Y. Gando

Limits on Majoron-emitting double-β decays of 136Xe in the KamLAND-Zen experiment

We present limits on Majoron-emitting neutrinoless double-β decay modes based on an exposure of 112.3 days with 125 kg of 136Xe. In particular, a lower limit on the ordinary (spectral index n=1) Majoron-emitting decay half-life of 136Xe is obtained as T1/20νχ0>2.6×1024 yr at 90% C.L., a factor of five more stringent than previous limits. The corresponding upper limit on the effective Majoron-neutrino coupling, using a range of available nuclear matrix calculations, is 〈gee〉<(0.8-1.6)×10−5. This excludes a previously unconstrained region of parameter space and strongly limits the possible contribution of ordinary Majoron emission modes to 0νββ decay for neutrino masses in the inverted hierarchy scheme.

SEARCH FOR EXTRATERRESTRIAL ANTINEUTRINO SOURCES WITH THE KamLAND DETECTOR

We present the results of a search for extraterrestrial electron antineutrinos (ν_e’s)in the energy range 8.3MeV < E_(νe) < 31.8MeV using the KamLAND detector. In an exposure of 4.53 kton-year, we identify 25 candidate events. All of the candidate events can be attributed to background, most importantly neutral current atmospheric neutrino interactions, setting an upper limit on the probability of ^8B solar ν_es converting into ν_e’s at 5.3 × 10^(–5) (90% CL), if we assume an undistorted v_e shape. This limit corresponds to a solar v_e flux of 93 cm^(–2) s^(–1) or an event rate of 1.6 events (kton–year)^(–1) above the energy threshold (E_(ve) ≥ 8.3MeV). The present data also allows us to set more stringent limits on the diffuse supernova neutrino flux and on the annihilation rates for light dark matter particles.

The KamLAND Full-Volume Calibration System

We have successfully built and operated a source deployment system for the KamLAND detector. This system was used to position radioactive sources throughout the delicate 1-kton liquid scintillator volume, while meeting stringent material cleanliness, material compatibility, and safety requirements. The calibration data obtained with this device were used to fully characterize detector position and energy reconstruction biases. As a result, the uncertainty in the size of the detector fiducial volume was reduced by a factor of two. Prior to calibration with this system, the fiducial volume was the largest source of systematic uncertainty in measuring the number of antineutrinos detected by KamLAND. This paper describes the design, operation and performance of this unique calibration system.

Search for the Invisible Decay of Neutrons with KamLAND

The Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) is used in a search for single neutron or two neutron intra-nuclear disappearance that would produce holes in the

Results from KamLAND-Zen

\it{s}

Search for double-beta decay of

-shell energy level of

^{136}

^{12}

Xe to excited states of

C nuclei. Such holes could be created as a result of nucleon decay into invisible modes (

^{136}

inv

Ba with the KamLAND-Zen experiment

), e.g.