Characterization of the Aging and Excess Noise of a Hamamatsu Fine Mesh Photopentode

The excess noise factor and the aging characteristics of 16 Hamamatsu R11283 photopentodes have been tested. These fine-mesh phototubes are to be paired with pure CsI scintillation crystals considered for use in the endcap calorimeter of the Belle II detector. The average excess noise factor was found to be $1.9 \pm 0.1 \pm 0.4$. The electronic noise of a custom preamplifier produced by the University of Montreal was found as a consequence of this measurement and was $1730 \pm 33$ electrons, in agreement with previous values. On average, the gain$\times$quantum efficiency was reduced to $93\pm3$ % of the initial value after passing 7 C through the anode. This corresponds to 70 years of standard Belle II operation.