2. PMT model
According to A. Kim (JLab) until now there is one published model describing PMTs work in detail. It is described in this paper.
This model did not describe well the results of PMT testing performed by CLAS12 group.
Another model was developed in JLab recently (and is about to be published). This model was applied to the results from H12700 and H8500 testing (single photon mode). It describes the effects well.