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Present: A. Deur, M. Dalton, S. Sirca, J. Stevens.

  • We discussed what questions need to be answered by the simulation, based on Justin's document.
    • In addition to the questions in the document, the MC will help finding the optimal experimental set-up.
  • We discussed the possible virtues of flipping the target spin and and reversing the beam helicity assignment with the beam 1/2-wave plate
    • Reversing the beam helicity assignment is not useful except for sanity check.
    • There is no single-polarization asymmetries for photoproduction reactions (in contrast to electroproduction). Thus, no contamination can arise from this even if the azimuthal symmetry of the detector is not perfect. In any case, GlueX data show that the detector azimuthal symmetry is very good.
    • Polar asymmetry of the detectors may induce a bias in the data if the σ1/2 and σ3/2 cross sections have different polar angle dependence. This is minimized (and can be corrected) by binning the data in fine enough angular bins.
    • RF-flipping the target spin once in the experiment to get two data set of opposite raw asymmetry sign will ensure than the above asymmetry (and other possible ones) cancels when the two data sets are combined.
    • Although there is no expectation of significant false asymmetry, RF-flipping the target spin is relatively easy and fast (1/2 day?) and it will add robustness to the final result. So it should be included in the experiment.
  • Discussion on target length:
    • A longer target will enable running at less current and thus creates less tagger accidentals
    • What maximum target length fits in the present Start Counter (ST).
    • Do we need a ST?
  • Discussion on the Pair Spectrometer (PS):
    • Should we upgrade the PS so that we cover the low γ flux?
    • This can be done by adding detectors at larger angles.
    • It can also be done by moving the detector closer, although we would loose resolution. But since we do not care about coherent peak, or worsen resolution may be acceptable.
  • How well can we check beam charge asymmetry with BPMs?
  • Marc Dalton will look at the effect of a beam position-helicity correlation on the data.