Precision Measurements of Time Characteristics of ETL9351 Photomultipliers

The measured characteristics of 2200 photomultiplier tubes (PMTs) for the future Borexino experiment are considered to provide the most complete information for evaluating the time characteristics of ETL9351 PMTs with a high precision. The unique time characteristics of the apparatus used and the large statistics obtained during the tests of the PMTs allow the fine structure of the PMT time response to be resolved. A method for obtaining the probability density function of the single-photoelectron counting from the experimental data is proposed and used to derive the PMT average characteristics. For the first time, an analytical model is proposed to describe all the features of the single-photoelectron PMT time response. The origin of small-amplitude pulses, as well as the shape of the time spectra of PMT, is explained.