Optics Meeting Jun 14 2022 230PM ET

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1. vz reconstruction (Vassu)[1]

2. Understanding the scattered electron energy vs gem_r plot (Vassu) [2]

3. Livermore into Remoll [3]


David, Bill, Kate, KK, Ciprian, Vassu, Brynna, James, Nathan


  1. New participants from SBU: James will be working on GEM analysis code, Nathan on GEM prototype; Brynna will be moving to work on the SBU gas handling system.
  2. Kate and Vassu will jointly give Optics/Kinematics talk at next week's collaboration meeting.
  3. The absolute positioning of the sieve collimator will be checked in the experiment using B-field off data and the downstream scanner.
  4. Vassu: v_z reconstruction shows promising results with the 5-pass beam with the 12C elastic generator. By using the reconstructed theta (at the sieve) and the true R_sieve, simple geometry allows extraction of v_z. While this will get fuzzier when we use reconstructed R_sieve, presumably, it should still work. With two 12C foil targets located 30 cm apart in Z, for certain sieve holes can clearly identify the correct foil from the v_z plots. For holes at smaller radii, the two foils start to overlap, the v_z residuals bifurcate, and the fit is randomly choosing between them. This may provide a reason for ensuring that we have enough sieve hole positions at large radii. We should try two sets of two foils for optics target locations, perhaps one set of two being one at the upstream end, and then one 2/3 way down the target, and the other set being one 1/3 of the way down the target and one at the downstream end. A small effect to consider is beam energy-loss in the upstream foil changing the response from the downstream foil - to check that, may want to use the beam generator (hard to do using the 12C generator in one simulation). Also, would want to look at whether our optics reconstruction would be "bothered" by Moller events; beam generator would also tell us that. Another thing to look at is whether we can/should use smaller diameter holes (0.5 cm?). This should tighten precision of optics, unless slit-scattering gets worse.
  5. Vassu: Looked more at scattered energy vs. GEM radius plot puzzle. When looking at E' (just after the scattering vertex) vs. r_GEM, can see the horizontal line which is likely due to radiative processes in the target after the scattering, and a falling band which is likely radiative processes for the electron before the scattering. However, when looking at the E for the primary electron at the GEM location, we see the falling band (pre- and post-scattering radiation in the target, as expected), but also a vertical band which is not understood. These are electrons of lower energy when at the GEM, but that still arrive at the nominal unradiated radial location at the GEM. How? Vassu has checked that they don't appear at earlier stages in the flight-path, but somehow manifest in front of the GEMs. Drift tube exit window? That should not provide this high a probability of hard bremsstrahlung. Some other scraping? Ideas to investigate - add more virtual detectors in front of and behind the exit window. Look at R, Phi or x,y distributions for these events upstream of the GEMs. Maybe look for energetic bremss photons at the GEM plane, and look for where the photons were generated(using hit.vx, hit.vz, hit.vy) for these photons. Also, should check that the pre- and post-radiation probabilities in the 12C target make sense.
  6. Bill: previous attempt to modify remoll physics lists to better simulate low-energy gammas and x-rays didn't work, the Livermore EM list was in fact not loaded. Bill now understands how to do this, however, simulations also including low-energy ionization take forever to run, so will probably need to turn that process off. Testing is underway - Kate will generate new simulations soon.

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Meeting ID: 972 5975 5403

Passcode: 4937

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