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. http://ipnweb.in2p3.fr/~detect

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)

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

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

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

Test of the FIFO Inter-event times => noise 1 and 3 kHz / PMT @T ≈ 25°C, 0.9-1.8 kHz / PMT @ 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

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. 4000 ADC ch.)

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

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

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)