K. Zuber, Techn. Univ. Dresden Cocoyoc, Status of double beta decay searches

Transcription

1 K. Zuber, Techn. Univ. Dresden Status of double beta decay searches

2 How to explain everything about double beta in 45 mins Cocoyoc,

3 Contents General introduction Experimental considerations GERDA COBRA SNO+ Tin Outlook and summary Apologies for not mentioning all the other experiments in greater detail

4 Double beta decay (A,Z) (A,Z+2) +2 e - + 2ν e (A,Z) (A,Z+2) + 2 e - - 2νββ 0νββ Unique process to measure the mass of the neutrino Unque process to measure character of neutrino Requires half-life measurements well beyond yrs!!!! The smaller neutrino mass the longer is half-life

5 Example - Ge76 There are only 35 candidates

6 Spectral shapes 0νββ: Peak at Q-value of nuclear transition Measured quantity: Half-life Dependencies (BG limited) T 1/2 a ε (M t/δe B) 1/2 Sum energy spectrum of both electrons link to neutrino mass 1 / T 1/2 = PS * ME 2 * (m ν / m e ) 2

7 Nuclear matrix elements talk O. Civitarese The dark side of double beta decay

8 Physical quantities Double beta decay: Effective Majorana neutrino mass Beta decay m ν = Σ U ek 2 m k m ν = U ei 2 m i = m 1 U e1 2 + m 2 U e2 2 e iα 1 + m 3U e3 2 e iα 2 m ν = U ei 2 m i = m 1 U e1 2 ± m 2 U e 2 2 ± m 3 U e 3 2 CP-invariance: Measurements are complementary ν ν ν ν ν ν = ν ν ν τ μ ν τ τ τ μ μ μ τ μ e 2 i e3 e2 e1 e 2E m U U U U U U U U U

9 The search for 0νββ or

10 Back of the envelope Τ 1/2 = ln2 a N A M t / N ββ (τ>>t) ( Background free) For half-life measurements of yrs 1 event/yr you need source atoms This is about 1000 moles of isotope, implying 100 kg Now you only can loose: nat. abundance, efficiency, background,...

11 Candidates 0νββ decay rate scales with Q 5 Isotope 2νββ decay rate scales with Q 11 Q-Value (kev) Nat. abund. (%) (PS 0v) 1 (yrs x ev 2 ) (PS 2v) 1 (yrs) Ca E E16 Ge E E18 Se E E17 Zr E E16 Mo E E17 Pd E E18 Cd E E17 Sn E E17 Te E E17 Xe E E17 Nd E E15

12 Future projects, ideas K. Zuber, Acta Polonica B 37, 1905 (2006) running as CUORICINO running asnemo-3 small scale ones will expand, very likely not a complete list...

13 Heidelberg -Moscow The detectors are decaying!! 5 isotopical enriched Ge-detectors Peak at 2039 kev

14 Heidelberg -Moscow Part of collaboration: T 1/2 = 2.23 ± 0.4 x yr m = 0.32 ± 0.03 ev H.V. Klapdor-Kleingrothaus et al., Phys. Lett. B 586, 198 (2004), Mod.Phys.Lett.A21: ,2006

15 Running experiments CUORICINO: cryogenic bolometers 40.7 kg TeO 2 DBD Q-value T m 1/2 > 3.0 x yr (90% CL) ν < ev C. Arnaboldi et al, hep-ex/ NEMO-3: TPC Future: CUORE 760 kg TeO 2 approved 10 kg enriched foils, 6 kg 100 Mo T 1/2 > 5.8 x yr (90% CL) m ν < ev A. Barabash, hep-ex/ Idea: Super-NEMO ( kg)

16 Current aims of double beta searches Check whether observed peak claimed in 76 Ge is true If yes, observe it with at least one other isotope to confirm that it is double beta decay If not, next milestone will be 50 mev suggested by oscillation results If still no observation, down to range 1-10 mev Remember: m ν ΔEB 4 Mt

17 Gran Sasso (Italy) It s all about background reduction GERDA COBRA CUORE

18 GERDA-collaboration ~90 physicists 14 institutions 6 countries

19 GERDA-Principal Setup

20 GERDA Detectors Phase II:

21 Status GERDA

22 COBRA Use large amount of CdZnTe Semiconductor Detectors Large array of CdZnTe detectors K. Zuber, Phys. Lett. B 519,1 (2001)

23 COBRA collaboration TU Dresden TU Dortmund Material Research Centre Freiburg Washington University at St. Louis University of Bratislava University of Jyvaskyla University of La Plata Czech Technical University Prague Laboratori Nazionali del Gran Sasso More welcome Supporting institutes: University of Hamburg (Germany), Jagellonian University (Poland), Los Alamos Nat. Lab. (USA)

24 Advantages Source = detector Semiconductor (Good energy resolution, clean) Room temperature Modular design (Coincidences) Two isotopes at once Industrial development of CdTe detectors 116 Cd above MeV Tracking ( Solid state TPC )

