Andrea Giuliani University of Insubria (Como) and INFN Milano-Bicocca Italy Searches for Neutrinoless Double Beta Decay Epiphany Conference Krakow 6 th January 2010

Outline  Neutrino mass and Double Beta Decay  Experimental challenge and strategies  Present situation  Overview of the future projects  Some very promising experimental approaches  Prospects and conclusions

Outline  Neutrino mass and Double Beta Decay  Experimental challenge and strategies  Present situation  Overview of the future projects  Some very promising experimental approaches  Prospects and conclusions

Neutrino flavor oscillations oscillations do occur neutrinos are massive  what we presently know from neutrino flavor oscillations  given the three mass eigenvalues M 1, M 2, M 3 we have approximate measurements of two  M ij 2  M 12 2 ~ (9 meV) 2 Solar  M 23 2 | ~ (50 meV) 2 Atmospheric  M ij 2  M i 2 – M j 2 )    e   approximate measurements and/or constraints on U lj  elements  of the  mixing matrix

Neutrino flavor oscillations and mass scale what we do not know from neutrino flavor oscillations: (m 1 ) 2 neutrino mass hierarchy  (m 3 ) 2 (m 2 ) 2 (m 3 ) 2 (m 1 ) 2 (  m 2 ) 13 (  m 2 ) 12 (m 2 ) 2 (  m 2 ) 23 (  m 2 ) 12 Normal hierarchy m 3 >> m 2 ~m 1 Inverted hierarchy m 2 ~m 1 >>m 3 (m 2 ) 2 (m 3 ) 2 (m 1 ) 2 Degenerate m 1 ~m 2 ~m 3 >>|m i -m j | e   absolute neutrino mass scale    DIRAC or MAJORANA nature of neutrinos   

(A,Z)  (A,Z+2) + 2e e 2 Double Beta Decay allowed by the Standard Model already observed –  y Two decay modes are usually discussed: (A,Z)  (A,Z+2) + 2e - Neutrinoless Double Beta Decay never observed (except a discussed claim)  > y 2  0  Decay modes for Double Beta Decay Neutinoless process would imply new physics beyond the Standard Model violation of lepton number conservation It is a very sensitive test to new physics since the phase space term is much larger than for the standard process interest for 0 -DBD lasts for more than 70 years ! Goeppert-Meyer proposed the standard process in 1935 Racah proposed the neutrinoless process in 1937

Double Beta Decay and neutrino physics Diagrams for the two processes discussed above: Standard process two “simultaneous” beta decays 0 -DBD a virtual neutrino is exchanged between the two electroweak lepton vertices DBD is a second order weak transition very low rates

Neutrino properties and 0 -DBD d d u u e-e- e-e- W-W- W-W- e a LH neutrino (L=1) is absorbed at this vertex e a RH antineutrino (L=-1) is emitted at this vertex in pre-oscillations standard particle physics (massless neutrinos), the process is forbidden because neutrino has not the correct helicity / lepton number to be absorbed at the second vertex  IF neutrinos are massive DIRAC particles: Helicities can be accommodated thanks to the finite mass, BUT Lepton number is rigorously conserved 0 -DBD is forbidden  IF neutrinos are massive MAJORANA particles: Helicities can be accommodated thanks to the finite mass, AND Lepton number is not relevant 0 -DBD is allowed m  0  Observation of 0 -DBD

parameter containing the physics what the nuclear theorists try to calculate what the experimentalists try to measure  = G(Q,Z) |M nucl | 2  M   2 neutrinoless Double Beta Decay rate Phase space Nuclear matrix elements Effective Majorana mass how 0 -DBD is connected to neutrino mixing matrix and masses in case of process induced by mass mechanism  M   = | |U e1 | 2 M 1 + e i   | U e2 | 2 M 2 + e i   |U e3 | 2 M 3 | < DBD and neutrino physics

S. Pascoli, S. T. Petcov and T. Schwetz, hep-ph/ From where we start… 76 Ge claim excluded by CUORICINO, NEMO3

S. Pascoli, S. T. Petcov and T. Schwetz, hep-ph/ …and where we want to go Approach the inverted hierarchy region in a first phase (  m  >50 meV) Exclude the inverted hierarchy region in a second phase (  m  >15 meV) There are techniques and experiments in preparation which have the potential to reach these sensitivities

S. Pascoli, S. T. Petcov and T. Schwetz, hep-ph/ The size of the challenge   1000 counts / y ton  1 -  10 counts / y ton   1 counts / y ton 76 Ge claim 50 meV 20 meV

