30.05.2021Photosensor tests for the XENONnT experiment

In this work, a total of 368 PMTs were characterized in liquid/gas xenon environments, thanks to an international collaboration with 4 institutions joining the effort: Stockholm University, University of Zurich, Max-Planck-Institut für Kernphysik in Heidelberg, and Weizman Institute of Science in Rehovot. One current PhD student, Giovanni Volta, and two former students in our group, Dr. Adam Brown and Dr. Julien Wulf, tested a total of 105 PMTs in our laboratory with the MarmotX liquid xenon detector, which can house ten PMTs at a time.  The new tests were targeted at the detection of light emission and the degradation of the PMT vacuum through small leaks, which can lead to spurious signals known as after-pulses, both of which were observed in the XENON1T experiment. The results were used to select the photosensors which were installed in the XENONnT time projection chamber, which contains two arrays with 494 PMTs in total: 253 in the top array placed in the gas phase, and 241 the bottom array in the liquid. The XENONnT experiment is currently under commissioning at the Laboratori Nazionali del Gran Sasso in Italy, with a first science run to start in May 2021. Given the improved photosensors characterisation procedure compared to XENON1T, we expect significantly better PMT performance in the new detector.