# Presentation: 803350

## APS neutrino study midcourse meeting

**Neutrinoless** **double beta decay**
**and**** ****direct**** ****searches for**
**neutrino mass**** **

**Co-chairs: Steven Elliott and Petr Vogel**

** ****Members: Craig Aalseth, Henning Back, Loretta Dauwe,**
**  ****David Dean, Guido Drexlin, Yuri Efremenko, Hiro Ejiri,**
**  ****Jon Engel, Brian Fujikawa, Reyco Henning, Jerry Hoff-**
**  ****man, Karol Lang, Kevin Lesko, Tadafumi Kishimoto,**
**  ****Harry Miley, Rick Norman, Silvia Pascoli, Serguey**
**  ****Petcov, Andreas Piepke, Werner Roderjohann, David**
**  ****Saltzberg, Sean Sutton, Ray Warner, John Wilkerson,**
**  ****and Lincoln Wolfenstein**

## The group met at Caltech on Feb. 27-28.
We agreed on a crude outline of our
report, heard presentations from the
main experimental groups as well as
on several theoretical topics.
Writing assignment for various sections
were made and a web page (so far password
protected) was established.  

- We agreed on a crude outline of our
- report, heard presentations from the
- main experimental groups as well as
- on several theoretical topics.
- Writing assignment for various sections
- were made and a web page (so far password
- protected) was established.

## Main points of the presentation (and of the report)

-  Observation of the  decay would establish that neutrinos are massive Majorana particles. There are no loopholes.
- It would be a great supporting evidence for leptogenesis.
- The value of <m> is constrained by oscillation data.
-     Its value can distinguish between the normal and inverted hierarchies and the degenerate spectrum.
- Present experiments probe only the degenerate region. To reach the inverted one, much larger experiments are needed.
- The matrix elements are uncertain, but not a showstopper. The true uncertainty should be better understood.
- KATRIN will explore good fraction of the degenerate region. It is a well controlled laboratory experiment, complementary to the cosmological limits.

## To confirm or reject the KDHK claim of the 0 discovery,
     one needs 5-10 kmole-years exposure with low background.
This is in accord with plans of most groups. So, no change in strategy is required. It will take ~3 years to accomplish.
We will argue that R & D should be supported and funded on many fronts for the next generation of  experiments.
Eventually, two (or more) large scale experiments will be
    needed. This is because of the matrix element uncertainty
    and redundancy (exclude false positives and negatives). Also,  one will have to show that the exchange of the light Majorana neutrino is the correct mechanism.

-      one needs 5-10 kmole-years exposure with low background.
- This is in accord with plans of most groups. So, no change in strategy is required. It will take ~3 years to accomplish.
- We will argue that R & D should be supported and funded on many fronts for the next generation of  experiments.
- Eventually, two (or more) large scale experiments will be
-     needed. This is because of the matrix element uncertainty
-     and redundancy (exclude false positives and negatives). Also,  one will have to show that the exchange of the light Majorana neutrino is the correct mechanism.

## Importance of Majorana vs. Dirac(attempted for pedestrians)

- Baryons (e.g. protons and neutrons) and leptons (e.g. electrons and neutrinos) are basic constituents of matter.
- According to experience (_so far_) and the theoretical
-     description (so called Standard Model) in any reaction
-     involving elementary particles the total numbers of
-     baryons and leptons are _strictly conserved_.
- If the neutrinoless double beta decay is discovered, i.e.,
-     if neutrinos are Majorana particles, the _law of lepton_
-     _number conservation _is violated.
- That would imply that our basic ideas about the elementary
-     particles and their interactions, and more generally about
-     the whole Universe around us, must be modified.

## Discovery of 0decay would be a great supporting evidence for leptogenesis.

- There is, at present a net baryon asymmetry in the
-      Universe, B = 6x10-10. How can one explain this value?
- In the see-saw mechanism the heavy right handed
-      Majorana neutrinos NR can decay and create at temperatures near MN a net lepton asymmetry.
- This happens if CP is violated and
-      (N ’ l + H) ≠  ( N ’l + H†)
- The lepton asymmetry is trasferred at later times
-     into baryon asymmetry by the sphaleron process
-      that conserves B-L, but violates B and L.
- Existence of the heavy Majorana neutrinos
- and CP violation in their decay is thus an
- essential ingredient in the explanation of B .

## 

The value of <m> is constrained by 
   oscillation data. Its value can distinguish    between the normal and inverted 
   hierarchies and the degenerate spectrum.

- The value of <m> is constrained by
-    oscillation data. Its value can distinguish    between the normal and inverted
-    hierarchies and the degenerate spectrum.

## Blue lines: LMA I

*Blue lines: LMA I*
*(best fit only)*
*Red lines: errors*
*in oscillation *
*parameters*
*included.*

- <m> vs. the mass of the lightest neutrino

## Region 

- Region
- explored
- by KATRIN

##  cannot distinguish

-  cannot distinguish
- between `degenerate
- normal’ and `degenerate
- inverted’ while long
- baseline cannot
- distinguish between
- hierarchical  and
- degenerate.

