Double Beta Decay and Neutrino

Ultra-low background beta-ray and gamma-ray detectors ELEGANTS （ELEctron gamma-ray NeuTrino）Spectrometer) III， IV，V have been developed. By investigating double beta decays and other rare decay processconservation laws, properties （mass, properties）helicity) of neutrino and new particles have been studied.2. e - iii gave a lower limits of halflives:t>0.7X10^<23>years (y) and t> 0.6X10^<23>y for the neutrinoless double beta decays (0nubetabeta) ofGe 0^+ -> 0^+ and 0^+ -> 2^+. former was almost same level of other results and set limitof m_<nu>< 4eV on neutrino mass and the latter gave most stringent limit on the right-handedcurrent.3. e - iv gave a lower limit of t > 5.4 X 10 y for two neutrino double beta decay（0nubetabeta） of <100>Mo. This was the most stringent limit at that time (1989).4. e - v gave afinite value of t - 1.5X10^<19>y for the 2nubetabeta of ^<100>Mo. This is the first result in theworld by the counter method alone. It gives the 0nubetabeta nuclear matrix element. It gave the moststringent lower limit of t > 0.6X10^<22>y (m_<nu> < 6ev) for the 0nu betabeta.5. the sensitivity ofthe e - v is 10 y for a half life of 0nubetabeta，corresponding to m_<nu> -1eV region.6. Lower limits of t > 10^<20> - 10^<22>y for the doublestrangeness exchange weak decays (*S=2) NN->H (unddss) exclude the light H particle with the massbelow 2m_n (1875MeV).7. By using 0.77 ton of NaI detector in elev，a lower limit of t > 0.6X10 y was obtained for charge nonconserving nuclear excitation. It setsupper limits of 3x10 <-25> and 1.5X10 <-40> on branching ratio of charge nonconservation mediated bythe weak boson and photon. A lower lmit of 3.2X10 y (preliminary) on A half life of theK- electron annihilation or the violation of Pauli exclusion principle through L to K-shell8. A new这些要求最严格的charge conservation.8. A newregion of spin: coupled dark matter surveyed。

1. Ultra-low background beta-ray and gamma-ray detectors ELEGANTS (ELEctron GAmma-ray NeuTrino Spectrometer) III, IV, V have been developed. By investigating double beta decays and other rare decay process, conservation laws, properties (mass, helicity) of neutrino and new particles have been studied.2. ELE-III gave a lower limits of half lives : t>0.7X10^<23>years (y) and t > 0.6X10^<23>y for the neutrinoless double beta decays (0nubetabeta) of ^<76>Ge 0^+ -> 0^+ and 0^+ -> 2^+. The former was almost same level of other results and set limit of m_<nu>< 4eV on neutrino mass and the latter gave most stringent limit on the right-handed current.3. ELE-IV gave a lower limit of t > 5.4 X 10^<18>y for two neutrino double beta decay (0nubetabeta) of ^<100>Mo. This was the most stringent limit at that time (1989).4. ELE-V gave a finite value of tー1.5X10^<19>y for the 2nubetabeta of ^<100>Mo. This is the first result in the world by the counter method alone. It gives the 0nubetabeta nuclear matrix element. It gave the most stringent lower limit of t > 0.6X10^<22>y (m_<nu> <6eV) for the 0nu betabeta.5.The sensitivity of the ELE-V is 10^<23>y for a half life of 0nubetabeta, corresponding to m_<nu> -1eV region.6. Lower limits of t > 10^<20> - 10^<22>y for the double strangeness exchange weak decays (*S=2) NN->H (unddss) exclude the light H particle with the mass below 2m_N (1875MeV).7. By using 0.77 ton of NaI detector in ELE-V, a lower limit of t > 0.6X10^<23>y was obtained for charge nonconserving nuclear excitation. It sets upper limits of 3X10^<-25> and 1.5X10^<-40> on branching ratio of charge nonconservation mediated by the weak boson and photon. A lower lmit of 3.2X10^<23>y (preliminary) on a half life of the Kーelectron annihilation or the violation of Pauli exclusion principle through L to K-shell transition was obtained. These results were most stringent test of the charge conservation.8. A new region of spinーcoupled dark matter were surveyed.