# Presentation: 491027

## Double Beta DecayWhat if we see it?

- Steve Elliott

## Outline

- Physics/Technical Goals
- Experimental Uncertainties
- NEMO/SuperNEMO
- Sean Sutton had to cancel.
- Sasha Barabash is here for discussion

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## 50 meV

**Or ~ 10****27**** yr**

**Normal**

**Inverted**

**Solar Scale**

**Atmospheric Scale**

**KKDC Claim**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## APS Study and M-180

**The APS neutrino study on the future US Neutrino Program made a few things clear. ****(****http://www.aps.org/neutrino/)**
**Double-beta decay as one of the highest priorities.**
**It recommends a staged approach beginning with 100-200 kg scaling later to 1 ton.**
**Precision measurement at degenerate scale**
**Followed by discovery potential at atmospheric scale**
**Begs the questions:**
**	****Why precision measurements?**
**	****What is required to approach the atmospheric scale?**
**	****What about the solar scale?**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Why a precision measurement?

- If <m> is near the degenerate scale:
- We will want to compare results from several isotopes to fully understand the underlying physics.
- A 10-20% decay rate measurement will allow effective comparisons between isotopes, when the matrix element uncertainty nears ~50%.

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## M2 Comparison: -1 = GM2<m>2

| Isotope | Shell Model | Rodin et al. | Civitarese & Suhonen  |
| --- | --- | --- | --- |
| 48Ca | 0.5 |  |  |
| 76Ge | 2.1 | 5.8 | 11.1 |
| 82Se | 4.5 | 4.5 | 11.8 |
| 96Zr |  | 0.1 | 12.6 |
| 100Mo |  | 1.3 | 8.8 |
| 116Cd |  | 2.0 | 14.1 |
| 128Te | 1.6 | 2.6 |  |
| 130Te | 1.2 | 2.2 | 12.2 |
| 136Xe | 0.5 | 1.0 | 21.5 |

**Differences in QRPA indicate that the two are not calculating the same thing.**
**It goes beyond the philosophy of selecting g****pp****.**
**The implementation still differs. The spread is not a measure of the uncertainty but that different groups are calculating different things.**
**There is reason to be optimistic that this will be resolved.**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Observation of (0) implies massive Majorana neutrinos, but:

**Relative rates between isotopes might discern light neutrino exchange and heavy particle exchange as the ******** mechanism.**
**Relative rates between the ground and excited states might discern light neutrino exchange and right handed current mechanisms.**
**Effective comparisons require experimental uncertainties to be small wrt theoretical uncertainties.**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Discerning ModelsKey ingredient: several isotopes, don’t use just ratios

- 0

- .25

- .25

|  | Ge | Te | Xe |
| --- | --- | --- | --- |
|  | 0.4 | 0.5 | 0.9 |
|  | 0.2 | 0.1 | 0.04 |
|  | 0.1 | 0.05 | 0.02 |
|  | 0.1 | 0.1 | 0.04 |

**C**

**R**

**S**

**SUSY**

**R**

**SUSY**

**S**

**Civitarese**
**Suhonen**
**NPA729, 867**

**Rodin et al.**
**nucl-th/**
**0503063**

**Caurier**
**NPA654, 973c**

**Faessler et al.**
**PRD58, 115004**

- M=200 meV,  =10-9

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Discerning ModelsKey ingredient: several isotopes, don’t use just ratios

- 0

- .25

- .25

- .25

- Ge

- Te

- Xe

|  | Ge | Te | Xe |
| --- | --- | --- | --- |
|  | 0.4 | 0.5 | 0.9 |
|  | 0.2 | 0.1 | 0.04 |
|  | 0.1 | 0.05 | 0.02 |
|  | 0.1 | 0.1 | 0.04 |

**C**

**R**

**S**

**SUSY**

**R**

**SUSY**

**S**

**C**

**Civitarese**
**Suhonen**
**NPA729, 867**

**Rodin et al.**
**nucl-th/**
**0503063**

**Caurier**
**NPA654, 973c**

**Faessler et al.**
**PRD58, 115004**

**.**
**.**
**.**

**A 50% uncertainty in these calculations is a good goal.**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## NuSAG Recommendations

**“****Recommendation: The Neutrino Scientific Assessment Group recommends that the highest priority for the first phase of a neutrino-less double beta decay program is to support research in two or more neutrino-less double beta decay experiments to explore the region of degenerate neutrino masses (m********  > 100 meV). The knowledge gained and the technology developed in the first phase should then be used in a second phase to extend the exploration into the inverted hierarchy region of neutrino masses (m******** > 10−20 meV) with a single experiment.”**

**Three Experiments with significant US involvement were endorsed:**
**CUORE**
**EXO**
**Majorana**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Energy Spectrum for the 2 e-

**Endpoint**
**Energy**

- Looking for a rare peak on a continuum. What background levels do we require?

