Neutrinoless Double Beta Decay. Phys 135c Spring 2007 Michael Mendenhall

Transcription

1 Neutrinoless Double Beta Decay Phys 135c Spring 2007 Michael Mendenhall

2 Theory Overview

3 neutrino Lagrangian ν c iγ 2 γ 0 ν T L ν = M D [ν R ν L + ν c LνR] c }{{} + M L [ν c Lν L + ν L νl] c + M R [ν c Rν R + ν R νr] c }{{} Dirac Majorana

4 seesaw mechanism [ ] 0 M D M D M R M R M D M L 0 λ ± = M R ± M 2 R + 4M 2 D 2 { MR M 2 D M R

5 neutrinoless double beta decays

6 neutrinoless double beta decays n e p ν e beta decay

7 neutrinoless double beta decays e e n p n p ν e n e ν e p beta decay ν e double beta decay

8 neutrinoless double beta decays n e p ν e beta decay n n e e p ν e p n n ν e e ν e p p e ν e double beta decay neutrinoless double beta decay

9 double beta decay candidates Ca 76 Ge Zr Se Mo Cd Te Te Xe Xe Nd Gd 60 64

10 decay rates

11 decay rates Γ 2ν = G 2ν M 2ν GT 2

12 decay rates Γ 2ν = G 2ν M 2ν GT 2 Γ 0ν = G 0ν M 0ν GT g2 V g 2 A M 0ν F 2 m ν 2 m ν 2

13 double beta decay rates TABLE 1 Summary of experimentally measured ββ(2ν) half-lives and matrix elements a Isotope T 2ν 1/2 (y) References M 2ν GT (MeV 1 ) 48 Ca (4.2 ± 1.2) (55, 56) Ge (1.3 ± 0.1) (57 59) Se (9.2 ± 1.0) (60, 61) Zr ( ) 1019 (62 64) Mo (8.0 ± 0.6) (65 70), (71) Cd (3.2 ± 0.3) (72 74) Te b (7.2 ± 0.3) (75, 76) Te c (2.7 ± 0.1) (75) Xe > (90% CL) (77) < Nd (68, 78) U d (2.0 ± 0.6) (79) 0.05 (Elliott & Vogel 2002)

14 neutrinoless rates TABLE 2 ββ(0ν) half-lives in units of y corresponding to m ν = 50 mev for nuclear matrix elements evaluated in the references indicated References Nucleus (20) (80) (81) (82) (24, 83) (84) 48 Ca Ge Se Mo Cd Te Xe Nd a Gd a 3.4 a deformed nucleus; deformation not taken into account. (Elliott & Vogel 2002)

15 experimental signal 2ν 0ν (Elliott & Vogel 2002)

16 experimental uncertainty Upper limit on neutrino mass m ν = ( ev) [ W fxɛg 0ν M 0ν 2 ] 1/2 1 MT no background, usual n counting statistics

17 experimental uncertainty Upper limit on neutrino mass m ν = ( ev) [ W fxɛg 0ν M 0ν 2 ] 1/2 1 MT no background, usual n counting statistics m ν = ( ev) [ W fxɛg 0ν M 0ν 2 ] 1/2 [ b E MT ] 1/4 real experiments with background

18 experimental uncertainty Upper limit on neutrino mass m ν = ( ev) [ W fxɛg 0ν M 0ν 2 ] 1/2 1 MT no background, usual n counting statistics m ν = ( ev) [ W fxɛg 0ν M 0ν 2 ] 1/2 [ b E MT ] 1/4 real experiments with background

19 lowering the limit m ν = ( ev) [ W fxɛg 0ν M 0ν 2 ] 1/2 [ b E MT ] 1/4 Good shielding Purified materials Underground lab to avoid cosmogenics Minimize excess material High energy resolution Particle tracking End product tagging

20 experimental history m 2 atm (Elliott & Vogel 2002)

21 questions?

22 Experiments

23 experimental history m 2 atm (Elliott & Vogel 2002)

24 76 32 Ge Heidelberg-Moscow 10.9 kg 86% enriched Ge best results to date

25 76 32 Ge Heidelberg-Moscow 10.9 kg 86% enriched Ge best results to date GENIUS GErmanium NItrogen Underground Setup

26 Cd Cd Zn Cd Cd Zn COBRA Cadmium-telluride 0-neutrino double-beta Research Apparatus Cd-Zn-Te detectors 400 kg as 40x40x40 1cm crystals Sensitivity up to 10 yr half life Te Te Te

27 100 Mo 82 Se NEMO Neutrino Ettore Majorana Observatory 7 kg Mo, 1kg Se in thin foils (40-60mg/cm 2 ) 6180 gas tracking drift cells 1940 cell plastic scintillator calorimeter

28 Fig. 5. The source distribution in the 20 sectors of NEMO 3. foil compositions NEMO 3 detector

29 wire chamber electron pair track

30 Te CUORE Cryogenic Underground Observatory for Rare Events 988 (5cm) 3 750g TeO2 bolometer cubes 7-10mK operating temperature by dilution refrigeration c v T 3

31 All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us? -Monty Python, Life of Brian

32 All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us? -Monty Python, Life of Brian answer: low radiation lead

33 Xe EXO Enriched Xenon Observatory prototype: 200kg Xe, to be installed at WIPP full: 10 Tons (!) enriched liquid Xe

34 Xe Easy to enrich and purify Acts as a scintillator Time Projection Chamber (TPC) configuration gives full electron tracking ion grabber No long-lived activation isotopes Possible to identify resulting Ba 136

35 questions?