Results of the search for neutrinoless double-βdecay inMo100with the NEMO-3 experiment

Abstract

The NEMO-3 detector, which had been operating in the Modane Underground Laboratory from 2003 to 2010, was designed to search for neutrinoless double-β (0νββ) decay. We report the final results of a search for 0νββ decays with 6.914 kg of 100 Mo using the entire NEMO-3 data set with a detector live time of 4.96 yr, which corresponds to an exposure of 34.3 kg · yr. We perform a detailed study of the expected background in the 0νββ signal region and find no evidence of 0νββ decays in the data. The level of observed background in the 0νββ signal region [2.8-3.2] MeV is 0.44 AE 0.13 counts=yr=kg, and no events are observed in the interval [3.2-10] MeV. We therefore derive a lower limit on the half-life of 0νββ decays in 100 Mo of * Deceased PHYSICAL REVIEW D 92, 072011 (2015) 1550-7998=2015=92 (7)=072011 (23) 072011-1 © 2015 American Physical Society T 1=2 ð0νββÞ > 1.1 × 10 24 yr at the 90% confidence level, under the hypothesis of decay kinematics similar to that for light Majorana neutrino exchange. Depending on the model used for calculating nuclear matrix elements, the limit for the effective Majorana neutrino mass lies in the range hm ν i < 0.33-0.62 eV. We also report constraints on other lepton-number violating mechanisms for 0νββ decays.

Neutrinoless double beta decay in chiral effective field theory: lepton number violation at dimension seven

“…(6.17) we factored the LEC g N N 27×1 out of M sd, 2 as to make the NME independent of the renormalization scale. With the scaling of the LECs discussed in section 4.1, the left-right operators C (9) 4,5 give the largest contribution to M ν, sd , while contributions from the purely left-handed operator C (9) 1 are suppressed by 2 χ . The dimension-six vector and axial operators C (6) VL, VR induce the additional leptonic structures in eq.…”

“…The coefficients C (6,7,9) ij are all defined to be dimensionless. Keeping the lepton flavor structure, the matching coefficients for the dimension-six operators at the electroweak scale are given by 2 …”

“…The former transforms as 5 L × 1 R while C (9) 4,5 transform as 3 L × 3 R . We will discuss their chiral representations separately below.…”

“…Finally, the NME combination M E,{L,R} and M me,{L,R} only appear for the dimension-six vector operators C Table 6. The table shows the upper limits on |m ββ | and lower limits on the scales, Λ i , related to the dimension-six, -seven, and -nine operators from the GERDA [87], NEMO [9,11], CUORE [7], and KamLAND-Zen [13] experiments, assuming…”

“…The observation of 0νββ would have far reaching implications: it would demonstrate that neutrinos are Majorana fermions [2], shed light on the mechanism of neutrino mass generation, and give insight on leptogenesis scenarios for the generation of the matterantimatter asymmetry in the universe [3]. The current experimental limits on the halflives are already impressive [4][5][6][7][8][9][10][11][12][13], at the level of T 0ν 1/2 > 5.3 × 10 25 y for 76 Ge [12] and T 0ν 1/2 > 1.07 × 10 26 y for 136 Xe [13], with next generation ton-scale experiments aiming at a sensitivity of T 0ν 1/2 ∼ 10 27−28 y. By itself, the observation of 0νββ would not immediately point to the underlying physical origin of LNV.…”