Double beta decay and Majorana neutrinos Ettore Fiorini, Venice March 8, 2007 → → <= => Majorana =>1937 Presently an essential problem in neutrino and in astroparticle physiss

The most sensitive way to investigate the Dirac or Majorana nature of the neutrino is neutrinoless double beta decay (DBD) This very rare process was sugested in general form by Maria Goepper Mayer just one year after the Fermi theory of beta decay. Also Bruno Pontecorvo was deeply involved.

Double Beta –Disintegration M Double Beta –Disintegration M.Goeppert-Mayer, The John Hopkins University (Received May, 20 , 1935) From the Fermi theory of b- disintegration the probability of simultameous emission of two electrons (and two neutrinos) has been calculated. The result is that this process occurs sufficiently rarely to allow an half-life of over 1017 years for a nucleus, even if its isobar of atomic number different by 2 were more stable by 20 times the electron mass Double beta decay was at the beginning searched In the neutrinoless channel as a powerful way to search for lepton number non conservation. Presently it is also considered as the most powerful way to investigate the value of the mass of a Majorana neutrino

1. (A,Z) => (A,Z+2) + 2 e- + 2 ne¯ 2 1. (A,Z) => (A,Z+2) + 2 e- + 2 ne¯ 2. (A,Z) => (A,Z+2) + 2 e- + c ( …2,3 c) 3. (A,Z) => (A,Z+2) + 2 e- Process 1 has been detected in ten nuclei Process2 and 3. violate the lepton number Process 3, normally called neutrinoless DBD, would be revealed by the presence of a peak in the sum of the electron energies => <mn>≠ 0

Neutrinoless bb decay 0n - bb decay 2n - bb decay u e - d W n e - d u

1/t = G(Q,Z) |Mnucl|2 <mn>2 The rate of neutrinoless DBD strongly depends on the evaluation of the nuclear matrix elements, quite uncertain so far 1/t = G(Q,Z) |Mnucl|2 <mn>2 rate of DDB-0n Phase space Nuclear matrix elements EffectiveMajorana neutrino mass Need to search for neutrinoless DBD in various nuclei A pick could be due to some unforeseen background peak

Possible schemes for neutrino masses

New calculations by.S.Pascoli and S.T.Petkov

Experimental approaches Source = detector (calorimetric) Geochemical experiments i82Se = > 82Kr, 96Zr = > 96Mo (?) , 128Te = > 128Xe (non confirmed), 130Te = > 130Te Radiochemical experiments 238U = > 238Pu (non confirmed) e- Direct experiments Source = detector (calorimetric) Source  detector e- source detector Source  Detector

Cryogenic detectors heat bath Thermal sensor absorber crystal Incident particle absorber crystal

@ 2 MeV ~10 mk ~ 1 kg <10 eV ~ keV DE @ 5 keV ~100 mk ~ 1 mg <1 eV ~ 3 eV @ 2 MeV ~10 mk ~ 1 kg <10 eV ~ keV

Resolution of the 5x5x5 cm3 (~ 760 g ) crystals Energy [keV] Counts 210Po a line : 0.8 keV FWHM @ 46 keV 1.4 keV FWHM @ 0.351 MeV 2.1 keV FWHM @ 0.911 MeV 2.6 keV FWHM @ 2.615 MeV 3.2 keV FWHM @ 5.407 MeV (the best a spectrometer ever realized)

Present experimental situation Nucleus Experiment % Qbb Enr Technique T0n (y) <mn) 48Ca Elegant IV 0.19 4271 scintillator >1.4x1022 7-45 76Ge Heidelberg-Moscow 7.8 2039 87 ionization >1.9x1025 .12 - 1 IGEX Ionization >1.6x1025 .14 – 1.2 Klapdor et al 1.2x1025 .44 82Se NEMO 3 9.2 2995 97 tracking >1.x1023 1.8-4.9 100Mo 9.6 3034 95-99 >4.6x1023 .7-2.8 116Cd Solotvina 7.5 83 >1.7x1023 1.7 - ? 128Te Bernatovitz 34 2529 geochem >7.7  1024 .1-4 130Te Cuoricino 33.8 bolometric >2x1024 .16-.82. 136Xe DAMA 8.9 2476 69 >1.2x1024 1.1 -2.9 150Nd Irvine 5.6 3367 91 >1.2x1021 3 - ?

HM collaboration subset (KDHK): claim of evidence of 0n-DBD In December 2001, 4 authors (KDHK) of the HM collaboration announce the discovery of neutrinoless DBD t1/20n (y) = (0.8 – 18.3)  1025 y (1  1025 y b.v.) Mbb = 0.05 - 0.84 eV (95% c.l.) 54.98 kg•y 2.2 s 2001 71.7 kg•y 4 s 2004 skepticism in DBD community in 2001 better results in 2004

Two new experiments NEMO III and CUORICINO

 decay isotopes in NEMO-3 detector bb2n measurement 116Cd 405 g Qbb = 2805 keV 96Zr 9.4 g Qbb = 3350 keV 150Nd 37.0 g Qbb = 3367 keV 48Ca 7.0 g Qbb = 4272 keV 130Te 454 g Qbb = 2529 keV External bkg measurement 100Mo 6.914 kg Qbb = 3034 keV 82Se 0.932 kg Qbb = 2995 keV natTe 491 g Cu 621 g bb0n search

0n analysis 100Mo  t1/20n (y) > 4.6  1023 Mbb < 0.7 – 2.8 eV (90% c.l.) 82Se  t1/20n (y) > 1.0  1023 Mbb < 1.7 – 4.9 eV (90% c.l.)

