Oct 14, 2019
Agenda: Progress and systematics discussion: Don [slides]
Meeting URL https://bluejeans.com/388466836
Meeting ID 388 466 836
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Attendees: Don Jones, Paul Souder, Bill Henry, Dmitrii Nikolaev
See talk linked above. Key discussion points:
- Ideal to see Levchuk correction mapped out including both sides of peak and over flat region for CREX
- Don showed Eric's slides on 2,4,6,and 8 PMTs and stated that the "flat region" was just as good or better for the 6, 4, and 2 PMT solutions as it was for PREX (gray boxes on slide 3 are 10% in Q1 current and 0.5% in Azz). He also suggested there was not a compelling reason for taking the 4 PMT solution over the 6 PMT based on these plots. You lose rate for no gain in "flatness". He also pointed out that we will likely need a 10-12% overtune for Q1 to get to the flat region.
- Paul replied that the 6 PMT was just letting in a wider acceptance of theta and introduced more uncertainty. "Why would you want to let in more junk?"
- Don argued that this was a nice qualitative statement but that the quantitative curves seemed to indicate that letting these in did not produce more sensitivity or lack of flatness.
- Paul asked why you would ever want to do this since you can get all the rate you want but just using the thick foil and turning up the current.
- Don answered that it was plausible that activation downstream could impose an upper limit on the current as before. In this case, if there were no advantage to rejecting part of the Mollers by turning off two PMTs then why not keep the additional 30% in rate?
- Both agreed that we would have to wait to see how things turned out when we tune up the beam. We should be ready for either case.
- Even if we don't think we are sensitive to the Q1 tune during a saturation test, we should test that at least once at the lower limit of the scan (2.5T) by doing a Q1 rate scan to reoptimize Q1
- Should plan on an optics scan to measure the offset of the solenoid. Solenoid reversal would be a nice systematic check, but without knowing the misalignment of the optics it won't be interpretable.
- Agreed it would be nice to verify key claim of insensitivity to Q2/Q4 by under/over tuning them and re-tuning relative to Q1 max then taking precision asymmetry data
- 11 GeV discussion
- Eric has been doing studies in prep for possible 11 GeV but could not make the meeting. Look for discussion later.
- Dipole current maximum is 440A which may not get the full Moller distribution on the detector (the top may be cut off). Can we get a new power supply to go higher?
- Also, all the Mollers are essentially contained in the top two PMTs. This detector is not ideal for 11 GeV
- Paul thinks that a new collimator is irrelevant since it would have to be placed after uncertain optical elements and would thus not be precisely defining. He believes we will get all the information we need with a precise set of GEMs.
- Need to simulate and study our ability to map out radiative corrections, Levchuk corrections and Azz as a function of position and angle to inform design decisions for the Lab soon.
- Bill reminded us that we have quad scan data at 11 GeV in hand from DVCS