1. B. Genolini for the IPNO detector dept.
PMm2
Preliminary measurements with the PMm2 demonstrator Videoconference – Orsay – Sept. 16, 2010
B. Genolini for the IPNO detector dept.

2. Settings
Minimum charge that can be detected = 106 electrons => minimum gain = 3.106
Voltage set accordingly (all the PMTs at least working at a gain of 3.106): 1550 V
Set the discriminator just above the noise level (380 DAC channels)
PMT gain compensation applied
Measurement in July: temperature above 25°C
Measurements in September: temperature around 20°C
DAQ: program by B.-Y. Ky (C#, Windows)

3. A noise histogram Discriminator threshold (0.3 p.e.)
Single electron peak
Events below threshold
High gain histogram
Low gain histogram (rescaled)
Events below pedestal

4. Possible coupling ? Dashed = no selection on the events
Full line = without coincidence during the coarse time stamp (100 ns)

5. Noise induced DNL ?
DNL not observed during the measurements with a single channel
Events below threshold
DNL, not statistics
(≈ 10,000 events / bin)

6. Test of the FIFO Inter-event times => noise
1 and 3 kHz / ≈ 25°C,
kHz / T ≈ 20°C (with possible remaining light leak)
Charge vs inter event time:
Before 20 µs: dominated by the afterpulses
Early afterpulses (< 2 µs) up to 20 photoelectrons
Peak at 7 µs
To be compared with the 100-µs time for the full readout
Performance in noise relatively stable with regards to the magnetic field
Close results with the PMT placed horizontally (noise spectrum P/V and counting rate)
Early afterpulses
Peak at 7 µs

7. LED / high rate LED above Ch. 0 Light leak (>5 kHz)
LED counting rate around 5 kHz
Channels mapped according to their position in the tank
Data below the pedestal on the low-gain ramp when the counting rate is too high?
Lots of reflections on the PMTs
Low gain ADC < threshold / pedestal
Too high values? (equiv ADC ch.)

8. Water: greater counting rate
Horizontal scale: up to 5,000 equivalent high-gain ADC channels
Tap water, 20 cm above the PMTs
Counting rates ≈ 4.5 to 6.7 kHz: lower temperature but Cerenkov effect in the water (≈3 kHz, with muons + electrons?)
No charge above 3200 equiv ADC ch.
Cosmic rays?
Same scale, without water

9. Water / low-gain ADC
Unexpected peak
Unexpected events below the ADC threshold
Apparent strange behavior close to the ADC threshold / physics?
Not related to the rate (ch. 6 around 5 kHz, ch. 9 around 4.5 kHz)
Unexpected events above the ADC threshold

10. Conclusions / To do The demonstrator works!
Apparent coupling / additional noise due to the 16 PMTs working together, with a noise between 1 to 3 kHz
Expected dynamic range = 150 photoelectrons, to be verified by measurements with the LED, installed on the enclosure (Memphyno?)
PMTs fully potted + water in the Orsay tank: tests to start (Memphyno)