GERDA - the Search for neutrinoless double beta decay
Prof. Peter Grabmayr (Universität Tübingen)

The GERDA (GERmanium Detector Array) experiment searches for the neutrinoless double beta decay of ^{76}Ge. The neutrinoless double beta decay is a lepton number violating process and if observed would prove the Majorana nature of the neutrino. It then would lead to physics beyond the Standard Model.
GERDA is located at the Laboratori Nazionali del Gran Sasso of INFN and operates enriched Ge detectors directly in liquid argon. The liquid argon acts not only as cooling medium, but also as passive (Phase I) or active (Phase II) shield against external radiation.

After a successful completion of GERDA Phase I in 2013, that resulted in a lower limit on the half-life of ^{76}Ge > 2.1 10^{25} yr (90 % C.L.) the experiment was upgraded to double the target mass and significantly reduce the background level. Newly designed Ge detectors were installed along with a veto system detecting the liquid argon scintillation light.

Results from Phase I, expectations from present data and competitors will be discussed.