Speaker
Summary
The neutrinoless double beta decay is a lepton number violating process and if
observed would prove the Majorana nature of the neutrino. The Germanium Detector
Array (Gerda) experiment, located in the Gran Sasso underground laboratory, Italy, was
constructed to search for the neutrinoless double-beta decay of 76Ge. HPGe detectors, isotopically enriched
in 76Ge, are operated bare in liquid argon. Phase I was successfully completed with a
new lower limit of T1/2 > 2.1 · 10^25 yr (90% C.L.) achieving the aspired background index
(10^−2 cts/keV·kg·yr) in the region of interest. For Phase II the active detector mass
has been doubled and an argon scintillation light veto system has been deployed. The
expected sensitivity (with a background index of 10^−3 cts/keV·kg·yr) is T1/2 > 1.4 · 10^26 yr
with 100 kg·yr of exposure. After the extensive upgrade Gerda has started data taking in
December 2015. The detector array performance and first Phase II data will be presented.