Outline  Neutrino mass and Double Beta Decay  Experimental challenge and strategies  Present situation  Overview of the future projects  Some very promising experimental approaches  Prospects and conclusions

Electron sum energy spectra in DBD The shape of the two electron sum energy spectrum enables to distinguish among the two different discussed decay modes Q ~ 2-3 MeV for the most promising nuclides additional signatures:  single electron energy distribution  angular distribution sum electron energy / Q two neutrino DBD continuum with maximum at ~1/3 Q neutrinoless DBD peak enlarged only by the detector energy resolution

Background requirements To start to explore the inverted hierarchy region Sensitivity at the level of 1-10 counts / y ton To cover the inverted hierarchy region Sensitivity at the level of counts / y ton The order of magnitude of the target bakground is ~ 1 counts / y ton

Experimental strategies  Detect and identify the daughter nuclei (indirect search) geochemical experiments radiochemical experiments it is not possible to distinguish the decay channel important in the 70s-80s – no more pursued now  Detect the two electrons with a proper nuclear detector (direct search) desirable features  high energy resolution  low background  large source (many nuclides under control)  event reconstruction method a peak must be revealed over background (0 -DBD) shield cosmic rays (direct interactions and activations) underground very radio-pure materials 238 U – 232 Th   ~ y signal rate  > y present more sensitive experiments: kg future goals: ~ 1000 kg  – nuclides  reject background  study electron energy and angular distributions

Experimental approaches to direct searches Two approaches: e-e- e-e- Source  Detector (calorimetric technique)   scintillation  phonon-mediated detection  solid-state devices  gaseous detectors very large masses are possible demonstrated: up to ~ 50 kg proposed: up to ~ 1000 kg with proper choice of the detector, very high energy resolution Ge-diodes bolometers in gaseous/liquid xenon detector, indication of event topology  constraints on detector materials  in contradiction neat reconstruction of event topology  it is difficult to get large source mass several candidates can be studied with the same detector e-e- e-e- source detector Source  Detector   scintillation  gaseous TPC  gaseous drift chamber  magnetic field and TOF

Experimental sensitivity to 0 -DBD sensitivity F: lifetime corresponding to the minimum detectable number of events over background at a given confidence level importance of the nuclide choice (but large uncertainty due to nuclear physics) sensitivity to  M   (F/Q |M nucl | 2 ) 1/2  1 bEbE MT Q 1/2 1/4 |M nucl | F  (MT / b  E) 1/2 energy resolution live time source mass F  MT b  0 b = 0 b: specific background coefficient [counts/(keV kg y)]

Transition energy (MeV) 48 Ca 76 Ge 82 Se 96 Zr 100 Mo 116 Cd 130 Te 136 Xe 150 Nd Choice of the nuclide Isotopic abundance (%) 48 Ca 76 Ge 82 Se 96 Zr 100 Mo 116 Cd 130 Te 136 Xe 150 Nd Nuclear Matrix Element Sign of convergence!

C [y -1 ] 82 Se 100 Mo 116 Cd 130 Te 136 Xe 150 Nd C = |M 0 | 2 G 0 [y -1 ] 76 Ge the real figure of merit: the higher the better Predicted rate No superisotope!

Outline  Neutrino mass and Double Beta Decay  Experimental challenge and strategies  Present situation  Overview of the future projects  Some very promising experimental approaches  Prospects and conclusions

High energy resolution (<2%) No tracking capability Easy to reject 2 DBD background Low energy resolution (>2%) Tracking / topology capability Easy to approach zero backround (with the exception of 2 DBD component) e-e- e-e- Source  Detector Easy to approach the ton scale e-e- e-e- source detector Source  Detector Easy to get tracking capability Heidelberg-Moscow CUORICINO NEMO-3

The Heidelberg Moscow experiment Source = detector Well established technology of Ge diodes  Five Ge diodes for an overall mass of 10.9 kg isotopically enriched ( 86%) in 76 Ge  Underground operation in the Gran Sasso laboratory (Italy) A subset of the HD collaboration (H.V. Klapdor- Kleingrothaus et al.) in 2001 announces a discussed claim  71.7 kg year – Bkg: 0.11 counts / (kg y keV) - Signal: ± 6.87 events (Bkg:~60)  Claim: 4.2  evidence  T 1/2 = (0.69–4.18) x10 25 y (3  )  Best fit: T 1/2 = 1.19 x10 25 y (NIMA 522/PLB586)  PSA analysis (Mod. Phys. Lett. A21): ( – 0.31)x10 25 y  Tuebingen/Bari group (PRD79):  M   [eV] = 0.28 [ ] 90%CL

