  Photomultiplier tubes (PMTs) are widely used in neutrino and other
experiments for the detection of weak light. To date PMTs are the most
sensitive single photon detector per unit area. In addition to the quantum
efficiency for photon detection, there are a number of other specifications,
such as rate and amplitude of after-pulses, dark noise rate, transit time
spread, radioactive background of glass, peak-to-valley ratio, etc. All affect
the photon detection and hence the physics goals. In addition, cost is another
major factor for large experiments. It is important to know how to properly
take into account all these parameters and choose the most appropriate PMTs. In
this paper, we present an approach to quantify the impact of all parameters on
the physics goals, including cost and risk. This method has been successfully
used in the JUNO experiment. It can be applied to other experiments with large
number of PMTs.

Instrumentation and Detectors;High Energy Physics - Experiment