout runs will include sieve slit runs with electron singles and elastic coincidences, and sieve slit runs with a long (15cm) target and with the variable z-position optics target to measure any correlation between target position and reconstructed scattering angle.

In addition to the proton inclusive data for the G_E/G_M measurement, we will take several test measurements. Runs will be taken at different beam currents in order to verify our measurement of the dead time in the spectrometers. Data will be taken with a thin carbon target at all kinematics as a check on the spectrometer pointing. Finally, because we define the kinematics by the proton angle, we can use the measured proton momentum as a check on the kinematics. While for a single setting, it is not possible to disentangle a momentum offset from a scattering angle offset, the magnets settings stay the same when the scattering angle is changed, and so any momentum offset will be identical at all epsilon points for a given Q². The reproducibility of the magnet settings, important if one of the magnet trips and has to be reset, is $\sim$10^-4, small enough that it is not a significant problem for kinematics checks. This will allow us to use the reconstructed momentum as an additional check on the kinematics.

Finally, coincidence data will be taken at some energies as a check of the scattering kinematics, and as a measure of proton detection efficiency and absorption (though these corrections almost completely cancel in the extracted ratios). For Q²=1.45 GeV², we will take singles and coincidence data at coincidence kinematics at 1, 2, and 3 passes. Comparing the elastic cross section as measured by the protons and the electrons at one kinematics allows us to measure the proton inefficiency (due mainly to absorption). By comparing electron singles to proton singles at multiple kinematics (with a fixed proton momentum), we can also check the radiative corrections, which are significantly different for electron and proton singles.

 

 

Checkout, calibration, and sieve runs at 1.16 GeV. 20 hours

Singles and coincidence H₂ data at 3 beam currents. 3+1 hours 24 hours

Move spectrometers to coincidence Q² = 1.45 and survey. 6 hours

Coincidence run at Q² = 1.45. 2+1 hours

Move electron spectrometer to proton Q² = 0.5 and survey. 6 hours

Data run at Q² = 0.5 and 1.45. 1+1 hours

Change energy to 2.26 GeV and move spectrometers. 8 hours

Data run at Q² = 0.5 and 1.45. 2+1 hours

Survey spectrometers. 6 hours

Move spectrometers to coincidence Q² = 1.45 and survey. 6 hours

Coincidence run at Q² = 1.45 4+2 hours

Change energy to 5.56 GeV and move spectrometers. 8 hours

Data run at Q² = 0.5 and 1.45. 1+1 hours

Survey spectrometers. 6 hours 62 hours

Move spectrometers to Q² = 0.5 and 3.20 and survey. 6 hours

Data run at Q² = 0.5 and 3.20. 10+3 hours

Change energy to 2.26 GeV and move spectrometers. 8 hours

Data run at Q² = 0.5 and 3.20. 8+2 hours

Survey spectrometers. 6 hours

Change energy to 3.36 GeV and move spectrometers. 8 hours

Data run at Q² = 0.5 and 3.20. 12+3 hours

Survey spectrometers. 6 hours

Move spectrometers to coincidence Q² = 1.45 and survey. 6 hours

Coincidence run at Q² = 1.45. 4+2 hours 84 hours

Move spectrometers to Q² = 0.5 and 4.90 and survey. 6 hours

Data run at Q² = 0.5 and 4.90. 20+5 hours

Change energy to 5.56 GeV and move spectrometers. 8 hours

Data run at Q² = 0.5 and 4.90. 20+5 hours

Survey spectrometers. 6 hours 70 hours

Total 240 hours

  

Figure: $\mu_pG_E/G_M$ as deduced from polarization transfer [4] (closed diamonds) and a global analysis of L-T separation experiments [1] (open diamonds). The circles show the projected uncertainties for the proposed measurement for two different assumptions. The closed circles assume $\mu_pG_E$/G_M=1 and the open circles are based on a fit to the Hall A data (dashed line).