# Presentation: 504940

## The Search for Neutrinoless Double Beta Decay

- Tashi Parsons-Moss
- BNL NCSS 2006

## β Decay and Weak Interaction

- (A, Z)  (A, Z + 1) + β- + e		(1)
- (A, Z)  (A, Z - 1) + β+ + e 		(2)
- (A, Z) + e-  (A, Z - 1) + e		(3)

## Neutrinos

- e , μ , 
- 1930 – postulated by Pauli
- 1956 – detected by Cowen *et al.*
- Oscillations and Mass

## Double Beta Decay

**(A, Z) → (A, Z + 2) + 2e****-**** + 2********	**
- (48Ca, 76Ge, 82Se, 96Zr, 100Mo, 116Cd, 128Te, 130Te, 150Nd, 238U) **	****	****	****	****	****	**
**(A, Z) → (A, Z + 2) + 2e****-****	****	****	****	****	****	****	****	**** **
**(A, Z) → (A, Z + 2) + 2e****-**** + ********0(+********0)****	****	****	****	****	****	****	**

## Possible Mechanisms of 0ββ decay 

- SUSY particles
- Leptoquarks
- Right-Handed weak interaction
- Light of Heavy Majorana Neutrinos

## 0ββ Decay and Neutrino Mass

- 3 Ranges of Mass sensitivity:
- Quasi-Degenerate ~100-500 meV
- Atmospheric neutrino oscillation results     ~20-55 meV
- Solar neutrino oscillation results     ~2-5 meV

## What’s the big deal?

-  =  ?
- Absolute mass scale for neutrinos
- Leptogenesis
- Weak Force
- Grand Unified Theories

## Challenges

- Determining the dominant mechanism
- Uncertainties in nuclear matrix elements
- Limited resources, expense
- Background, background, Background!!!
- 2ββ peak
- Cosmic radiation
- Intrinsic background
- Shielding and cryostat material

## Recent 0ββ results 

| Isotope | Exposure (kmol-y) | Background (counts) | Half-Life Limit (y) | Effective Neutrino Mass Limit (meV) |
| --- | --- | --- | --- | --- |
| 48Ca | 5 x 10-5 | 0 | > 1.4 x 1022 | < 7200-44700 |
| 76Ge | 0.467 | 21 | > 1.9 x 1025 | < 350 |
| 76Ge | 0.117 | 3.5 | > 1.6 x 1025 | < 330 - 1350 |
| 76Ge | 0.943 | 61 | = 1.2 x 1025 | = 440 |
| 82Se | 7 x 10-5 | 0 | > 2.7 x 1022
(68%) | < 5000 |
| 100Mo | 5 x 10-4 | 4 | > 5.5 x 1022 | < 2100 |
| 116Cd | 1 x 10-3 | 14 | > 1.7 x 1023 | < 1700 |
| 128Te | Geochemical | NA | > 7.7 x 1024 | < 1100-1500 |
| 130Te | 0.025 | 5 | > 5.5 x 1023 | < 370 - 1900 |
| 136Xe | 7 x 10-3 | 16 | > 4.4 x 1023 | < 1800-5200 |
| 150Nd | 6 x 10-5 | 0 | > 1.2 x 1021 | < 3000 |

## Recent claim of 0ββ detection

- Recent claim of 0ββ detection

## Heidelberg-Moscow

- 71.7 Kg-y data
- Controversial Results
- Increased interest in quasi-degenerate 76Ge experiments

## 0ββ Proposals

| Collaboration | Isotope (kmol) | Anticipated Background (counts/y) | Detector Description |
| --- | --- | --- | --- |
| CAMEO | 116Cd (2) | Few | CdWO4 crystals in liquid scintillator |
| CANDLES | 48Ca (0.04) |  | CaF2 crystals in liquid scintillator |
| COBRA | 130Te |  | CdTe semiconductors |
| CUORE | 130Te (1.4) | ≈ 60 | TeO2 bolometers |
| DCBA | 82Se (2) | ≈ 40 | Nd foils and tracking chambers |
| EXO | 136Xe (4.2) | < 1 | Xe TPC |
| GEM | 76Ge (11) | ≈ 0.8 | Ge detectors in LN |
| GENIUS | 76Ge (8.8) | ≈ 0.6 | Ge detectors in LN |
| GSO | 160Gd (1.7) |  | Gd2SiO5 crystals in liquid scintillator |
| Majorana | 76Ge (3.5) | ≈  1 | Segmented Ge detectors |
| MOON | 100Mo (2.5) | ≈  8 | Mo foils and plastic scintillator |
| MPI bare Ge | 76Ge (8.8) |  | Ge detectors in LN |
| Nano-crystals | ≈  100 kmol |  | Suspended nanoparticles |
| Super-NEMO | 82Se (0.6) | ≈ 1 | Foils with tracking |
| Xe | 136Xe (6.3) | ≈ 118 | Xe dissolved in liquid scintillator  |
| XMASS | 136Xe (6.1) |  | Liquid Xe |

## GENIUS (Germanium Nitrogen Underground Setup)

- Assumes limiting background on HM from external sources
- Array of 2.5 Kg p-type 86% enriched Ge crystals “naked” in LN2

## Majorana

- Assumes 68Ge within Ge detectors was limiting background in IGEX
- 210 86% enriched, segmented n-type Ge crystals in ultra-pure electroformed Cu cryostats

## Majorana

## MOON (Mo Observatory of Neutrinos)

- Uses unique nuclear structure of 100Mo to combine 0ββ search and solar neutrino experiment
- Modules of plastic fiber scintillators with thin layers Mo

## MOON

## Acknowledgements

- I would like to thank Richard Ferrieri and all of the TA’s, professors, students and supporters of the BNL Nuclear and Radiochemistry Summer School