Characterization of the Spontaneous Light Emission of the PMTs used in the Double Chooz Experiment
2016
During the commissioning of the first of the two detectors of the Double
Choozexperiment, an unexpected and dominant background caused by the emission of light inside the optical volume has been observed. A specific study of the ensemble of phenomena called "Light Noise" has been carried out in-situ, and in an external laboratory, in order to characterize the signals and to identify the possible processes underlying the effect. Some mechanisms of instrumental noise originating from the PMTs were identified and it has been found that the leading one arises from the light emission localized on the
photomultiplierbase and produced by the combined effect of heat and high voltage across the transparent epoxy resin covering the electric components. The correlation of the rate and the amplitude of the signal with the temperature has been observed. For the first detector in operation the induced background has been mitigated using
onlineand
offlineanalysis selections based on timing and light pattern of the signals, while a modification of the
photomultiplierassembly has been implemented for the second detector in order to blacken the PMT bases.
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