View source for Optics Meeting Oct 15 2024 0100PM ET

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=Agenda=
# Improved theta determination (Vassu)[https://moller.jlab.org/wiki/index.php/File:Fitting_improvements.pdf]
# Magnetic field imperfection study (Kate)

=Attendance=
# Paul S, David, Sayak, Juliette, Zuhal, Vassu, Kate

=Minutes=
# (Vassu) We have seen that the residuals for the theta determination from a global (all beam energies) fit to the 12C simulated data are smaller when the fit is done for each 12C foil individually than when all 12C foils (at different v_z locations) are fitted simultaneously. With individual foil-fits the sigma of the theta residuals (fitted-true) is about 0.3 mrad, but with the global fit it is 0.61 mrad. When fitting individual foils, the parameters of the fit functions are found to vary smoothly with v_z. Also, the theta_residuals are found to vary smoothly with v_z. So, can we use this to improve the theta determination, even in the case of the real data from the lH2 target where we don't know a-priori v_z? Vassu has shown that we can. He has tested an iterative method in which he first does a global fit to get an initial theta determination for 12C data, then plots and fits the theta residual vs true v_z. Then he uses the initial theta, and the knowledge of the sieve hole radial location to predict the v_z, and using the theta_residual vs. v_z dependence, make a correction to theta by adjusting by the predicted theta residual. He tried up to 5 iterations. In the 12C case this procedure reduced the theta residual for the global fit from 0.6 mrad down to 0.395 mrad. He then applied this same functional dependence to simulated MOLLER lH2 data (with the sieve collimator in), and it seems to work. The sigma of the theta residuals here was reduced from  0.7 mrad to 0.58 mrad. Broader distributions here may be related to the larger number of radiative tail events in lH2 compared to 12C. Looking at how the residuals in v_z and the means of the theta residual distributions stabilize, it seems that only one or perhaps 2 iterations should be all that is needed.
# (David) comment on this; since all the information used is in principle contained in the 4 GEM variables (r,r',phi,phi'), it seems that an ideal fitting function should be able to bypass the iterative procedure, however the challenge is to find the functional form that would do this. I don't know how to figure out what would need to be added to the functional form...
# (Kate) Have had some issues with and older version of Vassu's scripts to get csv files with the hole identification in an  automated manner; Kate has made some script modifications for the W&M undergrad (Evan Jackson). Vassu will send his latest version of the scripts to Kate and Evan. David suggests that these be posted on github; Kate reminds us that there is a MOLLER optics github repository (separate from the remoll github) for this sort of thing.

=Meeting link information=

See email invitation, or contact David Armstrong, Kate Evans, or Ciprian Gal for Zoom link