Significance and T 1/2 depend on Bkg model  Chkvorets, PhD dissertation Univ. HD (2008): using realistic background model peak significance reduced to 1.3 , T 1/2 = 2.2x10 25 y  Strumia & Vissani Nucl.Phys. B726 (2005) The Heidelberg Moscow experiment: criticisms The claimed peak at 2039 keV

CUORICINO Nuclide under study: 130 Te A.I.: 34%  enrichment not necessary Source = detector Bolometric technique: young (born in ~ 1985) but now firmly established Bolometric technique: the nuclear energy is measured as a temperature increase of a single crystal  T = E/C  T   V thanks to a proper thermometer, In order to get low specific heat, the temperature must be very low (5 – 10 mK) Typical signal sizes: 0.1 mK / MeV, converted to about 1 mV / MeV The sensitive part of the detector is a crystal of TeO 2

Energy absorber single TeO 2 crystal  790 g  5 x 5 x 5 cm Thermometer (doped Ge chip) Sensitive mass: 41 kg

CUORICINO results 130 Te 0  60 Co sum peak 2505 keV ~ 3 FWHM from DBD Q-value T  /2 (y) > 2.94  y (90% c.l.)  M   < 0.20 – 0.68 eV MT = 18 kg 130 Te  y Bkg = 0.18±0.02 c/keV/kg/y

NEMO3: the structure Source  detector Well established technologies in particle detection: - tracking volume with Geiger cells - plastic scintillators - magnetic field  Different sources in form of foil can be used simultaneously  Underground operation in the Frejus laboratory (France)  Water and iron shields The sources 1 SOURCE 2 TRACKING VOLUME 3 CALORIMETER detector scheme

NEMO3: the results NEMO 3 is a real  factory → seven 2  decays observed and studied Results with the strongest source ( 100 Mo) F. Mauger, TAUP2009

Present results and Klapdor’s claim

Outline  Neutrino mass and Double Beta Decay  Experimental challenge and strategies  Present situation  Overview of the future projects  Some very promising experimental approaches  Prospects and conclusions

High energy resolution (<2%) No tracking capability Easy to reject 2 DBD background Low energy resolution (>2%) Tracking / topology capability Easy to approach zero backround (with the exception of 2 DBD component) e-e- e-e- Source  Detector Easy to approach the ton scale e-e- e-e- source detector Source  Detector Easy to get tracking capability Experiments and techniques CUORE Te Array of low temperature natural TeO 2 calorimeters operated at 10 mK First step: 200 Kg (2012) – LNGS – it can take advantage from Cuoricino experience Proved energy resolution: 0.25 % FWHM GERDA - 76 Ge Array of enriched Ge diodes operated in liquid nitrogen or liquid argon First phase: 18 Kg; second phase: 40 Kg - LNGS Proved energy resolution: 0.16 % FWHM MAJORANA - 76 Ge Array of enriched Ge diodes operated in conventional Cu cryostats Based on 60 Kg modules; first step: 2x60 Kg modules Proved energy resolution: 0.16 % FWHM COBRA Cd competing candidate – 9  isotopes Array of 116 Cd enriched CdZnTe of semiconductor detectors at room temperatures Final aim: 117 kg of 116 Cd Small scale prototype at LNGS Proved energy resolution: 1.9% FWHM LUCIFER - 82 Se – 116 Cd – 100 Mo Array of scintillating bolometers operated at 10 mK (ZnSe or CdWO 4 or ZnMoO 4 ) First step: 20 Kg (2013) – LNGS – based on R&D performed by S. Pirro in LNGS Proved energy resolution: 0.25 % FWHM Even though these experiments do not have tracking capability, some space information and other tools help in reducing the background thanks to: GRANULARITY of the basic design - CUORE: 988 closed packed individual bolometers - COBRA: 64,000 closed packed individual detectors - MAJORANA: 57 closed packed individual diodes per module PULSE SHAPE DISCRIMINATION - GERDA / MAJORANA can separate single / multi site events SEGMENTATION and PIXELLIZATION Granularity can be achieved through electrodes segmentation  R&D in progress for GERDA, MAJORANA, COBRA ACTIVE SHIELDING - GERDA: Ge diodes operated in active LAr SURFACE SENSITIVITY in bolometers - R&D in progress in CUORE against energy-degraded  and  background Simultaneous LIGHT and PHONON detection in bolometers - LUCIFER Excellent  /  rejection power already demonstrated Experiments and techniques rise time distribution FAST surface events SLOW bulk events

