K. Zuber, Techn. Univ. Dresden Dresden, 17. Feb Double beta decay searches

Transcription

1 K. Zuber, Techn. Univ. Dresden Dresden, 17. Feb Double beta decay searches

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

3 Contents General Introduction Experimental considerations Short overview of experiments Supportive measurements for nuclear matrix elements Outlook and summary Apologies for not mentioning all the experiments in greater detail and sorry if you aren t mentioned at all...

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 the neutrino mass the longer the half-life

5 Example - Ge76 There are only 35 candidates

6 0νββ Any L=2 process can contribute to 0νββ R p violating SUSY V+A interactions Leptoquarks Double charged Higgs bosons Compositeness Heavy Majorana neutrino exchange Light Majorana neutrino exchange... 1 / T 1/2 = PS * NME 2 *ε 2

7 Schechter-Valle theorem

8 The standard lore Light Majorana neutrino exchange Measured quantity Quantity of interest Effective Majorana neutrino mass 1 / T 1/2 = PS * NME 2 * (<m ν > / m e ) 2 Phase space integral calculable Nuclear transition matrix element

9 Oscillation evidences depends on Δm 2 =m 2 2 m 1 2 No absolute mass measurement Atmospheric sin 2 2θ = 1.00, Δm 2 = ev 2 Solar + reactors sin 2 2θ = 0.81, Δm 2 = ev 2 If all three are correct... we need more (sterile ones)

10 3 Flavour oscillations (PMNS) 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 solar If sin θ 13 0 CP-violation atmospheric U= U PMNS diag(1,e iα 1,e iα 2 ) Majorana: U = cosθ 12 sinθ 12 0 sinθ 12 cosθ cosθ 13 0 sinθ 13 e iδ sinθ 13 e iδ 0 cosθ cosθ 23 sinθ 23 0 sinθ 23 cosθ e iα e iα 2 Weak eigenstates not identical to mass eigenstates, analogue to CKM mixing in quark sector

11 Neutrino mass schemes almost degenerate neutrinos m 1 m 2 m 3 hierarchical neutrino mass schemes normal inverted

12 Physical quantities 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

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

14 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)

15 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)

16 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

17 Nuclear matrix elements Most important: Short range correlations Nuclear deformation F. Simkovic et al., arxiv:

18 The search for 0νββ or

19 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,...

20 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

21 Signal information (A,Z) (A,Z+2) e - Signal: One new isotope (ionised), two electrons (fixed total energy) Single electron energies Angle between electrons Sum energy of both electrons Daughter ion (A,Z+2) Gamma rays (eg. four 511 kev photons in β + β +, excited states)

22 Experimental techniques Source = detector Source detector Semiconductors Heidelberg-Moscow, IGEX, COBRA, GERDA, MAJORANA Time projection chambers (TPC) NEMO-3, SuperNEMO, DCBA, EXO, NEXT Cryogenic bolometers CUORICINO, CUORE Scintillators SNO+, CANDLES, MOON, GSO, XMASS

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

24 SNO+ SUPERNEMO TGV CANDLES XMASS DCBA EXO MAJORANA NEXT GERDA CUORE COBRA

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

26 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

27 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

28 CUORICINO F. Bellini, NOW 2008 Statistics: kg 130 Te yrs Result: T 1/2 > 3.1 x yrs m< ev

29 CUORE Status at LNGS 19 towers 52 detectors each Start foreseen at 2012

30 NEMO Mo kg Q ββ = 3034 kev & 82 Se kg Q ββ = 2995 kev 0νββ decay search Result: T 1/2 > 5.8 x yrs Result: T 1/2 > 2.1 x yrs m< ev m< ev Based on 693 days of data, more to come soon A large number of 2nu double beta measurements

31 Super-NEMO Focus on 82 Se or 150 Nd 4 m 1 m Side view 5 m Top view 100 kg would imply 20 modules, drift chamber channels PMT channels (design dependent) Start with all modules foreseen in 2014

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

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

34 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 )

35 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

36 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

37 COBRA Set-up at LNGS

38 New Results based on 18 kg days of data, J.V. Dawson et al., submitted

39 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

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

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

42 GERDA-Principal Setup

43 Status GERDA

44 GERDA Detectors Phase II:

45 MAJORANA The demonstrator

46 60-kg of Ge detectors 30-kg of 86% enriched 76 Ge crystals required for science goal; 60-kg for background sensitivity Examine detector technology options p- and n-type, segmentation, point-contact. Low-background Cryostats & Shield ultra-clean, electroformed Cu naturally scalable Compact low-background passive Cu and Pb shield with active muon veto Agreement to locate at 4850 level at Sanford Lab Background Goal in the 0νββ peak region of interest (4 kev at 2039 kev) ~ 1 count/roi/t-y (after analysis cuts) The MAJORANA Demonstrator Module 76 Ge offers an excellent combination of capabilities & sensitivities. (Excellent energy resolution, intrinsically clean detectors, commercial technologies, best 0νββ sensitivity to date)

47 SNO+

48 Test <m ν > = ev 0ν: 1000 events per year with 1% natural Nd-loaded liquid scintillator in SNO+ Using existing SNO infrastructure Well understood detector 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!

