Optics Meeting Mar 14 2023 230PM ET

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  • Hole selection for the θtgt fitting: [1]
  • Initial look at plotting the kinematic factor for MOLLER events: [2]


Kate, Sayak, Ciprian, David, Andrew, Zuhal, Vassu, Paul S., Tyler, Juliette


  1. (Vassu/Zuhal) Have automated the method to select tracks that went through particular holes for use in the optics fitting. Uses rate-weighted distributions of radial position at GEM, does Gaussian fits over selected regions for regions where tracks from a given hole (for 12C elastic) are expected. Finds mean of Gaussian, and then selects events within +- 2 sigma of mean as good tracks. For sectors (holes 71 and 72) where the holes are at the same r in a given sector, it instead does similar fit to the phi distribution. Could extend to a 2-Gaussian 2-D fit of (R,phi), but that is probably not required.


  1. (Zuhal) Initial look at plotting the kinematic factor for MOLLER events, for primary electrons in Ring 5, based on the exact ("thrown") kinematics of the simulated events. Next, could look at using reconstructed kinematics.
  2. (Kate) Has GDML code working to rotate the sieve to different sectors - [3]. Working on tracking results for these various combinations.
  3. (Andrew) - simulations with multiple layers of GEM frames are waiting on some input from Bill
  4. (Andrew) - started work on hyperon generator; has made an ad-hoc phase space generator, and compiled some data on photo- and electro-induced hyperon cross sections. Will update at next week's meeting.
  5. (Juliette, all) The worst case B field simulation we have used is one which generates largest dipole, within our tolerances of +/- 1mm coil displacement at inner radius and +- 3 mm at outer radius - this field map still produces acceptable asymmetry changes in ring 5. So, the fact that we can "see" evidence for this field map in the tracking data is very good - we should be able to put limits on such field distortions being in the acceptable range based on tracking data (as long as we are not blind due to a particular orientation due to the sieve pattern, i.e. what Kate will be checking).
    1. According to the spectrometer System Requirements Document (SRD), the sieve hole machining tolerances will be 0.1 mm. The positioning tolerance in Z is loose (+/- 3mm), the alignment with the beam axis is +/- 1 mm and the alignment in phi is +/- 0.2 degrees (this corresponds to an offset in the phi direction of 0.2 mm of hole at the outer edge of the sieve. A miss-positioning in r will affect our ability to see distorted magnetic fields using Kate's approach... but survey of the actual sieve location should give results better than 1 mm, and any offset from central axis would show up as uniform shift of the sieve pattern, different than what a distorted B-field would give, and which could be identified and corrected for in tracking analysis.
    2. It seems likely that additional holes, just for B-field checking with tracking, could be added at small radius and large phi offset in one or more sectors. These should produce tracks at large R at the GEM for 12C elastics (and off the acceptance for Moller events), so are unlikely to contaminate our "optics holes". Vassu will propose some additional holes. They could be smaller in diameter (5 mm?) than the optics holes, if need be. He is also looking at making holes 41 and 61 smaller in diameter to avoid overlaps with tracks from other holes in those sectors.
  6. (Juliette) While not on the priority list (i.e. not needed for the CD3a purchase of the sieve) it would be great to see if we could use tracking data not only to show that the B-field is not grossly wrong, but also to provide input to how to adjust the coil locations in the Tosca B-field calculation, so as to generate a more correct field map for tracking and simulation.

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Meeting ID: 972 5975 5403

Passcode: 4937

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