Results on Neutrinoless Double-βDecay ofGe76from Phase I of the GERDA Experiment

Abstract

Neutrinoless double beta decay is a process that violates lepton number conservation. It is predicted to occur in extensions of the standard model of particle physics. This Letter reports the results from phase I of the Germanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory (Italy) searching for neutrinoless double beta decay of the isotope (76)Ge. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kg yr. A blind analysis is performed. The background index is about 1 × 10(-2) counts/(keV kg yr) after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of (76)Ge, T(1/2)(0ν) >2.1 × 10(25) yr (90% C.L.). The combination with the results from the previous experiments with (76)Ge yields T(1/2)(0ν)>3.0 × 10(25) yr (90% C.L.).

Impact of sterile neutrinos on nuclear-assisted cLFV processes

“…In our analysis, we evaluate the contributions of the sterile states to the effective mass m ee according to [66,67]; strong bounds on the effective mass have been set by several experiments, among them GERDA [68], EXO-200 [69,70], KamLAND-ZEN [71]. In our analysis we use the most recent constraint from [70].…”

Proton decay and new contribution to 0ν2β decay in SO(10) with low-mass Z′ boson, observable n − n ¯ $$ n-\overline{n} $$ oscillation, lepton flavor violation, and rare kaon decay

“…If Pati-Salam symmetry in turn emerges from a GUT scenario like SO (10), it provides interesting possibilities of gauge coupling unification and GUT-scale representation of all charged fermion masses with the prediction of Dirac neutrino mass matrix. If one fermion singlet per generation is added to the SO(10) frame work, it has the interesting possibility of explaining light neutrino masses and mixings by experimentally verifiable gauged inverse seesaw mechanism.…”

“…In the case of 0νββ decay we analyse the existing data [7][8][9][10] on half-life or effective mass parameter using combined contributions of light and sterile neutrino exchanges in the W L − W L channel. We derive a new formula for half-life in terms of heavy sterile neutrino masses and provide line plots, band plots, and scattered plots including light neutrino masses of different hierarchies: NH, IH, Planck1, or QD type.…”

“…Experimental evidences of tiny neutrino masses compared to their charged lepton counterparts also raises the fundamental issue on the origin of these masses as well as the nature of neutrinos: whether Dirac [1] or Majorana [2]-a question whose answer rests on the detection and confirmation of 0νββ decay process on which there are a number of ongoing experiments [3][4][5][6][7][8][9][10][11]. While direct measurement of neutrino mass by KATRIN experiment is expected to probe m ν 1 ≃ 0.2 eV [12], quasi-degeneracy of neutrino masses are constrained from PLANCK satellite data on the sum of three active neutrino masses [13].…”

“…Several limitations of the SM are removed when it is embedded in a popular grand unified theory (GUT) like SO (10) which has potentialities to achieve precision unification of the three forces, accommodate tiny neutrino masses through various seesaw mechanisms [14][15][16][17][18][19][20], provide spontaneous origins of Parity and CP-violations [21][22][23][24][25], and a host of other interesting physical phenomena. Even without any additional flavor symmetry, the model succeeds in representing all fermion masses of three generations while observable baryon number violating processes are generic among its predictions of new physics beyond the SM.…”