We present a search for neutrinoless double-beta (0νββ) decay of 136 Xe using the full KamLAND-Zen 800 dataset with 745 kg of enriched xenon, corresponding to an exposure of 2.097 ton yr of 136 Xe. This updated search benefits from a more than twofold increase in exposure, recovery of photo-sensor gain, and reduced background from muon-induced spallation of xenon. Combining with the search in the previous KamLAND-Zen phase, we obtain a lower limit for the 0νββ decay half-life of T 0ν 1/2 > 3.8 × 10 26 yr at 90% C.L., a factor of 1.7 improvement over the previous limit. The corresponding upper limits on the effective Majorana neutrino mass are in the range 28-122 meV using phenomenological nuclear matrix element calculations.

No abstract

Neutrino interactions in low energy regions below 30 MeV, where the experimental searches for supernova relic neutrino are conducted, have a large uncertainty due to complicated nuclear effects such as the Pauli blocking effect and de-excitation of a residual nucleus. Understanding the effect of nuclear de-excitation is especially critical since neutrons measured by liquid scintillator detectors can be emitted via de-excitation. We build a systematic method to predict nuclear de-excitation associated with neutrino-carbon interaction using TALYS and Geant4. This prediction is combined with the results of neutrino event generators, and we find a large increase in neutron multiplicity.

No abstract