T. Hachiya

Results from KamLAND-Zen

KamLAND-Zen reports on a preliminary search for neutrinoless double-beta decay with 136Xe based on 114.8 live-days after the purification of the xenon loaded liquid scintillator. In this data, the problematic 110mAg background peak identified in previous searches is reduced by more than a factor of 10. By combining the KamLAND-Zen pre- and post-purification data, we obtain a preliminary lower limit on the 0νββ decay half-life of T1/20ν>2.6×1025 yr at 90% C.L. The search sensitivity will be enhanced with additional low background data after the purification. Prospects for further improvements with future KamLAND-Zen upgrades are also presented.

Search for double-beta decay of

Abstract A search for double-beta decays of 136Xe to excited states of 136Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 0 1 + , 2 1 + and 2 2 + transitions of 0 ν β β decay were evaluated in an exposure of 89.5 kg ⋅ yr of 136Xe, while the same transitions of 2 ν β β decay were evaluated in an exposure of 61.8 kg ⋅ yr . No excess over background was found for all decay modes. The lower half-life limits of the 2 1 + state transitions of 0 ν β β and 2 ν β β decay were improved to T 1 / 2 0 ν ( 0 + → 2 1 + ) > 2.6 × 10 25 yr and T 1 / 2 2 ν ( 0 + → 2 1 + ) > 4.6 × 10 23 yr (90% C.L.), respectively. We report on the first experimental lower half-life limits for the transitions to the 0 1 + state of 136Xe for 0 ν β β and 2 ν β β decay. They are T 1 / 2 0 ν ( 0 + → 0 1 + ) > 2.4 × 10 25 yr and T 1 / 2 2 ν ( 0 + → 0 1 + ) > 8.3 × 10 23 yr (90% C.L.). The transitions to the 2 2 + states are also evaluated for the first time to be T 1 / 2 0 ν ( 0 + → 2 2 + ) > 2.6 × 10 25 yr and T 1 / 2 2 ν ( 0 + → 2 2 + ) > 9.0 × 10 23 yr (90% C.L.). These results are compared to recent theoretical predictions.

^{136}

In the late stages of nuclear burning for massive stars (

Xe to excited states of

M>8~M_{\sun}

^{136}

), the production of neutrino-antineutrino pairs through various processes becomes the dominant stellar cooling mechanism. As the star evolves, the energy of these neutrinos increases and in the days preceding the supernova a significant fraction of emitted electron anti-neutrinos exceeds the energy threshold for inverse beta decay on free hydrogen. This is the golden channel for liquid scintillator detectors because the coincidence signature allows for significant reductions in background signals. We find that the kiloton-scale liquid scintillator detector KamLAND can detect these pre-supernova neutrinos from a star with a mass of

Ba with the KamLAND-Zen experiment

25~M_{\sun}

KamLAND Sensitivity to Neutrinos from Pre-Supernova Stars

at a distance less than 690~pc with 3

A SEARCH FOR ELECTRON ANTINEUTRINOS ASSOCIATED WITH GRAVITATIONAL-WAVE EVENTS GW150914 AND GW151226 USING KAMLAND

\sigma

STUDY of ELECTRON ANTI-NEUTRINOS ASSOCIATED with GAMMA-RAY BURSTS USING KamLAND

significance before the supernova. This limit is dependent on the neutrino mass ordering and background levels. KamLAND takes data continuously and can provide a supernova alert to the community.

Search for the proton decay mode p -> ¯νK+ with KamLAND

We present a search, using KamLAND, a kiloton-scale anti-neutrino detector, for low-energy anti-neutrino events that were coincident with the gravitational-wave (GW) events GW150914 and GW151226, and the candidate event LVT151012. We find no inverse beta-decay neutrino events within ±500 s of either GW signal. This non-detection is used to constrain the electron anti-neutrino fluence and the total integrated luminosity of the astrophysical sources.