Experiments and techniques e-e- e-e- Source  Detector Easy to approach the ton scale e-e- e-e- source detector Source  Detector Easy to get tracking capability High energy resolution (<2%) No tracking capability Easy to reject 2 DBD background Low energy resolution (>2%) Tracking / topology capability Easy to approach zero backround (with the exception of 2 DBD component) CANDLES – 48 Ca Array of natural pure (not Eu doped) CaF 2 scintillators Prove of principle completed (CANDLES I and II) Next step (CANDLES III): under commissioning 305 kg divided in 96 crystals read by 40 PMT Further step (CANDLES IV: requires R&D): 6.4 tons divided in 600 crystals: 6.4 Kg of 48 Ca Final goal (CANDLES V): 100 ton (SNO, Kamland...) Proved energy resolution: 3.4 % FWHM (extrapolated from 9.1 % at 662 keV) The good point of this search is the high Q-value of 48 Ca: 4.27 MeV  out of  (2.6 MeV end point),  (3.3 MeV end point) and  (max 2.5 MeV with quench) natural radioactivity Other background cuts come from PSD (  /  different timing) and space-time correlation for Bi-Po and Bi-Tl

Experiments and techniques e-e- e-e- Source  Detector Easy to approach the ton scale e-e- e-e- source detector Source  Detector Easy to get tracking capability High energy resolution (<2%) No tracking capability Easy to reject 2 DBD background Low energy resolution (>2%) Tracking / topology capability Easy to approach zero backround (with the exception of 2 DBD component) EXO Xe TPC of enriched liquid Xenon Event position and topology; in prospect, tagging of Ba single ion (DBD daughter)  only 2 DBD background Next step (EXO-200: funded, under commissioning): 200 kg – WIPP facility – sensitivity: meV Further steps: 1-10 ton Proved energy resolution: 3.3 % FWHM (inproved thanks to simultaneous measurement of ionization and light) In parallel with the EXO-200 development, R&D for Ba ion grabbing and tagging Ba ++ e - e - final state is identified through optical spectroscopy NEXT Xe High pressure gas TPC Total mass: 80 kg Aims at energy resolution down to 1% To be installed in CANFRANC in 2013

Experiments and techniques e-e- e-e- Source  Detector Easy to approach the ton scale e-e- e-e- source detector Source  Detector Easy to get tracking capability High energy resolution (<2%) No tracking capability Easy to reject 2 DBD background Low energy resolution (>2%) Tracking / topology capability Easy to approach zero backround (with the exception of 2 DBD component) XMASS – 136 Xe Multipurpose scintillating liquid Xe detector (Dark Matter, Double Beta Decay, solar neutrinos) Three development stages: 3 Kg (prototype)  1 ton  10 ton DBD option: low background in the MeV region  Special development with an eliptic water tank to shield high energy gamma rays High light yield and collection efficiency  energy resolution down to 1.4%  control 2 background Target: to cover inverted hierarchy with 10 ton natural or 1 ton enriched SNO+ – 150 Nd SNO detector filled with Nd-loaded liquid scintillator 0.1% loading with natural Nd → 56 Kg of isotope Very interesting and original approach. Crucial points: Nd enrichment and purity; 150 Nd nuclear matrix elements

Experiments and techniques e-e- e-e- Source  Detector Easy to approach the ton scale e-e- e-e- source detector Source  Detector Easy to get tracking capability High energy resolution (<2%) No tracking capability Easy to reject 2 DBD background Low energy resolution (>2%) Tracking capability Easy to approach zero backround (with the exception of 2 DBD component) SUPERNEMO - 82 Se or 150 Nd Modules with source foils, tracking (drift chamber in Geiger mode) and calorimetric (low Z scintillator) sections Magnetic field for charge sign Possible configuration: 20 modules with 5 kg source for each module  100 Kg in Modane extension Energy resolution: 4 % FWHM it can take advantage of NEMO3 experience MOON Mo or 82 Se or 150 Nd Multilayer plastic scintillators interleaved with source foils + tracking section (PL fibers or MWPC) MOON-1 prototype without tracking section (2006) MOON-2 prototype with tracking section Proved energy resolution: 6.8 % FWHM Final target: collect 5 y x ton DCBA - 82 Se or 150 Nd Momentum analyzer for beta particles consisting of source foils inserted in a drift chamber with magnetic field Prototype: Nd 2 O 3 foils  1.2 g of 150 Nd Space resolution ~ 0.5 mm; energy resolution 11% FWHM at 1 MeV  6 % FWHM at 3 MeV Final target: 10 modules with 84 m 2 source foil for module (126 through 330 Kg total mass) rs PM

Outline  Neutrino mass and Double Beta Decay  Experimental challenge and strategies  Present situation  Overview of the future projects  Some very promising experimental approaches  Prospects and conclusions

