1. Experiments on Neutrino Nature and Mass
Challenges for Non-accelerator Neutrino Physics Experiments
Y. Ramachers, University of Warwick
UK HEP Forum 18/04/2008
Y. Ramachers

2. Outline How to weigh neutrinos Current Experiments: an Overview
Next-generation proposals
Summary of merits and challenges
UK HEP Forum 18/04/2008
Y. Ramachers

3. How to weigh neutrinos? Neutrino Oscillations
(see talks from yesterday: B. Kayser, Th. Schwetz, G. Ross and B. Scott)
Cosmology
(see following talk: S. King)
Direct Beta Decay Endpoint
Double Beta Decay
UK HEP Forum 18/04/2008
Y. Ramachers

4. Single and Double Beta Decay – fundamentally different playing fields
Next-generation experiment proposals (R&D, design phase, under construction)
Single Beta Decay
Double Beta Decay
KATRIN
SuperNEMO
MARE
GERDA
EXO
CUORE
MOON II
COBRA
Majorana
CANDLES
XMASS
CARVEL
SNO++
Many more …
UK HEP Forum 18/04/2008
Y. Ramachers

5. Single and Double Beta Decay – fundamentally different playing fields
Single Beta Decay:
Double Beta Decay:
UK HEP Forum 18/04/2008
Y. Ramachers

6. Single Beta Decay Two complimentary experimental approaches
Charge Spectrometer: KATRIN
Calorimeter: MARE
Source: Tritium, Q-value 18.6 keV
Filter electron energies
Count electron events above filter threshold
Energy resolution target: 0.93 eV
Mature technology: Mainz/Troitsk limit achieved 2.2 eV
Sensitivity target: 0.2 eV
Source: Rhenium-187, Q-value 2.5keV
Source = Detector: Cryogenic micro-calorimeter
Energy resolution: eV
Mature technology: TES thermometry Sensitivity target: Test Mainz/Troitsk 2.2 eV
Long-term: MARE-2, 0.2 eV
UK HEP Forum 18/04/2008
Y. Ramachers

7. Anything beyond 0.2 eV ? Motivation for new ideasdN dE 
GF2 |Mif|2
(Ee+mec2) (Q – Ee)2
F(Z,Ee)
S(Ee)
[1 + dR(Z,Ee)]
 (Q – Ee)  (Q – Ee)2 – Mn2c4
(Q – Ee)2
|ne = S Uei |nMi 
i=1 3
Q – M3
Q – M2
Q – M1
Q Ee
K(Ee) Ee
A. Giuliani, PIC2005, Prague
+ Cosmic neutrino background detection, see M. Blennow and ref. therein, astro-ph/
UK HEP Forum 18/04/2008
Y. Ramachers

8. Double Beta Decay Double Beta Decay: 2nbb Experimental signature
Allowed and observed
0nbb
Forbidden – Interesting !
Neutrinos must be massive Majorana particles
UK HEP Forum 18/04/2008
Y. Ramachers

9. Experimental Techniques
A. Nucciotti, IDM2004, Edinburgh
UK HEP Forum 18/04/2008
Y. Ramachers

10. Success and further improvements: HowTo’s
On the way to 100meV: Missing factor 2-5 gained by
fold increase in exposure (Mt) and/or
fold reduction of background, B
On the way to 10meV : Extrapolate existing experiments over
5-6 orders of magnitude !!!
Not at all hopeless, but a challenge !
UK HEP Forum 18/04/2008
Y. Ramachers

11. Irreducible background (2nbb)
HowTo 2
Electron sum energy/Q-value
Counts [a.u.]
Energy resolution
and
Irreducible background (2nbb)
Need good DE
Need good e
Need high enrichment, a
Measurement time limited
Background and Mass
count most
Choose appropriate detector technology (e, DE, a, t, cost for M) and work on B !
UK HEP Forum 18/04/2008
Y. Ramachers

