Speaker
Description
Muons created in extensive air showers in the lower atmosphere can leave ring-like traces in the images recorded by imaging atmospheric Cherenkov telescopes (IACTs). These traces can be used to monitor the optical throughput of an IACT via the so-called muon efficiency, a parameter calculated from the radius and brightness of these ring-like traces.
The standard calibration chain of the H.E.S.S. Experiment includes the calculation of the mean muon efficiency for each telescope and observation, yielding >20 years of detailed muon effieciency data. These time-series show the overall degradation of the optical efficiency due to hardware aging of the H.E.S.S. telescopes and also depict the sudden upward jumps as the mirrors or cameras underwent maintenance.
Besides these expected changes in muon efficiency, a residual variation on an annual scale can be observed which is so far not well understood.
This contribution presents a study that investigates these variations in detail, probing correlations to atmospheric as well as other observation conditions and outlines potential implications for IACT calibration procedures that rely on muon efficiencies.