Optics Meeting April 19 2022 230PM ET

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1. Quick blocker material update [1] - Kate

2. Singles rates at GEM (David)

3. Algorithm development (Hanjie, Vassu, Kate)

4. Some initial Plots with New sieve geometry (Vassu, Kate, Zuhal, Hanjie) [[2]]


Bill, Kate, Vassu, Hanjie, David, Chandan, KK, Brynna, Ciprian


1) There appears to be a factor of 2 increase in the rate of electrons seen at the main detectors for the 90%W/10%Cu version of the blocker compared to a 100% W version (with identical geometry), using the elastic 12C generator. This seems a bit unexpected. Not clear it is a real problem - need to compare to the "unblocked flux" to see if the absolute numbers are relevant. Should compare similar thing for the Moller generator on hydrogen target. For tracking measurements, a "punch through" fraction at the 1% level or smaller should not be a problem; for the blocker studies in integrating mode, want punch-through <0.1%. Need to check energies of the punch through electrons, improve the statistics. We also worry (for the integrating mode) about gamma-rays at the main detectors, as they can provide light in the quartz also; should look at ring 5 in this case as well as ring 2. Might be able to check the relative effect of 90/10 vs. 100 with higher statistics by just looking at the rate of particles exiting blocker with virtual detector at exit of blocker (this detector is already implemented).

2) Singles rates at GEMs: Ciprian has suggested thus use of an alternate Physics List to allow GEANT to properly deal with lower-energy gamma and x-rays: [3] "Low Energy Electromagnetic Physics - Livermore". Bill has checked, this should enable simulation down to, for example, 250 eV for photoelectric effect - this gets into the region we are worried about, 250 eV -> 50 keV, where photoelectric cross section on Ar is very high. Bill has found were in remoll to add new physics lists. Should probably try two things: just adding the low-energy photoelectric list, and adding all the low-energy lists in the Livermore list, see the effect on CPU/event and on low-energy gammas at the GEM location. If we do see significant problem, KK suggests we look at vertices to see where the x-rays are being generated. Bill/Kate will work together to try to generate first such simulations.

3) Kate has generated simulation rootfiles for 12C generator at various beam energies with a full annulus version of the sieve (to avoid edge effects), and with 15 different hole locations. Vassu has new results from these simulations - after discussion, they all seem to match our intuition. Hanjie takes up her new position today, Zuhal will lead the algorithm effort from now on (Hanjie will continue to participate in the meetings).

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Meeting ID 970 3027 1000

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