12. 0nbb experiments overview
0nbb experiments overview from R. Saakyan, SLAC Exp. Seminar, Jan. 2008
0nbb experiments overview
Experiment
Isotope kg
T1/2 yr, 90% CL
mn*, meV
Start-up timescale
Status HM
76Ge 15
>
1990
finished
KDHK claim
( ) 1025 (3s)
NEMO 3
100Mo 7
(expect. 2009)
2003
running
CUORICINO
130Te 11
> (current)
2002
CUORE
210
40-92
2011
approved
GERDA, Phase I
3 1025
2009
Phase II
~31
2 1026
70-170
EXO 200
136Xe
160
2008
EXO 1t
800
2 1027
50-68
2015
R&D
SuperNEMO
82Se/150Nd
100+
(1-2) 1026
45-100
Design Study
COBRA
116Cd
151
38-96 ?
MOON II
120
26-45
* Matrix elements from MEDEX’07
or provided by experiments
UK HEP Forum 18/04/2008
Y. Ramachers

13. Heidelberg-Moscow Exp.
5 high-purity germanium detectors, enriched in 76Ge
Total active mass: kg, total exposure: 71.7 kg years
Main background from U/Th in the set-up: 0.11 c/(keV kg y) at Qbb
H.V. Klapdor-Kleingrothaus et al., NIM A522 (2004) 371
UK HEP Forum 18/04/2008
Y. Ramachers

14. Heidelberg-Moscow Exp.
Evidence peak
Full data set: 71.7 kg years
After pulse-shape analysis: 51.4 kg years
A peak at 2039 keV = Q-value for 0nbb
No counter-argument brought forward anymore: Test evidence experimentally !
UK HEP Forum 18/04/2008
Y. Ramachers

15. Comment on Gaussian peaks and low statistics
Blind-analysis reveals the subtle challenge: Efficiency without human intervention
GERDA Phase I
testing evidence claim;
13 counts on 3 bkgr
give efficiency for any(!)
Fit: 17.4%
HD-Mos. evidence:
28 counts on 10 bkgr
efficiency for Fit:
18.7%
Scan of total Signal and Background counts
D.Y. Stewart and YR, to be submitted
UK HEP Forum 18/04/2008
Y. Ramachers

16. CUORICINO Cryogenic calorimeter, TeO2 crystals
C. Arnaboldi et al., hep-ex/
Cryogenic calorimeter, TeO2 crystals
Operating Temp. about 10 mK
44 detector modules
Total mass: 40.7 kg
UK HEP Forum 18/04/2008
Y. Ramachers

17. CUORICINO F. Ferroni, ICATTP, Villa Olmo, Oct. 2007
UK HEP Forum 18/04/2008
Y. Ramachers

18. CUORICINO F. Ferroni, ICATTP, Villa Olmo, Oct. 2007
UK HEP Forum 18/04/2008
Y. Ramachers

19. NEMO-3 2nbb example event
R. Arnold et al., hep-ex/
2nbb example event
Tracking Detector: 6.9 kg 100Mo, 0.9 kg 82Se (for latest results)
(1) Source foil(s); (2) calorimeter (scintillator); (3) PMT’s; (4) tracking volume
UK HEP Forum 18/04/2008
Y. Ramachers

20. NEMO-3 results T1/2 > 5.8 × 1023 y @ 90% C.L.
R. Saakyan, SLAC Exp. Seminar,
Jan. 2008
693 days of data
Phase I + Phase II
100Mo
82Se
T1/2 > 5.8 × 1023 y @ 90% C.L.
mn < (0.8 – 1.3) eV [1-3]
T1/2 > 2.1 × 1023 y @ 90% C.L.
mn < (1.4 – 2.2) eV [1-3]
Both simple counting and likelihood methods are consistent
Data until spring 2006
UK HEP Forum 18/04/2008
Y. Ramachers

21. New Experiments: Example 1
SuperNEMO
Next-generation tracking detector
Planar geometry. 20 modules for 100+ kg
Baseline design:
Source: 40 mg/cm2;
12 m2 per module
Readout total:
~ 40-60k geiger channels
for tracking
~ 10-20k PMTs
(3k if scintillator bars design)
Single sub-module
with ~5-7 kg of isotope
R. Saakyan, SLAC Exp. Seminar,
Jan. 2008
UK HEP Forum 18/04/2008
Y. Ramachers

