Optics Meeting Mar 6 2024 1100AM ET

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Agenda

1. OpticsMatrix fitting in c++ (Tyler)
2. interactions in GEM frame and ribs (Daijon)
3. kinematic factor (Vassu)

Attendance

Klaus, Daijon, David, Kate, Tyler, Sayak, Mike, Zuhal, Chuan Sun, Hanjie, Andrew, Kent, Vassu, Juliette, Buddhika, Paul S

Minutes

1. (Tyler) Has new C++ optics matrix fitting code running for initial tests; on githib. There is a README for people wanting to run on a Mac with a newer (M1 or M2) chip. Using the "slimmed" simulation rootfiles as input, initially from 12C pass 3 simulated data from single carbon foil. Aside: there are about 65,000 events in the the file; the only selection criterion for the slimmed files are that the primary events make it to the main detectors. Can select to fit to extract either theta or phi. Can allow the fit to find the best functional form (which polynomial powers) to use. At the moment, trying to reproduce fits from Vassu's chosen functional forms. Theta fitting looks reasonable, although has tails in the residuals due likely to not having (yet) excluded radiative tail contributions. Phi fit not working, but probably due to an offset in phi angle definition (-pi to pi vs. 0 to 2pi); might also move to fitting phi local. Question - should sieve hole locations be hard-coded? Kate suggests not, at least for now, as her magnetic field imperfection studies require her to "rotate" the sieve in simulation, so best to leave the sieve geometry to be read from input file.
2. (Daijon) Looking at remoll simulation for Moller events with virtual detectors for the GEM frames and ribs. Some confusing initial results which seem to be because of the same detector number being used for a virtual detetor that is not associated with the GEMs. Suggested that we should choose detector numbers that are unique.
3. (Vassu) Continuing investigation of the kinematic factor determination. The basic idea is, for simulated MOLLER events (no sieve) to use the theta determined from the fits to the GEM data, and the known one-to-one relation for MOLLER events between theta an E' (for given E) to get the "y = E'/E" which is used in the kinematic factor calculation. Initially, are comparing the "true" KF as determined from a) the E' immediately after the vertex and the beam E just before the vertex and b) the KF determined from the exactly 11 GeV incident beam energy, and the theta after exiting the target, at the sieve entrance. After discussion, it seems that a) is being "smeared" because of the effects of the raster - the raster initial angle of the beam is not directly along the beam axis, so the scattering angle of relevance (i.e. that determines the E') is not simply the scattering angle relative to the beam axis - this adds about 1 mrad of smearing. Plan is to calculate the corrected theta to confirm this. Discussion also of the effect of pre-vertex radiation and energy loss; Kent suggests one could select only events in the simulation that scattered from the first few cm of the target to suppress this effect for initial studies.

Meeting link information

See email invitation, or contact David Armstrong, Kate Evans, or Jennifer McAllister for Zoom link