1. Neutrinoless Double Beta DecayBy
Shigeharu Kihara

2. Normal Beta Decay
(Z,A)→(Z+1,A) + e- +
Ex. n→p + e- +

3. Double Beta Decay ββ(2ν)
(Z,A) →(Z+2, A) + e- + e-+ +
Feynman Diagrams for a beta decay and double beta decay

4. Neutrinoless Double Beta decay ββ(0ν)
(Z,A) →(Z+2, A) + e1- + e2-
Criteria
ν=ύ
Mν≠0
Feynman Diagram & it’s criterion A is the mass number, Z is the nuclear charge

5. So, if we could observe ββ(0ν)…
Neutrino=antineutrino
We’ll have more to figure out about neutrinos.
Earlier neutrino oscillation experiments showed that neutrinos have a finite mass.
→ This is encouraging for the search of ββ(0ν) decay
Why interesting?

6. How can we observe ββ(0ν)
Theoretical Energy spectrum for 0v decay is different from 2v decay
Y axis.. Arbitrar. X axis= sum of kinetic energy of the two electrons…. Some work needs to be done to observe clear spectra like this… thus, try to obtain great sensitivity of <m>

7. Half-Life of ββ(0ν) G0v = two electron phase space integral
M0v=The scattering amplitude
<mv> =effective mass of neutrino
Decay rate is reciprocal of life time!
If an upper limit on rate is experimentally established, and the nuclear matrix elements are known, once can deduce the corresponding upper limit on <mv>. On the other hand, if decay is observed, one can deduce the appropriate value of <mv>

8. Calculated half-lives corresponding to <mv>=50meV
Variations in same isotopes comes from matrix elements… variations along the columns reflects the effects of both the phase space and the nuclear matrix elements.

9. Experimental Criteria
To reach <mv>~ 50meV, approximately a ton of isotope will be required.
F=isotopic abundance, x is the number of double beta decay candidate atoms per molecule, epsilon is the detector efficiency, M is the mass of isotope in kilograms, T is the live time of the experiment in years..

10. Best reported limits on T1/2 0ν

11. Gotthard Tunnel Experiment
62.5%enriched136Xe was used
Detector tracked two-electrons, indicating of double beta decay.
The energy resolution at the ββ(0ν) endpoint(2.481Mev) was ~165keV (6.6%).
The dominant background was Compton-scattered electrons from natural gamma activities.
1 example

12. Future experiments
Future experiments