## 
The matrix elements are uncertain, but not a showstopper. The true uncertainty should be better understood. 

- The matrix elements are uncertain, but not a showstopper. The true uncertainty should be better understood.

## From Rodin et al, PRC68,044302(2003)

- From Rodin et al, PRC_68_,044302(2003)
- Average and of 9 variants each (different potentials and

- different number
- of s.p. states.)
- The 2 most impor-
- tant parameters
- adjusted  always
- so that the gap
- and 2 decay have
- the correct value.

## From Engel & Vogel, PRC69,034304(2004)

- From Engel & Vogel, PRC_69_,034304(2004)
- Comparison of exact (full) and QRPA (dashed) m.e.

- Two shells,  apart,
- schematic force,
- but similar to the
- treatment of real
- nuclei.

## 
KATRIN will explore good fraction of the degenerate region. It is a well controlled laboratory experiment, complementary to 
   the cosmological limits.

- KATRIN will explore good fraction of the degenerate region. It is a well controlled laboratory experiment, complementary to
-    the cosmological limits.

##    Illustration of the complementarity between different 

-    Illustration of the complementarity between different
-                                             methods, for two flavors for
-                                             simplicity.

-  = sum of the masses (cosmology),
- m2 constraint from oscillations,
- Ellipses: constraints from  and
- decay.
- Upper panel: Correct choice of
- Majorana phases for  decay
- Lower panel: Incorrect choice of
- Majorana phases

- (thanks to S. Elliott)

## Limits (or values) for mi from cosmology and astrophysics

- <1.8 eV  Elgaroy et al, PRL_89_,061301(2002)
- <2.5 eV  Hannested, PRD_66_, 125011(2002)
-  <1.0 eV  Hannested, JCAP _004_, 0305(2003)
-  <0.7 eV  Spergel et al, APJ Suppl._148_,175(2003)
-  0.56+0.30-0.26 eV Allen et al., astro-ph/0306386
- These limits use similar but not identical input data.
- Large number of parameters is fitted; there are
- correlations, and typically some dependence on
- prior assumptions.
- We will argue that determining the neutrino mass in the
- lab will teach us about cosmology; it will be harder to do
- it the other way around.

## From Klapdor-Kleingrothaus,

*From Klapdor-Kleingrothaus,*
*Dietz, Krivosheina, Chkvorets,*
*hep-hp/0403018.*
*71.7 kg-y exposure,*
*spectrum without and with*
*the `0****’  line.*
*Additional  lines at 2010, 2017,*
*2022, 2053 are assigned to the*
*214**Bi decay, line at 2030,*
*previously not seen, is of an*
*unknown origin. *
*Unidentified previously fitted*
*lines at ~2066 and 2075 keV*
*are not shown now.*

- Claim by KDHK:T1/2 = 1.19-0.50+2.99 x 1025 y (3range)

## Exposure in kmole-years needed to identify the halflife

- in 1025 years labeling the curves, to 5 vs. total bckg.

*Thanks to*
*S. Elliott*

## To confirm or reject the KDHK claim of the 0 discovery, one needs 5-10 kmole-years exposure with low background.
This is in accord with plans of most groups. So, no change in strategy is required. It might take ~3 years to accomplish.
  Independently of the KDHK claim  R & D
  should be supported  and funded on many fronts for the next generation of 
decay experiments.

- This is in accord with plans of most groups. So, no change in strategy is required. It might take ~3 years to accomplish.
-   Independently of the KDHK claim  R & D
-   should be supported  and funded on many fronts for the next generation of 
- decay experiments.

## There is no shortage of ideas for the next 

- There is no shortage of ideas for the next
- generation of  decay experiments:

- The table is from Elliott & Vogel, Ann.Rev.Nuc.Part.Sci._52._
- It reflects the situation two years ago; several proposals
- have changed since, others are no longer viable.

## 
Eventually, two (or more) large scale experiments will be needed. This is 
   because of the matrix element uncertainty
   and redundancy (exclude false positives and negatives). Also,  one will have to show that the exchange of the light Majorana neutrino is the correct mechanism.

- Eventually, two (or more) large scale experiments will be needed. This is
-    because of the matrix element uncertainty
-    and redundancy (exclude false positives and negatives). Also,  one will have to show that the exchange of the light Majorana neutrino is the correct mechanism.

## Determining T1/2 in several nuclei wouldeasily distinguish between differentcalculations of matrix elements:

- Assume that 0 decay in 76Ge has T1/2= 1x1026y. What
-  halflives in 130Te and 136Xe will different calculations predict?
-                                                                    130Te                  136Xe
- Haxton & Stephenson (SM,1984)     8.8x1024              --
- Caurier et al.(SM,1996)                    3.3x1025           6.8x1025
- Engel et al.(QRPA,1988)                   5.0x1024           2.3x1025
- Staudt et al. (QRPA,1990)                2.1x1025           9.5x1025
- Rodin et al.(RQRPA,2003)                4.8x1025     (8.3-13.9)x1025
**Thus ~25% measurement in either nucleus would eliminate **
**most of the wrong entries.**