Double Beta Decay experimental challenges Andrea Giuliani CSNSM

Double Beta Decay: experimental challenges Andrea Giuliani CSNSM Orsay, CNRS/INP 23 France

Outline Ø Introduction to Double Beta Decay Ø Challenges in front of us Ø Choice of the isotope Ø Choice of the technology Ø Status Ø Plans for the future Talks by Giorgio Gratta Kengo Nakamura Riccardo Brugnera Chiara Brofferio and posters

Decay modes for Double Beta Decay (A, Z) (A, Z+2) + 2 e- + 2 ne 2 n Double Beta Decay allowed by the Standard Model already observed – t ~1018 – 1021 y (A, Z) (A, Z+2) + 2 e- neutrinoless Double Beta Decay (0 n-DBD) never observed (except a discussed claim) t > 1025 y (A, Z) (A, Z+2) + 2 e- Double Beta Decay with Majoron (light neutral boson) never observed – t > 1022 y +c Processes and would imply new physics beyond the Standard Model violation of total lepton number conservation They are very sensitive tests to new physics since the phase space term is much larger for them than for the standard process (in particular for ) interest for 0 n-DBD lasts for 70 years ! Goeppert-Meyer proposed the standard process in 1935 Racah proposed the neutrinoless process in 1937

How many nuclei in this condition?

DBD and Majorana neutrinos A plethora of hypothetical mechanisms may induce DBD, like exchange of massive light or heavy neutrinos, right-handed W-bosons, R-parity violating , SUSY superpartners, leptoquarks…. d d 0 nbb u u Generic process inducing neutrinoless double beta decay Majorana mass term (n)R Observation of 0 n-DBD mn 0 n n n. L Schechter Valle theorem

The mass mechanism: exchange of a light virtual neutrino u d W- u ene ne e- a LH neutrino (L=1) is absorbed at this vertex a RH antineutrino (L=-1) is emitted at this vertex With massless neutrinos, the process is forbidden because neutrino has no correct helicity / lepton number to be absorbed at the second vertex Ø IF neutrinos are massive DIRAC particles: Helicities can be accommodated thanks to the finite mass, BUT Lepton number is rigorously conserved Ø IF neutrinos are massive MAJORANA particles: Helicities can be accommodated thanks to the finite mass, AND Lepton number is not relevant 0 n-DBD is forbidden 0 n-DBD is allowed

Details on the mass mechanism how 0 n-DBD is connected to neutrino mixing matrix and masses in case of process induced by light n exchange (mass mechanism) neutrinoless Double Beta Decay rate Phase space Axial vector Nuclear coupling constant matrix elements Effective Majorana mass 1/t = G(Q, Z) g. A 4 |Mnucl|2 Mbb 2 what the experimentalists try to measure parameter containing the physics: what the nuclear theorists Effective Majorana mass try to calculate Mbb = ||Ue 1 | 2 M 1 + eia | Ue 2 | 2 M 2 + eia |Ue 3 | 2 M 3 | 1 2

neutrino mass hierarchy direct inverted Mbb [e. V] Lightest neutrino mass [e. V]

Double beta decay and sterile neutrinos 3+1 model to fit reactor anomaly Mbb = ||Ue 1 | 2 M 1 + eia 1 | Ue 2 | 2 M 2 + eia 2 |Ue 3 | 2 M 3 | + eia 3 |Ue 4 | 2 M 4 | Mbbsterile Mbb light ~ 10 -2 e. V Mbbsterile | Mbb light| ≤ 4. 5 x 10 -3 e. V 95% c. l. for NH no cancellation 1. 4 x 10 -2 ≤ | Mbb light| ≤ 5 x 10 -2 e. V 95% c. l. for IH possible cancell. 5 x 10 -2 ≤ | Mbb light| 95% c. l. for QD possible cancellation Barry, Rodejohann, Zhang, JHEP 07 (2011) 091; Li, Liu, PLB 706 (2012) 406; Rodejohann, ar. Xiv: 1206. 2560

New scenarios, , , Everything is possible in IH Lower boundary in NH Vergados, Ejiri, Simkovic , Rep. Prog. Phys. 75 (2012) 106301

Three hurdles to leap over Mbb [e. V] Klapdor Krivosheina Modern Physics Letters A 21, No. 20 (2006) 1547 100 -1000 counts/y/ton Klapdor’s claim 0. 5 -5 counts/y/ton 20 me. V 0. 1 -1 counts/y/(100 ton) 1 me. V

Background demands Present generation experiments, under commissioning or construction, aim at scrutinizing Klapdor’s claim and possibly attacking the inverted hierarchy region 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 0. 1 -1 counts / y ton The order of magnitude of the target bakground is ~ 1 counts / y ton

