Single electron charge spectra of 8-inch high-collection-efficiency MCP-PMTs

The microchannel plates (MCP) can serve as the electron amplifier of the photomultiplier tubes (PMT). The collection efficiency of the newly developed 8-inch MCP-PMT for the Jinping Neutrino Experiment is maximized thanks to the high-secondary-emission coating. The resulting single electron response (SER) charge distribution deviates from the Gaussian distribution in large charge regions. To understand the nature of the jumbo-charged SER, we designed a voltage-division experiment to quantify the dependence of the MCP gain on the energy of incident electrons. Combining the relationship with the Furman probabilistic model, we reproduced the SER charge spectra by introducing an additional amplification stage on the input electrode of the first MCP. Our results favor a Gamma-Tweedie mixture to describe the SER charge spectra of the MCP-PMTs.