25 Background COBRA S. Pirro, Milano Beyond MeV background a priori much lower

26 Isotopes nat. ab. (%) Q (kev) Decay mode Zn ß-ß- Cd ß-ß- Cd ß-ß- Te ß-ß- Te ß-ß- Zn ß+/EC Cd ß+ß+ Cd EC/EC Te ß+/EC

27 Latest shell model calculations 116 Cd comes of best... E. Caurier et al, arxiv: , PRL 100, (2008)

28 Needed Sensitivity T 1/2 aε M t /ΔE B claim of evidence yrs yrs 50 mev yrs yrs

29 It s all about background Background from: natural radioactivity, cosmogenic produced radioisotopes, cosmic rays, neutrons Two options Energy measurement only Energy measurement and tracking 1024 pixel, pixel size: 625 μm

30 COBRA Set-up at LNGS

31 Region of interest Region of 116 Cd peak

32 New Results (selected) PRELIMINARY PRELIMINARY Decay mode (all neutrinoless) Half life (yrs) 116 Cd g.s. 8.0 x Te g.s. 3.5 x Cd g.s 1.3 x Te β + /EC g.s. 6.2 x Cd β + /EC g.s. 6.6 x Zn β + /EC g.s. 1.6 x10 18 based on 18 kg days of data, analysis ongoing

33 KING COBRA - Below 50 mev Current idea: 40x40x40 CdZnTe detectors = 420 kg, enriched in 116Cd Down to 10 mev you might be... A real time low-energy solar neutrino and Supernova experiment? e Threshold energy: 464 kev ν e 116In e 7Be contribution g.s. alone: 227 SNU 116Cd τ = 14s 116Sn K. Zuber, Phys. Lett. B 571,148 (2003) K Balasi,, T.Kosmas, P. Divari, subm.

34 The solid state TPC Semiconductor Tracker Energy resolution Tracking Massive background reduction Positive signal identification Pixelated CdZnTe detectors

35 Pixelisation Idea: Massive background reduction by particle identification α= 1 pixel, β and ββ= several connected pixel, γ= some disconnected p. 0νββ 3 MeV β α ~15μm 1-1.5mm1.5mm Beta with endpoint 3.3MeV 7.7MeV α life-time = 164.3μs

36 Option 2: Timepix TimePix CdTe Detektor 1mm Dicke, 256x256 Pixel, 55μm pitch, 1.4x1.4 cm 2 1mm Myon candidate

37 snapshot Bi alpha-beta coincidence candidate Unfortunately I can t show you a double beta event...

38 Nobody said it was going to be easy, and nobody was right George W. Bush

39

40 Test <m ν > = ev 0ν: 1000 events per year with 1% natural Nd-loaded liquid scintillator in SNO+ simulation: one year of data maximum likelihood statistical test of the shape to extract 0ν and 2ν components ~240 units of Δχ 2 significance after only 1 year!

41 β + β + -modes In general: Double charged higgs bosons, R-parity violating SUSY couplings, leptoquarks... (A,Z) (A,Z-2) + 2 e + (+2ν e ) n n p e p e β+β+ Q-4m e c 2 e - + (A,Z) (A,Z-2) + e + (+2ν e ) β+/ec 2 e - + (A,Z) (A,Z-2) (+2ν e ) EC/EC Q-2m e c 2 Q Important to reveal mechanism if 0νββ is discovered β+/ec Enhanced sensitivity to right handed weak currents (V+A)

42 Neutrino mass vs. right handed currents H int j L J + L + κj L J + R + ηj R J + L + λj R J + R EC/ß + <λ> λ,η <<1 Possible evidence <m ν >(ev) M. Hirsch et al., Z. Phys. A 347,151 (1994)

43 Double beta studies on tin Notice difference: Here source not equal to detector only X-rays and gamma rays can be observed (excited states) 124Sn: Two electron mode 112Sn: Double EC and β + /EC 1871 Q-value: 2287keV All de-excite with emission of kev gamma Q-value: 1919keV All de-excite with emission of kev gamma, more complex patterns

44 Double beta with tin Resonant enhancement (*10 6 ) of 0nu ECEC if excited state in daughter is degenerate (within 200 ev) with initial ground state. J. Dawson et al., arxiv: , Nucl. Phys. A 799, 167 (2008) Ge-Detector on surface J. Dawson et al., arxiv: , Phys. Rev. C 78, (2008) Ge-Detector underground (Felsenkeller Dredsen 125 mwe) A. Barabash, et al, arxiv: , Nucl. Phys. A 807,269 (2008) Ge - detector Underground (Modane, 4500 mwe) M. Kidd et al., Phys. Rev. C 78, (2008) Sandwich Ge-detector on surface 3 Half-life limits on excited 1871keV larger than yrs obtained, best is 9.2 x yrs (90%CL)

45 Summary Double beta decay is the gold plated channel to probe the fundamental character of neutrinos Near term experimental goals are driven by the Klapdor claim of a peak in Ge-76 To go below 50 mev requires hundreds of kilograms of enriched material, lot of ideas... Renewed interest in double EC and beta+ modes (resonance enhancement if there degenerate states? However, little information on that in the literature, Example questions: What is the signal of 0ν EC/EC? What is the positron energy spectrum in 2νβ + /EC...