Eugene Chudakov wrote:
Pine.LNX.4.64.0905202002260.9321@jlabl1.jlab.org">One can look from another angle. The spectrometer can measure the full energy of the event, assuming nothing is missing. I estimated the RMS of about 0.2GeV for some class of events (any comments?). Taking +/-2 sigmas gives 0.8GeV of the energy interval. This is about the "microscope" width. There seems to be an order of magnitude left out here? For a reconstructed event resolution of 0.2 GeV (200 MeV) and a reduction factor of 2.5 sigmas, I get 80 MeV -- assuming that your 0.8GeV was a typo. Your estimate comes close to the 60 MeV that we say is required for optimal reconstruction of exclusive final states with GlueX. That is not close to the microscope width, however, which is down another order of magnitude at 8 MeV. Pine.LNX.4.64.0905202002260.9321@jlabl1.jlab.org">At the full beam the microscope counts about 300MHz (3 times more than the photon beam in this range, because of the collimator). Assuming the ideal 2ns timing resolution, one gets 60% of the accidentals in the microscope. As far as I understand, this is considered acceptable (treated as a background?). Above 9 GeV the tagger rate per GeV is a factor of 2 lower than at 9 GeV. One may expect a 30% rate of accidentals in the right energy range. As far as I understand, the problem with the fixed array is not the accidentals, but the rate of a single counter, which may be too high for a PMT at the gain required. Agreed. -Richard Jones |
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