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DOM Two Dimensional ScanDOM Two Dimensional Scanningning
using testDAQusing testDAQ
Hiroko MiyamotoHiroko MiyamotoT. NodaT. Noda
Faculty of Science
Department of Physics
Chiba University
Reminder: We did 2D scan for bare PMTs
• CE uniformity : Some tube to tube differences
• Gain uniformity: Almost universal behavior
Implementedby ROMEO
New: 2D scan for DOMs
CE uniformity / Gain uniformity:
• Present: Rely on Geant4 MC + the bare PMT calibration data to predict DOM acceptance. The complex structure of DOM has not been implemented in the MC.
• Easier and more reliable to MEASURE it directly!
2D Scanning System for DOM
Harness
wire
DOM 2D Scanning System
SetupLight Source:• NICHA 375nm UV-LED• 100-200 PEs / shot, fired 1.6kHz by pulser
2D scanning system• Spot size: ~1cm with the collimator• Scan 4 in ~5cm intervals from point to point• Do “testDAQ” ( ‘ready’ and ’go’) at each point.
DOM• Virgo, Rev4• Unsealed DOM, room temperature, ~1atm• TestDAQ : taking data with ~4PE threshold, 1e+07Gain
Analysis Method(preliminary)
(using the java program written by Chris W.)
• Calculate the photoelectron number with domcal Calibration (J.Braun?).
• Use the average of ~3,000 samples for each point of the DOM surface.
Results(preliminary…)
Harness Harness
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Harness Harness
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Results(preliminary…)
HarnessHarness
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Results(preliminary…)
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~25cm
HarnessHarness
Forward region
Backward region
Backward region
Results(preliminary…)
HarnessHarness
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Results(preliminary…)
top topcenter HarnessHarness
Results(preliminary…)
top topcenter HarnessHarness
~25cm
Results(preliminary…)
Summary(Preliminary…)
• Took a first data of DOM photon CE map (along 1 axis).
• “effective” diameter of photon detection area is approximately 25 cm, which is consistent with the PMT cathode area we had measured previously.
• Photons hitting from backside of DOM do not produce measurable signals. To map out this region, we must improve our triggering : currently internal trigger with 4 PE threshold.
Issues to be resolved
• It would be better to trigger DOM EXTERNALY for taking non-biased data – Internal trigger with 4PE threshold may cause bias in scanning backside of DOM sphere.
• Domcal charge estimation may contain some errors in the estimation of the total charge (photoelectron #) of each channels.
• Need to figure out a way to turn off and on data taking without recycling HV power.
Outlook
• 4 measurement and map the CE on the whole DOM surface to be implemented by the detector MC simulation.
• Produce the standard-EYE DOM scanned by this method.
Near future plan
• Absolute calibration of DOM by scattered light from N2 laser : We did for bare PMTs
It would be nicer if external trigger available