42Ar/42K background in the GERDA experiment

The GERmanium Detector Array experiment is designed to investigate the neutrinoless double beta decay in 76Ge at a Q-value of 2039 keV. The roadmap is separated in two phases; Phase I, with an expected background of 10-2 cts/(keV .kg .y), is able to probe the claim of the Heidelberg Moscow experiment within one year of data taking. Phase II, with an aspired background of 10-3 cts/(keV .kg .y), could probe the inverted hierarchy scale. The recent start of data taking with a test array showed, however, an unexpected high contribution of 42K to the background. With a Q-value of 3525 keV, this progeny of 42Ar could pose a thread to the novel idea of operating bare HPGe detectors in liquid argon. In this talk, Monte Carlo studies are presented that investigate the origin of the 42K background and the unexpected high concentration of 42Ar (42Ar/40Ar ∼4 .10-20). It is shown that the comparison of simulation and experimental data favours charge collection of 42K as an explaination. In addition, further simulations are presented that go hand in hand with various experimental runs with different electric field configuration in order to alter the position and concentration of 42K decays and provide hints for solutions of 42K background reduction.