Signal and Background sources Ø Natural radioactivity of materials (source itself, surrounding structures) 100 Mo 7. 1 x 1018 136 Xe 2. 2 x 1021 Ø Neutrons (in particular muon-induced) Ø Cosmogenic induced activity (long living) Ø 2 n Double Beta Decay d=DE/Q

The sensitivity F: lifetime corresponding to the minimum detectable number of events over background at a given confidence level b. DE MT >> 0 b: specific background coefficient [counts/(ke. V kg y)] live time source mass b. DE MT << 1 energy resolution F (MT / b. DE)1/2 F MT importance of the nuclide choice (but large uncertainty due to nuclear physics) sensitivity to b. DE 1 Mbb [G(Q, Z)]1/2 g. A 2|Mnucl| MT 1/4

Factors guiding isotope selection Magnificent Nine 1/t = G(Q, Z) g. A 4 |Mnucl|2 Mbb 2

Predicted rates Vergados, Ejiri, Simkovic , Rep. Prog. Phys. 75 (2012) 106301 Mbb =50 me. V No superisotope, but: Ø 76 Ge needs bigger efforts, 150 Nd is very interesting Ø 82 Se, 100 Mo, 116 Cd, 130 Te, 96 Zr and 136 Xe are equivalent

Isotopic abundance and enrichment

Experimental approaches Two approaches: constraints on detector materials very large masses are possible demonstrated: up to ~ 100 kg proposed: up to ~ 1000 kg e- e- Source Detector (calorimetric technique) Ø Ø scintillation phonon-mediated detection solid-state devices gaseous/lquid detectors with proper choice of the detector, very high energy resolution Ge-diodes bolometers in gaseous/liquid xenon detector, indication of event topology e- detector source e- detector Source Detector Ø Ø scintillation gaseous TPC gaseous drift chamber magnetic field and TOF it is difficult to get large source mass neat reconstruction of event topology several candidates can be studied with the same detector

Isotope, enrichment and technique End-point of 222 Rn-induced radioactivity End-point of natural g radioactivity

Isotope, enrichment and technique Excellent technologies are available in the source=detector approach: End-point of 76 Ø Ge diodes 222 Ge (GERDA, Rn-induced MAJORANA) - DE<<1% 130 Te (Te. O Ø Bolometers radioactivity 2 crystals) (CUORE) - DE<<1% Ø TPCs (EXO, NEXT), inclusion in large volume of liquid scintillator (Kam. LAND-Zen) End-point of 136 Xe natural g 130 Enrichment is “easy” and for Te radioactivity not necessary at the present level BUT Less favorable in terms of background!

Isotope, enrichment and technique End-point of 222 Rn-induced radioactivity End-point of natural g radioactivity

Isotope, enrichment and technique Almost background free isotopes! BUT End-point of 222 Rn-induced radioactivity Low isotopic abundance and problematic enrichment Better studied with source detector (tracko-calo End-point of approach) (Super. NEMO) but also natural(Nd) g in a by dissolving the element radioactivity large scintillator (SNO+) Ca. F 2 scintillators (and in principle bolometers) are interesting for 48 Ca (CANDLES)

Isotope, enrichment and technique End-point of 222 Rn-induced radioactivity End-point of natural g radioactivity

Isotope, enrichment and technique Energy region almost free from End-point of natural g background but populated 222 by degraded alphas Rn-induced radioactivity This is the realm of scintillating bolometers (Zn. Se, Zn. Mo. O 4, Cd. WO 4) (LUCIFER, LUMINEU, AMo. RE) , which offer: Ø Source=detector End-point of Ø High energy resolution - DE<<1% natural g Ø Full alpha rejection radioactivity

How healthy is the Klapdor’s evidence? Mbb [e. V] 100 -1000 counts/y/ton Klapdor’s claim It is not very healthy. . . but it is not dead!

Test Klapdor may look easy but nobody did it completely… 1990’s 2000’s Adapted from A. Faessler et al. , Phys. Rev. D 79, 053001(2009) Ge experimental range (Klapdor)

…but something new is appearing at the horizon: Xe is coming Kam. LAND-ZEN EXO Adapted from A. Faessler et al. , Phys. Rev. D 79, 053001(2009)

EXO-200 is a TPC containing 200 kg of enriched liquid xenon. The detector measures both the scintillation light and the ionization. Multi-site and single site events are separated. Zoom in the region of DBD 32 kg y Multisite events Single site events (potential signal) Background: b = 1. 5 x 10 -3 counts/(ke. V kg y) EXO coll. , PRL 109, 032505 (2012)

Kam. LAND-Zen 13 tons of liquid scintillator loaded with 300 kg of 136 Xe contained in a nylon balloon immersed in 1 kton scintillator of the Kam. LAND set-up Full spectrum Zoom in the region of DBD Kam. LAND-Zen coll. , Phys. Rev. Lett. 110: 062502, 2013