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## A Recent Example

**The “feature” at 2038 keV is arguably present. This will probably require experimental testing.**
**How can a future experiment produce a convincing case? **

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Signal:Background ~ 1:1

| Half life
(years) | ~Signal
(cnts/ton-year) | ~Neutrino mass scale (meV) |
| --- | --- | --- |
| 1025 | 530 | 400 |
| 5x1026 | 10 | 100 |
| 5x1027 | 1 | 40 |
| 1029 | 0.05 | 2 |

** ****Tl and Bi in materials are the most difficult problems. **
** ****If we reach 1/t-y: Tl and Bi will be eliminated. But a “soup” of low-% contributions will remain. One must consider the large variety of neutron-induced background channels.**

**Calc. done for Ge: Ratio of M.W. required for comparison**

**To reach atmospheric scale need BG on order 1/t-y.**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Different techniques for different objectives

- Beyond a reasonable doubt: a combination of
- Correct energy
- Single-site energy deposit
- Proper detector distributions (spatial, temporal)
- Rate scales with isotope fraction
- Open and shut case: include the following
- Observe the two-electron nature of the event.
- Observe the daughter
- Observe the excited state decay
- Smoking Gun
- See the process in several isotopes

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Discovery vs. Measurementa future decision point

**These two goals may conflict. The plan forward is murky at present.**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Systematic UncertaintiesOnly recently has this become a critical issue for . 

- Live Time (Veto, various timing cuts)
-  1%
- Number of atoms (mass, enrichment, fiducial volume)
-  few %
- Analysis (gain, resolution, event selection)
-  few to maybe 10%, depending on sophistication of cuts.
- Background Model (The KDHK claim is a good test case)
-  small for this fast decay example, can dominate if background peaks have comparable strength to the  peak. Especially problematic if the peaks are unidentified.

- Statistics set the scale.
- 	1025 y; 100 kg isotope, about 400 counts/ton-year
- 	for 75% eff. 3 t-y, negligible background: ~10% result

**At the degenerate scale, 20% measurements should be feasible. Hence, comparisons will be powerful when theory is reliable to ~50%.**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Energy Spectrum

**Endpoint**
**Energy**

- Two-neutrino tail. Won’t be a problem.
- Background:Signal scales as the resolution. This is an issue.

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## (2) as a Background.Sum Energy Cut Only, Gaussian peak shape

**next generation**
**experimental**
**goal**

## Resolution: Peak Shapes

| Parameters | Shape | Fraction of (2) in ROI |
| --- | --- | --- |
| 2% resol. | Pure Gaussian | 3 x 10-9 |
| 2% resol. | B-W | 2 x 10-5 |
| 2% resol.
0.1 tail norm.
0.1 exp scale | Gauss+
Exp Tail | 4 x 10-8 |

**Shouldn’t be a problem for ~200-kg experiments, but peak shape should be understood.**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## The NEMO3 detector 

_**Source**_**: **** ****10 kg of ******** isotopes**
**     ****cylindrical, S = 20 m****2****, 60 mg/cm****2**
_**Tracking detector**_**:**** **
**    ****drift wire chamber operating **
**        ****in Geiger mode (6180 cells)**
**Gas: He + 4% ethyl alcohol + 1% Ar + 0.1% H****2****O**** **
**      **
_**Calorimeter**_**:**** **
**     ****1940 plastic scintillators**
**     ****coupled to low radioactivity PMTs **

**The NEMO3 detector**** **

**Fréjus Underground Laboratory  : 4800 m.w.e.**

**Background:** natural radioactivity, mainly 214Bi et  208Tl ( 2.6 MeV)
-                          Radon, neutrons (n,),  muons, 

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## 100Mo 22 results

- Data Phase I  Feb. 2003 –  Dec. 2004)

- 100Mo 22 results

- Cos()

- Angular Distribution

- 219 000  events
- 6914 g
- 389 days
- S/B = 40

*NEMO-3*

- 100Mo

-  E1 + E2  (keV)

- Sum Energy Spectrum

- 219 000  events
- 6914 g
- 389 days
- S/B = 40

*NEMO-3*

- 100Mo

-  factory with very high signal/bkg ratio  →  New tools for precision test
- For example: Bosonic nature of the neutrino
- (Dolgov and Smirnov, Phys. Lett. B621, 2005, 1-10)

- T1/2() = 7.11  0.02 (stat)  0.54 (syst)  1018 y

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## SuperNEMO preliminary design

- Plane and modular geometry: ~5 kg of enriched isotope per module

- Top view

- Side view

- 5 m

- 1 m

- 4 m

- 20 modules: 100 kg of enriched isotope
-              ~ 60 000 channels for drift chamber
-              ~ 20 000 PMT if scint. block
-              ~ 2 000 PMT if scint. bars

- 1 module:  Source (40 mg/cm2) 4 x 3 m2
- 	 Tracking volume: drift wire chamber in Geiger mode, ~ 3000 cells
- 	 Calorimeter: scintillators + PMTs

- 1 m

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## My Opinions: Not necessarily universally held

**Ratios of matrix element calc. are ambiguous.**
**need 3 or more measurements**
**compare absolute values along with ratios.**
**Need measurements with a total uncertainty of ~20% or less.**
**The theory groups need to define a program to demonstrate that QRPA gets “one” answer.**
**Need theory precise to about ~50%.**
**There may be “branch point” in the technological focus of experiments on the horizon: Will process be observed at degenerate scale?**
**Discovery versus investigation**

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005

## Conclusions: more generally held

- We can do it!
- The technology is ready for atmospheric scale sensitivity
- The community wants us to do it!
- Endorsed by the APS study and NuSAG
- Double beta decay experiments will have a significant impact on our understanding of the neutrino!
- Even null results will be interesting.

- Steve Elliott, Neutrino Satellite Meeting

- Oct. 29, 2005