09March06 Sasha Notes on Alternative Inflight Calibrations

Alternative In-flight Calibrations (Sasha and Eric)

• Proton Calibrations
  • It looks like we are rather limited in statistics of GCR, even with carbon - to get 1000 hits per crystal (without any angular or position selection) we need 2-3 days. With iron this number is ~200 days. Without selection the pathlength is rather sensitive to position measurement, so the error in position measurement could significantly broaden (and bias) the energy deposition peak even after pathlength correction. This means that even with carbon we should wait for few days (may be ~10 days) until we get the calibration. Another problem with GCR calibration is that we cannot test the procedure on the ground, so we'll definitely find some problems at the beginning.
  • It seems reasonable to use the alternative method of calibration, similar to what we are doing now, using protons to calibrate LEX8 range and any background energy depositions to intercalibrate other ranges and propagate the calibration from 12 MeV up to 70 GeV. Intercalibration of ranges with background energy depositions could be also used together with carbon peak measurement to propagate calibration from 500 MeV to higher energies (without using iron peak which requires much longer period of time to get reasonable statistics).
  • In order to collect protons we need to define a special mode of operation, when we "invert" the ACD veto (require the presence of ACD signal in the ROI), select only "clean" protons by onboard filter and prescale them to make the event rate acceptable for sending them to ground. These protons could be then processed by the same calibration procedure (calibGenCAL) as we use now for muons. We probably can just implement in the onboard filter the selections of "vertical" protons, used now in calibGenCAL(coincidence of
    4 crystals in the same column) - this will allow us to send only necessary proton data to the ground. Note that, unlike heavy ion calibration, this is a special, non-science operating mode.
• Range Intercalibration
  • To intercalibrate the ranges ( as we did with GSI heavy ion data, for
    example) we need 4 range readout. This requires a separate trigger engine which accepts events with sufficiently big energy depositions in CAL (for example, containing CAL_LO trigger bit) and prescale them by appropriate factor to keep event rate reasonable. Simulation is needed to estimate the expected event rate.