Compton Meeting, February 14, 2011

Attendance

Kent, Dipangkar, Amrendra, Mark, Vladas, Wouter (minutes), Dave (chair)

Minutes

• Only last few days we had good beam
  • before that, bad background, flucts in norm scint by factors
  • since Friday/Saturday we have better conditions, S/N of 50%

• CPslow keeps locking up
  • memory issue? need to run memtest on it at next access
  • pictures of every lock-up would be useful
  • hcreboot switch from GEM will be used for Compton
  • Don set it up to reboot on exception error, not tested yet

• Electron detector
  • presentation by Vladas (elog 151)
    • efficiency of ~8% for plane 1, ~2.5% for planes 2 and 3
    • efficiency-corrected population per strip looks reasonable
    • Compton-edge at strip 48, or 1.74 cm (according to Mark & Jay's calculation)
    • strip 0 is approximately half-way between rho = 0 and rho = 1
    • now 3.6 mm away from beam?? should be 8.5 mm to strip 0, so maybe 7 mm, but then guard strips, and first 4 strips are connected to ground... so maybe 6 mm
  • presentation by Amrendra (elog 150)
    • looks good
    • today will swap the cables
    • DD: different from Dec 10, now more hits on strips 0-32
    • should figure out what to do on 0-32, then repeat efficiency studies on this run
    • background-subtracted and background on hclog 220185, odd channels lower due to being read out on one side, should be taken into account when efficiency is calculated on these runs
  • Amrendra: 4mm away from beam, is this safe?
    • in IR, no large excursions when looking at EPICS during beam recovery
    • it has survived beam trips already, so probably OK
    • should have taken out for Moller measurement today probably
    • general feeling that it should be safe unless wild things happen
    • harp scans upstream? no difference with being in garage... so also acceptable
  • if access, need 10 mins to push QWADs

• Laser
  • fine, apart for unhealthy CPslow
  • locking at 700W
  • time to go down? no, would need longer time

• Photon detector
  • signal path, see elog 56
    • QDC is in data stream, only first QDC entry should correspond to the snapshot in the helicity event
    • threshold now 20mV for un-amplified signals coming up
  • shift of baseline
    • shifts in baseline from tunnel are large even in ms interval
    • pedestal shifts are not caused by the ADC itself, eliminated by Don's studies
    • phosphorescence in CsI(pure), see paper, evidence on 5-10s timescale
    • similar to what has been seen before at 20min timescale?
    • does correction as Don is doing right now taking care of this?
  • plans
    • Zener'ize the bases, characterize the tube, glue on to spare crystal
    • test: mini-megan, or detector group lab
    • build mini-megan into photon detector, Don has all the pieces
  • old tube still has the peak
    • probably not activation
  • need to evaluate background by looking at pedestal more carefully
  • amplifier in tunnel: what did we learn?
    • should set up amplifier system upstairs before moving it downstairs

• Analysis
  • accum0 are not in MPS tree but are in HEL tree
  • QDC is not filled...