Gain settings for the upgraded H.E.S.S. CT1-4 cameras under moonlight observations

The purpose of this technical document is to assess the effect of a gain reduction on low- and high-level analysis results and to investigate the option of using a common lowered gain for both, dark and moonlight observations. Using a sequence of six Crab Nebula runs taken at alternating gain settings, it was shown that decreasing the gain factor from 80 to 60 Analog-to-digital counts per photo-electron (ADC/pe) has no significant effect on the telescope system sensitivity under dark-sky conditions. This result confirms expectations that such a change in gain has a comparatively small effect on the signal readout. In particular, the following results were obtained: 1. The trigger rates and event statistics are comparable for both gains. 2. The distributions of Hillas parameters are consistent for both gains. 3. The spectral analysis results are consistent within about 10%. The efficiency of detecting gamma rays is energy-independent and consistent for both gains, indicating no loss of performance at any energy.