General Meeting Summary 4/30/15

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  • Transmittance measurement results for 10 SIC crystals manufactured in 2014
  • Note that wavelengths of importance for NPS are ~400nm
  • At 420 nm the spread in crystal transmittance is on the order of 20% - may indicate that need many spares if go with this option
  • Light yield measurements
  • NPS prototype is being optimized for these tests with nine PWO crystals. Optimizations include better isolation between crystals to minimize cross talk etc.
  • Initial measurements with cosmics found a much lower light yield than the one reported by Rainer with 1 MeV photons
  • Shipment of five PWO crystals to Rainer is still pending
  • awaiting final signatures


  • Discussion about UVa target capabilities
  • Based on previous studies the optimal way to run the target with electron beam is at currents of 80-90 nA. The reason for this is an increase in inefficiencies due to, e.g., heat load of the beam, polarization damage, increase of radiation damage and so more frequent annealing, etc.
  • There are plans to improve the target including continous annealing, longer targets, etc. that may allow for running at higher beam currents. For the LOI it would be best to use the known optimal numbers and mention these improvements in the experimental section.
  • Discussion about possible optimizations and modifications that may allow for increasing beam currents in the TCS setup
  • Target magnet: current magnet has +- 18 degrees acceptance in forward direction for transverse target. It may be possible to use a solenoid that can provide this range. This would require a suitable chicane as well.
  • Beam dump: TCS needs a stiffer beam than the polarized WACS experiment - the current design would not work
  • Physics case: acceptance studies ongoing. These will be used to estimate the impact of the experiment data on global GPD fits
  • a discussion of recent updates of the form factor parameterization in the fit model should also be included
  • Experimental details
  • current configuration envisions NPS-type detectors on right and left hand side of the beam line, but there are still some optimization questions left, e.g., proton acceptance and target polarization. Goal for LOI is to demonstrate that the physics is compelling, that there is a reasonable count rate for the preliminary configuration, and that there is sensitivity to the physics of interest. The LOI willl
  • the LOI will focus on the instrument, i.e., the NPS, and the transverse polarized target rather than a specific experimental hall.
  • Action Item: circulate LOI draft for comments on target (Donal) and acceptance (Rolf)


  • TCS LOI for PAC43 - if needed
  • Crystal studies at JLab and Giessen
  • Other...