Phase II Upgrade of the GERDA Experiment for the Search of Neutrinoless Double Beta Decay

AbstractObservation of neutrinoless double beta decay could answer the question regarding the Majorana or Dirac nature of neutrinos. The GERDA experiment utilizes HPGe detectors enriched with the isotope 76Ge to search for this process. Recently the GERDA collaboration has unblinded data of Phase I of the experiment. In order to further improve the sensitivity of the experiment, additionally to the coaxial detectors used, 30 BEGe detectors made from germanium enriched in 76Ge will be deployed in GERDA Phase II.BEGe detectors have superior PSD capability, thus the background can be further reduced. The liquid argon surrounding the detector array will be instrumented in order to reject background by detecting scintillation light induced in the liquid argon by radiation. After a short introduction the hardware preparations for GERDA Phase II as well as the processing and characterization of the 30 BEGe detectors are discussed

Modeling of GERDA Phase II data

The GERmanium Detector Array (Gerda) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double-beta (0\u3bd\u3b2\u3b2) decay of 76Ge. The technological challenge of Gerda is to operate in a \u201cbackground-free\u201d regime in the region of interest (ROI) after analysis cuts for the full 100 kg\ub7yr target exposure of the experiment. A careful modeling and decomposition of the full-range energy spectrum is essential to predict the shape and composition of events in the ROI around Q\u3b2\u3b2 for the 0\u3bd\u3b2\u3b2 search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos (2\u3bd\u3b2\u3b2) and in order to identify the location of residual impurities. The latter will permit future experiments to build strategies in order to further lower the background and achieve even better sensitivities. In this article the background decomposition prior to analysis cuts is presented for Gerda Phase II. The background model fit yields a flat spectrum in the ROI with a background index (BI) of 16.04 120.85+0.78\ub710 123 cts/(keV\ub7kg\ub7yr) for the enriched BEGe data set and 14.68 120.52+0.47\ub710 123 cts/(keV\ub7kg\ub7yr) for the enriched coaxial data set. These values are similar to the one of Phase I despite a much larger number of detectors and hence radioactive hardware components

Limit on the Radiative Neutrinoless Double Electron Capture of 36^{36}Ar from GERDA Phase I

Neutrinoless double electron capture is a process that, if detected, would give evidence of lepton number violation and the Majorana nature of neutrinos. A search for neutrinoless double electron capture of $^{36}$Ar has been performed with germanium detectors installed in liquid argon using data from Phase I of the GERmanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory of INFN, Italy. No signal was observed and an experimental lower limit on the half-life of the radiative neutrinoless double electron capture of $^{36}$Ar was established: $T_{1/2} >$ 3.6 $\times$ 10$^{21}$ yr at 90 % C.I.Comment: 7 pages, 3 figure

Studies of Charge Accumulation In The KATRIN Main Spectrometer

Experiments in recent years have shown neutrinos have non-zero rest mass. The Karlsruhe Tritium Neutrino experiment (KATRIN) will directly probe the electron anti-neutrino mass using tritium beta decay. KATRIN's main spectrometer aims to provide a \\SI{0.2}{eV} sensitivity to the neutrino mass, an order of magnitude improvement over the previous generation of experiments. During KATRIN's most recent commissioning phase, a mono-energetic electron source was used to probe transmission properties and study associated potential systematic errors in the main spectrometer. Charge accumulation from this source is identified as a potential source for systematic error and the impact on the neutrino mass measurement is estimated.Doctor of Philosoph

Studies of Charge Accumulation In The KATRIN Main Spectrometer

Experiments in recent years have shown neutrinos have non-zero rest mass. The Karlsruhe Tritium Neutrino experiment (KATRIN) will directly probe the electron anti-neutrino mass using tritium beta decay. KATRIN's main spectrometer aims to provide a 0.2eV sensitivity to the neutrino mass, an order of magnitude improvement over the previous generation of experiments. During KATRIN's most recent commissioning phase, a mono-energetic electron source was used to probe transmission properties and study associated potential systematic errors in the main spectrometer. Charge accumulation from this source is identified as a potential source for systematic error and the impact on the neutrino mass measurement is estimated.Doctor of Philosoph

Limit on Neutrinoless Double Beta Decay of 76Ge by GERDA

The Gerda experiment at the Laboratori Nazionali del Gran Sasso in Italy uses germanium detectors made from material with an enriched Ge-76 isotope fraction to search for neutrinoless double beta decay of this nucleus. Applying a blind analysis we find no signal after an exposure of 21.6 kg.yr and a background of about 0.01 cts/(keV.kg.yr). A half-life limit of T-1/20(v) > 2.1 . 10(25) yr (90% C.L.) is extracted. The previous claim of a signal for Ge-76 is excluded with 99% probability in a model independent way