Abstract for JLAB Technical Note 02-032  

In conjunction with Hall A experiment E91-011 (N --> Delta) two sets (referred to here as Set II and Set III) each of five elastic 1H(e,e'p) kinematics were measured during the period May 20-21 and July 8-9, 2000 to determine the absolute angular offsets for each spectrometer. This is a follow-up of a previous scan during the period April 1-2, 2000 (Set I) in order to check whether the spectrometer absolute angular offsets are stable over time. The measurements were taken at two different beam energies of 4530:6+/-0:9 MeV (for Set II) and 3413:5 MeV (for Set III). For Set II this energy was derived from a measurement using the Hall A Arc system. For Set III, which used a 3-pass beam, no such measurement was performed and the energy was computed from Arc measurements taken for 4- and 5-pass beams and extrapolating to the 3-pass beam. Unfortunately, this leads to a significant inaccuracy which resulted in large uncertainties in the extracted spectrometer angular offsets for this set. Finally, it is possible that the spectrometer absolute angular offsets change with time due to other factors and there were other (more extensive) ep scans performed later to study these changes but they have not yet been analyzed.

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