EXO+Kam. LAND-Zen and Klapdor EXO-200 T 1/20νββ > 1. 6· 1025 yr 〈Mββ〉< 140– 380 me. V (90% C. L. ) Kam. LAND-Zen T 1/20νββ > 1. 9· 1025 yr combined T 1/20νββ > 3. 4· 1025 yr 〈Mββ〉< 120– 250 me. V (90% C. L. ) Phys. Rev. Lett. 110, 062502 (2013)

76 Ge: GERDA-phase 1 Ge diodes in LAr Data taking – 18. 2 kg of isotope b ~ 2 x 10 -2 b ROI will be examined at 20 kg x y exposure (June 2013) Expected sensitivity: 1. 9 x 1025 y About ~5 counts expected for Klapdor’s central value Background: 1. 8 events in a FWHM region around Q GERDA-1 If there is a signal, the Klapdor’s affair is solved. Else, we have to wait for GERDA-2…

76 Ge: GERDA-phase 2 Instrumentation of LAr Active shielding b ~ 10 -3 b BEGe detectors pulse shape discrimination ~ 40 kg of isotopes MAJORANA demonstrator: 30 kg of enriched Ge with background target b ~ 10 -3

130 Te: CUORE 0 and CUORE 0 is running – a calibration is ongoing 11 kg of 130 Te – background target b ~ 5 x 10 -2 Klapdor’s claim Cuoricino CUORE-0 5. 9 x 1024 90% cl 2 y

130 Te: CUORE 0 and CUORE is in the assembly phase (operation end 2014) 206 kg of 130 Te – background target b ~ 1 x 10 -2 Klapdor’s claim CUORE 9. 5 x 1025 y 90% cl 5 y Cuoricino CUORE-0 5. 9 x 1024 y 90% cl 2 y

82 Se: SUPERNEMO Super. NEMO demonstrator in construction (ready at end 2014) 7 kg of 82 Se – background target b ~ 1 x 10 -4 Klapdor’s claim Full Super. NEMO 100 kg 1 x 1026 y 90% cl 5 y Super. NEMO demonstrator 6. 6 x 1024 y 90% cl 2. 5 y

Scintillating bolometers LUCIFER LUMINEU Zn. Se 82 Se ~10 kg in production Zn. Mo. O 4 100 Mo ~10 kg existing (connections with CUORE R&D and ISOTTA-ASPERA) Proof of principle largely demonstrated with ~0. 4 kg crystals Alpha/beta rejection factors much better than 99. 9% b ~ 1 x 10 -4 seems reachable: “zero” background experiments feasible at the ton x year scale Test crystals under growth

100 Mo: Scintillating bolometers As an example: Zn. Mo. O 4 single crystals enriched in 100 Mo J. W. Beeman et al, Phys. Lett. , B 710, 318 (2012) Klapdor’s claim NEMO 3 LUMINEU Pilot – 1 kg 3 x 1024 y 90% cl 3 y funded Zn. Mo. O 4 10 kg 4. 9 x 1025 y 90% cl 5 y (Cuoricino-like as a scale) ar. Xiv: 1109. 6423 v 2 [nucl-ex] 30 Nov 2011 Zn. Mo. O 4 350 kg 9. 2 x 1026 y 90% cl 5 y (CUORE-like as a scale)

Approaching and exploring the inverted hierarchy Ultimate EXO-200 (80 -200 me. V) (4 y + Rn removal) GERDA phase-2 (75 - 129 me. V) CUORE (51 – 133 me. V) Scintillating bolometers (350 kg, 5 y) (13 – 36 me. V) Initial n. EXO (EXO-200 -like 5 tons, 10 y) (10 – 30 me. V) Similar sensitivites from GERDA-3/Majorana and upgrade of Kam. LAND-Zen For speculations on the direct hierarchy, see: Batrabash, ar. Xiv: 1109. 6423 v 2 [nucl-ex] 30 Nov 2011

Looking into the crystal ball If observed Exploring QD region ~100 me. V ~8 experiments ~1 -10 kg ~ 0. 5 -1 e. V Precision measurements on ~9 isotopes Several techniques 100 kg scale If not observed Confirm on 3 -4 isotopes Ton scale If observed Explore inverted hierarchy region ~2 experiments Ton scale If not observed now 2015 2025 Explore direct hierarchy region > 10 tons Adapted from Wilkerson, Nu. Mass 2013

THE END

150 Nd: SNO+ 780 tons of liquid scintillator loaded with natural neodymium in SNO detector 44 kg – 130 kg of 150 Nd (depending on Nd fraction, between 0. 1% and 0. 3%) Data taking 2014 Crucial issue: Enrichment of Neodymium Methods alternatives to conventional room temperature centrifugation are explored. Interest for Super. NEMO too Klapdor’s claim SNO+ 1. 3 x 1025 y 90% cl 3 y