Double%20beta%20decay

1
Double beta decay

• Ruben Saakyan
• UCL
• 25 March 2004

2
Outline

• Motivation
• bb status
• Situation in the UK
• Future projects and UK involvement
• Sensitivity and time scale

3
Neutrino mass. What do we
want to know?
ne
n3
n2
n1
n oscillations
0nbb only
Ue12 Ue22 Ue32
Superbeams n-factories
preferred by theorists
Mixing
inverted
normal
degenerate

• Hierarchy (n-osc and 0nbb)
• CP-violation (n-osc, 0nbb3H)
• Relative mass scale (n-osc)
• Absolute mass scale
• (0nbb3Hcosmology)

0.01 eV
0.05 eV
gt 0.1 eV
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Double beta decay
2nbb
Main candidates
48Ca,76Ge,82Se, 100Mo,136Xe,116Cd, 130Te,150Nd
0nbb
2-3 MeV

• Neutrino nature (Dirac vs Majorana)
• Absolute neutrino mass scale.
• Possible sensitivity 0.01 eV (3H 0.2 eV,
  KATRIN)
• IF degenerate hierarchy, we can measure
  everything

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The Experimental Problem( Maximize Rate/Minimize
Background)
Natural Activity t(238U, 232Th) 1010
years Target t(0nbb) gt 1024 years ? Detector Shie
lding Cryostat, or other experimental
support Front End Electronics Cosmic ray induced
activity

• Low-energy, ultralow-background eperiment.
• Overlap in experimental techniques with dark
  matter, solar ns
• UK expertise exists

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Where are we now?
ltmngt lt 0.35 0.9 eV
mscale 0.05 eV mass scale from oscillation
experi- ments
normal inverted degenerate
0.01eV 0.05eV gt0.1eV
(S. King et al.

hep-ph/0402121)
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Heidelberg-Moscow experiment claim (end 2001)
ltmngt 0.4 eV ??? 2.5-3 s
bb community immediate response Claim is at
least premature
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Heidelberg claim. Recent
developments
hep-ph/0403018. Data acquisition and analysis of
the 76Ge double beta experiment in Gran Sasso
1990-2003 accepted for publication in
NIM A

• Data reanalyzed with improved
• binning/summing
• Peak visible
• Effect reclaimed with 4.2s
• ltmgt (0.2 0.6) eV, 0.4 eV best fit
• ltmgt (0.1 0.9) eV (due to NME)

214Bi
214Bi
unknown
0nbb
Problems (my view)

• Looks more like 2.5s of effect
• Unknown peak at 2030 keV?
• 214Bi line intensities do not match

71.7 kg?yr
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Situation in the UK

• At least 4 bb experts in UK (3 academics, 1
  postdoc)
• UCL in NEMO one of two experiments currently
  taking data
• Sussex, Warwick COBRA, new approach RD
• Meeting at RAL, Sep 2003 Interest bb decay
  group gt 40 people from particle and nuclear
  communities

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Situation in the UK

• bb steering group Sacha Davidson, Brian Fulton,
  Sean Paling, Ruben Saakyan, James Stirling
  (chair), Kai Zuber
• IPPP workshop 21-23 April. Think about tackling
  NME problem
• bb strategy for UK suggested by steering group

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Where to go from here to reach
10-50 meV?A Great Number of ProposalsUK
steering group suggested roadmap
CAMEO Cd-116 1 t CdWO4 crystals
DCBA Nd-150 20 kg Nd layers between tracking chambers
SuperNEMO Se-82, Various 100 kg of Se-82(or other) foil
COBRA Te-130,Cd-116 CdTe semiconductors
CANDLES Ca-48 Several tons CaF2 crystals in liquid scint.
CUORE Te-130 750 kg TeO2 bolometers
EXO Xe-136 1 ton Xe TPC (gas or liquid)
GEM Ge-76 1 ton Ge diodes in liquid nitrogen
GENIUS Ge-76 1 ton Ge diodes in liquid nitrogen
GSO Gd-160 2 t Gd2SiO5Ce crystal scint. in liquid scint.
Majorana Ge-76 500 kg Ge diodes
MOON Mo-100 Mo sheets between plastic scint., or liq. scint.
Xe Xe-136 1.56 t of Xe in liq. Scint.
XMASS Xe-136 10 t of liquid Xe
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Future experiments expected to start in
2008/10(5 yr exposure)
Experiment, cost estimate Source and Mass Sensitivity to T1/2 (y) Sensitivity to ltmngt (eV)
Majorana 50M 76Ge, 500kg 31027 0.03 0.07
CUORE 30M 130Te, 750kg(nat) 21026 0.04 0.17
EXO 50M-100M 136Xe 1 ton 81026 0.05 0.12
SuperNEMO 30M 82Se(or other) 100 kg 21026 0.04 0.11
5 different latest NME calculations
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SuperNEMO
NEMO-III
COBRA CdTe, CdZnTe

• Criteria for choosing projects
• Competitiveness
• UK role
• Complementarity

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Suggested Future UK programmeTwo steps
SuperNEMO and COBRA

• SuperNEMO
• Quick start due to gt15 yr of RD experience
  40-50 meV by 2014, likely to be first if
  observed, disentangle mechanism of 0nbb decay
• UK one of the main proponents suggested to host
  in Boulby mine
• COBRA
• Novel approach potential for large masses
  possibility 10-20 meV by 2020-2025 possibility
  to disentangle 0nbb mechanism
• Idea of Kai Zuber (Sussex)

Highly complementary!
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Summary

• 0nbb decay is indispensable for solving neutrino
  mass puzzle
• Great interest in particle and nuclear physics
  community. Highly complimentary to existing UK
  neutrino programme
• An opportunity for UK to lead 0nbb research
• We may be not far away from the effect