Search

Cosmic-ray muons produce various radioisotopes when passing through material. These spallation products can be backgrounds for rare event searches such as in solar neutrino, double-β decay, and dark matter search experiments. The KamLAND-Zen experiment searches for neutrinoless double-β decay in 745 kg of xenon dissolved in liquid scintillator. The experiment includes dead-time-free electronics with a high efficiency for detecting muon-induced neutrons. The production yields of different radioisotopes are measured with a combination of delayed coincidence techniques, newly developed muon reconstruction, and xenon spallation identification methods. The observed xenon spallation products are consistent with results from the fluka and geant4 simulation codes.

We report a measurement of the neutrino-electron elastic scattering rate of 862 keV Be7 solar neutrinos based on a 165.4 kt d exposure of KamLAND. The observed rate is 582±94(kt d)-1, which corresponds to an 862-keV Be7 solar neutrino flux of (3.26±0.52)×109cm-2s-1, assuming a pure electron-flavor flux. Comparing this flux with the standard solar model prediction and further assuming three-flavor mixing, a νe survival probability of 0.66±0.15 is determined from the KamLAND data. Utilizing a global three-flavor oscillation analysis, we obtain a total Be7 solar neutrino flux of (5.82±1.02)×109cm-2s-1, which is consistent with the standard solar model predictions.

Neutron spin rotation is expected from quark-quark weak interactions in the standard model, which induce weak interactions among nucleons that violate parity. We present the results from an experiment searching for the effect of parity violation via the spin rotation of polarized neutrons in a liquid 4 He medium. The value for the neutron spin rotation angle per unit length in 4 He, d ϕ / d z = [ + 2.1 ± 8.3 (stat.) - 0.2 + 2.9 (sys.) ] × 10 - 7 rad/m, is consistent with zero. The result agrees with the best current theoretical estimates of the size of nucleon-nucleon weak amplitudes from other experiments and with the expectations from recent theoretical approaches to weak nucleon-nucleon interactions. In this paper we review the theoretical status of parity violation in the n → + 4 He system and discuss details of the data analysis leading to the quoted result. Analysis tools are presented that quantify systematic uncertainties in this measurement and that are expected to be essential for future measurements.