C. Langbrandtner

Afterpulse measurements of R7081 photomultipliers for the Double Chooz experiment

We present the results of afterpulse measurements performed as qualification test for 473 inner detector photomultipliers of the Double Chooz experiment. The measurements include the determination of a total afterpulse occurrence probability as well as an average time distribution of these pulses. Additionally, more detailed measurements with different light sources and simultaneous charge and timing measurements were performed with a few photomultipliers to allow a more detailed understanding of the effect. The results of all measurements are presented and discussed.

PMT Test Facility at MPIK Heidelberg and Double Chooz Super Vertical Slice

The two inner detectors of Double Chooz (DC) [1] will both be observed by 390 photomultiplier tubes (PMTs) to record light pulses produced by neutrino induced reactions inside the scintillator volumes. The task of calibrating the PMTs was shared among DC Japan and MPIK/ RWTH Aachen. At Heidelberg a test facility was built which allows to calibrate 30 PMTs simultaneously. The VME based data acquisition (DAQ) includes devices for charge spectrum recording, for time measurements and scalers for dark rate counting. The PMT calibration campaign encompassed the determination of the single photo electron (SPE) gain and resolution, transit time spread and linearity for multi-PE events. Two trigger boards developed by RWTH Aachen were integrated to test their performance and to examine afterpulse probabilities and dark rate counting. The derived results were translated into time and charge probability density functions (see fig. 1), which in turn were implemented into the Double Chooz Monte Carlo simulation. The Super Vertical Slice (SVS) is an upgrade of the PMT test facility. It consists of the complete and original Double Chooz electronics plus an acrylic vessel of 30 liters filled with the Gadolinium doped ν-Target scintillator. The electronics consists of PMTs, high voltage (HV) power supply, HV splitter, frontend electronics (FEE), trigger system (TS), waveform digitizers (WFD) and DAQ. It has been successfully used to finalize the interface of FEE and TS, such as signal gains, and to control the quality of the final FEE production. The electronics response in case of very high energy depositions has been studied. The obtained results hint at the feasibility of using muon-induced isotopes, such as 12B or Michel electrons, for detector calibration. The SVS has been first to record pulses from the original ν-