CUORE = closely packed array of 988 detectors 19 towers - 13 modules/tower - 4 detectors/module M = 741 kg Compact structure, ideal for active shielding From CUORICINO to CUORE ( Cryogenic Underground Observatory for Rare Events ) Each tower is a CUORICINO-like detector Special dilution refrigerator

CUORE funding and schedule  CUORE has a dedicated site in LNGS and the construction has started  The CUORE refrigerator will be commissioned in 2010  1000 crystals are funded by INFN and DoE and the delivery has started  The first CUORE tower (CUORE-0) will be assembled and operated in 2010 CUORE data taking is foreseen in 2013

CUORE sensitivity Background in 0  region (conservative estimate) 0.01 c/keV/kg/y T 1/2 0 ( 130 Te) > 2.1 x y m ββ < meV Background in 0  region (optimistic estimate) c/keV/kg/y T 1/2 0 ( 130 Te) > 6 x y m ββ < meV Surface background problem partially / fully solved Detector resolution ~ 5 keV Live time 5 years CUORE can attack the inverted hierarchy region of the neutrino mass pattern

SuperNEMO structure  kg of  isotope per module  Drift wire chamber operating in Geiger mode + plastic scintillators coupled to low radioactivity PMTs  modules for the full detector →100 – 150 kg of isotope in total  modules surrounded by water shielding  location: LSM (France) in one of the two new hall after the extension  demonstrator operational in 2011

SuperNEMO sensitivity ISOTOPE MASS (kg) ENERGY RES. (FWHM) EFFICIENCY BACKGROUND (c / keV kg y) 2  Radon 208 Tl 214 Bi NEMO3 SUPERNEMO MeV4 3 MeV 18 %30 % x x mBq/m 3 (20) 0.1 mBq/m 3 < 20  Bq/kg 2  Bq/kg < 300  Bq/kg 10  Bq/kg Improvement with respect to NEMO-3 Baseline: 82 Se T 1/2 0 ( 130 Te) > 1 – 1.5 x y m ββ < meV Other options: 150 Nd – 48 Ca → advanced enrichment technologies

CUORICINO Background  -region  -region 130 Te 76 Ge 100 Mo 116 Cd Environmental “underground” Background: 238 U and 232 Th contaminations 82 Se Scintillating bolometers: LUCIFER Q-value > 2.6 MeV + alpha tagging “zero” background

Scintillating bolometers: concepts

Scintillating bolometers: the discrimination power Scatter plot of light signals vs. heat signal Alpha light yield < beta light yieldAlpha light yield > beta light yield

Light Detector 3x3x3 CdWO 4 3x3x6 CdWO 4 Scintillating bolometers: test devices

LUCIFER structure and sensitivity Single module

Outline  Neutrino mass and Double Beta Decay  Experimental challenge and strategies  Present situation  Overview of the future projects  Some very promising experimental approaches  Prospects and conclusions

Future scenarios and branching points in terms of discovery meV meV meV sensitivity to  M  degenerate hierarchy kg isotope - 5 year scale CUORE - GERDA I / II - EXO200 - SuperNEMO - LUCIFER inverted hierarchy - atmospheric  M 2 region 1000 kg isotope - 10 year scale straightforward in some cases (enriched CUORE) GERDA phase III – EXO final – CUORE in LUCIFER mode direct hierarchy - solar  M 2 region big leap in sensitivity - new approaches required 100 tons of isotopes is the typical scale discovery if neutrino is a Majorana particle unpredictable time scale experimental situation if this range holds: - new strategies have to be developed - it is worthwhile to start to elaborate them now - next generation experiments are precious for the selection of the future approaches - a large investment in enrichment is mandatory if this range holds: - SuperNEMO could marginally see it in 82 Se or 150 Nd - SNO++ could see it in 150 Nd - GERDA phase III could see it in 76 Ge - CUORE could marginally see it in 130 Te, but could clearly detect it in 82 Se or 116 Cd if upgraded to LUCIFER-mode discovery in 3 or 4 isotopes necessary (and possible...) to confirm the observation and to improve  M   estimate if this range holds (or if 76 Ge claim is right): - GERDA phase I / II will see it in 76 Ge - SuperNEMO may investigate the mechanism ( 82 Se or 150 Nd) - LUCIFER will see it in 82 Se or 116 Cd - EXO-200 will see it in 136 Xe - SNO+ could see it in 150 Nd - CUORE will see it in 130 Te and may do multi-isotope searches simultaneously ( 130 Te Cd Mo) large scale enrichment required reduction of uncertainties in NME precision measurement era for 0 -DBD!