Item

Abstract

Photomultiplier tubes (PMTs) are often used in low-background particle
physics experiments, which rely on an excellent response to
single-photon signals and stable long-term operation. In particular, the
Hamamatsu R11410 model is the light sensor of choice for liquid xenon
dark matter experiments, including XENONnT. The same PMT model was also
used for the predecessor, XENON1T, where issues affecting its long-term
operation were observed. Here, we report on an improved PMT testing
procedure which ensures optimal performance in XENONnT. Using both new
and upgraded facilities, we tested 368 new PMTs in a cryogenic xenon
environment. We developed new tests 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 afterpulses, both of which
were observed in XENON1T. We exclude the use of 26 of the 368 tested
PMTs and categorise the remainder according to their performance. Given
that we have improved the testing procedure, yet we rejected fewer PMTs,
we expect significantly better PMT performance in XENONnT.