Gerda: Results and perspectives

From November 2011 to May 2013, Gerda searched for 0νββ and 2νββ of 76Ge, operating bare in a liquid argon bath Ge detectors enriched up to ∼87% in 76Ge (enrGe), for a total mass of ∼ 18 kg of enrGe. A total exposure of 21.6 kg⋅y, of enrGe was collected, and the existing claim [H. V. Klapdor-Kleingrothaus et al., Phys. Lett. B 586 (2004) 198] of 0νββ evidence was scrutinized. Gerda didn't observe any peak at Qββ or in its immediate surroundings; the limit of (90 % C.L.) is derived [Gerda collaboration: M. Agostini et al., Phys. Rev. Lett. 111, (2013) 122503]. When combining the Gerda limit with those of past HdM [HdM collaboration: H. V. Klapdor-Kleingrothaus et al., Eur. Phys. J. A12 (2001) 147] and Igex [Igex Collaboration: C. E. Aalseth et al., Phys. Rev. D 65 (2002) 092007] experiments, the lower limit of 3.0⋅1025yr (90 % C.L.) on is achieved. The background index (BI) at Qββ(∼2039keV) is ∼2.0⋅10−2cts/(keV⋅kg⋅yr) and ∼1.0⋅10−2cts/(keV⋅kg⋅yr), prior and after the pulse shape cuts respectively. Thanks to the low background the 2νββ dominates the energy spectrum below 1800 keV: the was derived on a first data set corresponding to 5.1 kg⋅yr exposure [Gerda collaboration: M. Agostini et al., J. Phys. G 40 (2013), 035110]. The ongoing experimental program, to double the exposed mass by adding new enrGe detectors with improved pulse shape discrimination features, and to implement the liquid argon scintillation light readout is outlined.