CUORICINO

18 crystals 3x3x6 cm3 + 44 crystals 5x5x5 cm3 = 40.7 kg of TeO2 Search for the 2b|on in 130Te (Q=2529 keV) and other rare events At Hall A in the Laboratori Nazionali del Gran Sasso (LNGS) 18 crystals 3x3x6 cm3 + 44 crystals 5x5x5 cm3 = 40.7 kg of TeO2 Operation started in the beginning of 2003 => ~ 4 months Background .18±.01 c /kev/ kg/ a 2 modules, 9 detector each, crystal dimension 3x3x6 cm3 crystal mass 330 g 9 x 2 x 0.33 = 5.94 kg of TeO2 11 modules, 4 detector each, crystal dimension 5x5x5 cm3 crystal mass 790 g 4 x 11 x 0.79 = 34.76 kg of TeO2

Present CUORICINO result (new) 60Co pile-up peak 130Te DBD Q-value anticoincidence spectrum 208Tl line Energy [keV] detail DBD MT = 5.87 (kg 130Te) x y b = 0.18  0.02 c/keV/kg/y (Jul 2005) 8.35 kg year of 130Te t >3 x 1024 (90 % c.l.) <m0n> < .16 - .9 eV => Klapdor et al m0n < .1- .9 eV

DBD and Neutrino Masses Present Cuoricino region Arnaboldi et al., submitted to PRL, hep-ex/0501034 (2005). Possible evidence (best value 0.39 eV) H.V. Klapdor-Kleingrothaus et al., Nucl.Instrum.and Meth. ,522, 367 (2004). With the same matrix elements the Cuoricino limit is 0.53 eV “quasi” degeneracy m1 m2  m3 Inverse hierarchy m212= m2atm Direct hierarchy m212= m2sol Cosmological disfavoured region (WMAP) Feruglio F. , Strumia A. , Vissani F. hep-ph/0201291

Next generation experiments Name % Qbb % E B c/y T (year) Tech <m> CUORE 130Te 34 2533 90 3.5 1.8x1027 Bolometric 9-57 GERDA 76Ge 7.8 2039 3.85 2x1027 Ionization 29-94 Majorana .6 4x1027 21-67 GENIUS .4 1x1028 13-42 Supernemo 82Se 8.7 2995 1 21026 Tracking 54-167 EXO 136Xe 8.9 2476 65 .55 1.3x1028 12-31 Moon-3 100Mo 9.6 3034 85 3.8 1.7x1027 13-48 DCBA-2 150Nd 5.6 3367 80 1x1026 16-22 Candles 48Ca .19 4271 - .35 3x1027 Scintillation 29-54 CARVEL 50-94 GSO 160Gd 22 1730 200 65-? COBRA 115Cd 7.5 2805 SNOLAB+

Ionization

Ionization COBRA

C0BRA Use large amount of CdZnTe Semiconductor Detectors Array of 1cm3 CdTe detectors K. Zuber, Phys. Lett. B 519,1 (2001)

Nd dissolved in SNO => tons of material; Scintillation 0n: 1000 events per year with 1% natural Nd-loaded liquid scintillator in SNO++ by Alex Wright simulation: one year of data maximum likelihood statistical test of the shape to extract 0n and 2n components…~240 units of Dc2 significance after only 1 year!

Scintillation

Tracking SUPERNEMO

Tracking

EXO concept: scale Gotthard experiment adding Ba tagging to suppress background (136Xe136Ba+2e) single Ba detected by optical spectroscopy two options with 63% enriched Xe High pressure Xe TPC LXe TPC + scintillation calorimetry + tracking expected bkg only by -2 energy resolution E = 2% Present R&D Ba+ spectroscopy in HP Xe / Ba+ extr. energy resolution in LXe (ion.+scint.) Prototype scale: 200 kg enriched L136Xe without tagging all EXO functionality except Ba id operate in WIPP for ~two years Protorype goals: Test all technical aspects of EXO (except Ba id) Measure 2n mode Set decent limit for 0n mode (probe Heidelberg- Moscow) 2P1/2 4D3/2 2S1/2 493 nm 650 nm metastable 47s LXe TPC Full scale experiment at WIPP or SNOLAB 10 t (for LXe ⇒ 3 m3) b = 4×10-3 c/keV/ton/y 1/2  1.3×1028 y in 5 years 〈m〉  0.013 ÷ 0.037 eV

CUORE expected sensitivity disfavoured by cosmology In 5 years: Strumia A. and Vissani F. hep-ph/0503246

Other possible candidates for neutrinoless DBD Compound Isotopic abundance Transition energy 48CaF2 .0187 % keV 76Ge 7.44 " 2038.7 " 100MoPbO4 9.63 " 3034 " 116CdWO4 7.49 " 2804 " 130TeO2 34 " 2528 " 150NdF3 150NdGaO3 5.64 " “ 130Te has high transition energy and 34% isotopic abundance => enrichment non needed and/or very cheap. Any future extensions are possible Performance of CUORE, amply tested with CUORICINO

How deep should we go?

Total Muon Flux v.s. Depth Relative to Flat Overburden (cm-2 s-1) Depth (km.w.e) Relative to Flat Overburden

Neutron Flux at Underground Sites

eg. Study for 60 kg Majorana Module

CONCLUSIONS Neutrino oscillations  Dm2 ≠0  <mn> finite for at leaqst one neutrino Neutrinoless double beta decay would indicate if neutrino is a lepton violating Majorana particle and would allow in this case to determine <mn> and the hierachy of oscillations. This process has been indicated by an experiment (Klapdor) with a value of ~0.44 eV but has not yet confirmed Future experiments on neutrinoless double beta decay will allow to reach the sensitivity predicted by oscillations The multidisciplinarity of searches on double beta decay involves nuclear and e subnuclear physics, astrophysics , radioactivity, material science, geochronology etc. It could help in explaining the particle-antiparticle asymmetry of the Universe