22. internal contaminations energy resolution (FWHM)
SuperNEMO
7 kg kg
isotope mass M
8 %
~ 30 %
isotope
100Mo
150Nd or 82Se
NEMO-3
SuperNEMO
internal contaminations
208Tl and 214Bi in the bb foil
208Tl: < 20 mBq/kg
214Bi: < 300 mBq/kg
208Tl  mBq/kg
if 82Se: 214Bi  10 mBq/kg
T1/2(bb0n) > 2 x 1024 y
<mn> < 0.3 – 0.9 eV
T1/2(bb0n) > (1-2) x 1026 y
<mn> < eV
energy resolution (FWHM)
3MeV
3 MeV
efficiency 
UK HEP Forum 18/04/2008
Y. Ramachers

23. SuperNEMO Design Study
Approved in UK, France and Spain. Smaller but vital contributions from US, Russia, Czech Republic, Japan.
Main tasks and deliverables
R&D on critical components
Calorimeter energy resolution of 4% at 3 MeV
Optimisation of tracking detector and construction (robot)
Better background rejection (e.g. extra veto counters)
Ultrapure source production and purity control
Simulations and geometry optimisation (B-field question).
Technical Design report
Experimental site selection (Frejus, Canfranc, Gran Sasso, Boulby)
UK HEP Forum 18/04/2008
Y. Ramachers

24. New Experiments: Example 2
GERDA
Next-generation semiconductor detector
70 m3 liquid Argon
Status April 2008
from report to LNGS SC:
Cryostat installed at LNGS
Phase I detectors pass stability
tests in cryogenic liquid
Phase II detector production
in preparation
Water tank construction to follow
Clean room construction in October
Kai Zuber, TU Dresden,
joined collaboration
Cryostat
6 cm copper shield
Ge Detector Array
UK HEP Forum 18/04/2008
Y. Ramachers

25. GERDA
UK HEP Forum 18/04/2008
Y. Ramachers

26. A hypothetical bb-experiment: Cherry-picking for a second UK experiment
All reviews agree on one point: There is no optimal bb-experiment!
So, pick out what is good and compromise for a practical solution:
A highly subjective procedure
M, a: e:
ΔE: B:
Large enriched source, bulk (SNO++, EXO200) or modular
Source = Detector
Germanium semiconductor energy resolution (GERDA, CUORE)
Ultra clean environment = embedded in active veto, self-shielding
(GERDA, SNO++, EXO200)
+ Tracking (SuperNEMO) for background identification + extra-physics
+ best isotope, Nd-150 (SNO++, SuperNEMO)
+ daughter isotope identification in situ (EXO)
The impossible experiment, so - compromise
UK HEP Forum 18/04/2008
Y. Ramachers

27. A hypothetical bb-experiment: Compromises
M, a: e:
ΔE: B:
Modular source
Source = Detector
Semiconductor energy resolution
Ultra clean environment = embedded in active veto, self-shielding
+ Tracking, at least coarse
+ reasonable isotope, not covered yet – Cd-116 (b-b-) or Cd-106 (b+b+)
- no daughter isotope identification
Room-temperature version of GERDA – modified COBRA:
CdZnTe semiconductors, pixel or strip-readout in liquid scintillator tank
All necessary expertise present in the UK
UK HEP Forum 18/04/2008
Y. Ramachers

28. Conclusion I Single Beta Decay can:
Measure the electron anti-neutrino mass directly, model-independent
Potentially gain access to more than one mass eigenstate and mixing matrix element
Potentially measure cosmic neutrino population
Double Beta Decay can:
Give access to the absolute mass scale
Reveal the particle nature
Evidence at 440 meV can ‘soon’ be tested independently (results maybe by )
UK HEP Forum 18/04/2008
Y. Ramachers

29. Conclusion II
The step to 100 meV sensitivity is a big step – current experiments will have to improve
The step to 10 meV is huge: All extrapolations (5-6 orders of magnitude) suffer from unknown background regime
Once upon a time: There was scope for a second UK double beta decay experiment – expertise and efforts still exist– point for discussion?
Not mentioned - beyond Mass and Nature: potentially reveal the physics mechanism for Lepton Number violation (tracking and/or matrix element measurement for many isotopes and double beta decay modes) and access CP-violation in the lepton sector together with single beta decay
UK HEP Forum 18/04/2008
Y. Ramachers