Double Beta Decay and Neutrino

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&gt；0.7X10^&lt；23&gt；years(Y)and t&gt；0.6X10^&lt；23&gt；y for the neutrinoless double beta decays(0nubetabeta)of^&lt；76&gt；Ge0^+-&gt；0^+and0^+-&gt；2^+。The former was almost same level of other results and set limit of m_&lt；nu&gt；&lt；4 eV on neutrino mass and the latter gave most stringent limit on the right-handed current.3。ELE-IV gave a lower limit of t&gt；5.4X10^&lt；18&gt；y for two neutrino double beta decay(0nubetabeta)of^&lt；100&gt；Mo.This was the most stringent limit at that time(#china_person0#).4.ELE-V gave a finite value of t-1.5X10^&lt；19&gt；y for the 2nubetabeta of^&lt；100&gt；Mo。This is the first result in the world by the counter method alone。It gives the 0 nubetabeta nuclear matrix element.It gave the most stringent lower limit of t&gt；0.6X10^&lt；22&gt；y(m_&lt；nu&gt；&lt；6 eV)for the 0nu betabeta.5.The sensitivity of the ELE-V is10^&lt；23&gt；y for a half life of0nubetabeta，corresponding to m_&lt；nu&gt；-1 eV region.6。Lower limits of t&gt；10^&lt；20&gt；-10^&lt；22&gt；y for the double strangeness exchange weak decays(*S=2)NN-&gt；H(Unddss)exclude the light H particle with the mass below2m_N(1875 MeV).7。By using0.77ton of NaI detector in ELE-V，a lower limit of t&gt；0.6X10^&lt；23&gt；y was obtained for charge nonconserving nuclear excitation.It sets upper limits of 3X10^&lt；-25&gt；and 1.5X10^&lt；-40&gt；on branching ratio of charge nonconservation mediated by the weak boson and photon.A lower lmit of 3.2X10^&lt；23&gt；y(Preliminary)on a half life of the K-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-coupled dark matter were 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.