Jan 21, 2018
Hardware/onsite update, Simona
Geant3 optics solutions, Bill
Geant4 update, Eric
Meeting URL https://bluejeans.com/388466836
Meeting ID 388 466 836
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All the surveys are done and that we will be cooling down the target magnet for tests this week. The survey group is very busy with work in the Accelerator and in the halls but they said I will have all the survey results by the end of this month. I will make a new branch of the Hall A moller polarimeter on the wiki and post all the new stuff - I hope to have this done by next Monday.
I will also take few LED runs to make sure the daq looks good before we close the hall. Yves is working on the details of the beam deflection test. We can discuss how to staff the commissioning shifts next Monday (I will show how I would think to do it).
Bill Henry showed results that provide an estimate of a ~0.05% shift in Azz from a ~0.2mm position shift in x or y. Without FFB on I don't think we can rule out mm level wanderings. This could potentially be a significant source of systematic error. We need to determine whether or not FFB can/should remain on during data taking.
Follow up questions: 1. What about helicity-correlated position differences that could contribute to a false asymmetry? Looking at Bill's figures I would estimate a change of about 0.3% in coincidence rates from a position shift of 0.2 mm. Assuming 100 micron HC differences in this region (is this reasonable?) then gives a false asymmetry of 0.15%. Our measured asymmetry is about 5.5%. This is a potentially significant issue. 2. Can FFB be activated at 1 muA and would it be helpful to reduce
Eric King showed some more G3 G4 comparisons with significant differences in the quad scan region. We decided to do one more ray trace comparison to try to decipher cause of differences. Eric is moving on to investigating various optics solutions including one close to Dave Gaskell's solution and Bill's solutions. He has also been tasked with finding a set of quad scans at 2.2 GeV that will be useful for simulation calibration/verification that we can run in the March post APEX run periods.