The calibration system of the GERDA muon veto Cherenkov detector

The GERDA experiment searches for neutrinoless double beta decay ( 0 ν β β ). To achieve a sensitivity of 10 - 3 counts / ( keV kg y ) or better within a specific region of interest (ROI), a good background identification is needed. Therefore GERDA is located in the LNGS (Laboratori Nationali del Gran Sasso) underground facility. In addition to the good rejection of cosmic muons due to the surrounding bedrocks, a dual muon veto system has to be used. For calibration and monitoring of the muon veto, two separate systems have been developed.