49 CANDLES Liquid Scintillator (Veto Counter) CaF 2 (Pure) Buffer Oil Large PMT 60 CaF 2 crystals (10x10x10) cm in Lsci, total 191 kg

50 DCBA T3-Design: Y X Focus on 150 Nd, perhaps 100 Mo and 82 Se

51 XMASS 800 kg detector

52 EXO Status EXO-200 An Intermediate Prototype without Barium Tagging 200 kg enr. Xe (80% in 136 Xe) Vessel complete, welded to door Half detectors almost complete (APDs, cables under assembly) Detector at WIPP: lead shielding, Xe plumbing almost complete, cryogenics tests in progress Schedule: engineering run Summer 09 physics run Fall 09 First 2nu measurement nu 3 5 years TPC Vessel fully machined at Stanford under 7 m.w.e shielding; E-beam welding used for all but final weld to minimize introduction of radioactive background

53 Barium Tagging Single Ba+ tagging works (He, Ar) Linear Trap upgrade (S/N ratio) Work on ion transport LXe Trap In-situ tagging R+D LXe+GXe cont d EXO Full Multi-ton Xe TPC with Barium Tagging 4.4x10-3 Torr He 2 ions 1 ion

54 Supportive measurements Working packages Charge exchange reactions Precise Q-value measurements ft-values Muon capture Double electron captures Neutrino-Nucleus scattering Nucleon transfer reactions Consensus Report: K. Zuber, nucl-ex/

55 Charge exchange reactions 2νββ: Only intermediate 1 + states contribute Supportive measurementsfrom accelerators Currently: (d, 2 He) and ( 3 He,t)

56 76 Ge- 76 Se Anticorrelation in strengths (seen in most isotope pairs) Effect of deformation on 2nu matrix element seems to be a state-to-state mismatch not an overall effect. What does this imply for 0nu ME? Important is the difference in shapes between mother and daughter not absolute deformation 96 Zr and 100 Mo seem to show single state dominance D. Frekers, ECT Trento 2008 There still seems to be some classic nuclear structure physics to be done!

57 Q-values Initiated during MEDEX07

58 Q-values Isotope Using Penning traps for accurate mass measurements Q-Value (kev) Nat. abund. (%) Ca ± Ge ± 7.8 Se ± Zr ± Mo ± Pd ± Cd ± Q-Value 2009 (kev) 4274 ± ± ± ± ± ± ± 4 Sn ± ± 1.5 Te ± ± Xe ± ± 0.37 Nd ± ± ± ±0.013 F.Boehm, P. Vogel, Physics of massive neutrinos, 1992

59 Ft-values Ft-values of EC badly known, if at all! These are ground state transitions! S.K.L. Sjue et al., Phys.Rev.C 78, (2008) Extracted B(GT) of EC differs by 80% from charge exchange reaction, Disagreement with QRPA calculation (unless you allow fitting of g A with values smaller than 1)

60 Ft-values A. Faessler et al., JPG 35 (2008)

61 Double Electron capture Resonant enhancement (*10 6 ) of 0nu ECEC if excited state in daughter is degenerate (within 200 ev) with initial ground state (-> Q-values) Nuclei A,% ΔM,keV E*,keV E K E L2 74 Se ± (2 + ) Kr ± (2 + ) Ru ± (?) Cd ± (1,2 + ) Sn ± (0 + ) Ba ± (?) Ce ± (1 +,2 +) (1 +,2 +) Er ± (1 + ) A.Barabash, MEDEX 07

62 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

63 Double beta with tin 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 Dresden 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 M. Hult, K. Zuber Sandwich Ge-detector underground 3 Half-life limits on excited 1871keV larger than yrs obtained, best is 9.2 x yrs (90%CL)

64 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?) To support matrix elements a lot of supportive measurements can or should be done! The maximum of information on the 11 isotopes of interest should be obtained (ILIAS NEXT?)