Neutrino Ettore Majorana Observatory NEMO Experiment Neutrino Ettore Majorana Observatory Xavier Sarazin 1 On behalf of the NEMO Collaboration CENBG, IN2P3-CNRS et Université de Bordeaux, France Charles University, Praha, Czech Republic CTU, Praha, Czech Republic INEEL, Idaho Falls, USA IReS, IN2P3-CNRS et Université de Strasbourg, France ITEP, Moscou, Russia JINR, Dubna, Russia Jyvaskyla University, Finland 1 LAL, IN2P3-CNRS et Université Paris-Sud, France LSCE, CNRS Gif sur Yvette, France LPC, IN2P3-CNRS et Université de Caen, France Mount Holyoke College, USA RRC Kurchatov Institute, Moscow, Russia Saga University, Saga, Japon UCL, London, Great-Britain Xavier Sarazin for the NEMO-3 Collaboration TPC Workshop 20-21 December 2004

Double beta bb(0n) decay : Physics beyond the standard model DL = 2 Process Majorana Neutrino n = n and effective mass <mn> Right-handed current in weak interaction Majoron emission SUSY particle exchange bb(0n) : 2n  2p+2e- p n W- e- neR h nM neL h ( ) e- W- n p (Qbb ~ MeV)

Philosophy of NEMO experiment Use a Tracking Detector + a Magnetic Field in order to recognize e-, e+, g and a particles Zero-background experiment Gold-event experiment with a direct signature of the two emitted e-

Fréjus Underground Laboratory : 4800 m.w.e. The NEMO3 detector 3 m 4 m B (25 G) 20 sectors Fréjus Underground Laboratory : 4800 m.w.e. Magnetic field: 25 Gauss Gamma shield: Pure Iron (e = 18 cm) Neutron shield: 30 cm water + Boron (ext. wall); 40 cm wood (top and bottom) Source: 10 kg of  isotopes cylindrical, S = 20 m2, e ~ 60 mg/cm2 Tracking detector: drift wire chamber operating in Geiger mode (6180 cells) Gas: He + 4% ethyl alcohol + 1% Ar + 0.1% H2O Calorimeter: FWHM ~ 15% @ 1 MeV 1940 plastic scintillators coupled to low radioactivity PMTs ToF resolution 250 ps @ 1 MeV Able to identify e-, e+, g and a

PMTs scintillators Cathodic rings Wire chamber Calibration tube bb isotope foils

AUGUST 2001

Start taking data 14 February 2003 NEMO-3 Opening Day, July 2002 Start taking data 14 February 2003 Water tank wood coil Iron shield

bb 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 (All the enriched isotopes produced in Russia)

bb events selection in NEMO-3 Deposited energy: E1+E2= 2088 keV Internal hypothesis: (Dt)mes –(Dt)theo = 0.22 ns Common vertex: (Dvertex) = 2.1 mm Vertex emission (Dvertex)// = 5.7 mm Transverse view Longitudinal view Run Number: 2040 Event Number: 9732 Date: 2003-03-20 Criteria to select bb events: 2 tracks with charge < 0 2 PMT, each > 200 keV PMT-Track association Common vertex Internal hypothesis (external event rejection) No other isolated PMT (g rejection) No delayed track (214Bi rejection) bb events selection in NEMO-3 Typical bb2n event observed from 100Mo Transverse view Run Number: 2040 Event Number: 9732 Date: 2003-03-20 Longitudinal view 100Mo foil 100Mo foil Geiger plasma longitudinal propagation Drift distance Scintillator + PMT Trigger: 1 PMT > 150 keV 3 Geiger hits (2 neighbour layers + 1) Trigger rate = 7 Hz bb events: 1 event every 1.5 minutes

100Mo 22 preliminary results Neutrino 2004 100Mo 22 preliminary results (Data 14 Feb. 2003 – 22 Mar. 2004) Sum Energy Spectrum Angular Distribution NEMO-3 145 245 events 6914 g 241.5 days S/B = 45.8 NEMO-3 145 245 events 6914 g 241.5 days S/B = 45.8 100Mo 100Mo Data 22 Monte Carlo Data Background subtracted 22 Monte Carlo Background subtracted E1 + E2 (keV) Cos() T1/2 = 7.72 ± 0.02 (stat) ± 0.54 (syst)  1018 y 4.57 kg.y

NEMO can measure each component of background Radon Internal 214Bi impurities (e-, delayed a) channel with T1/2 (a) = 164 ms (214Bi - 214Po -210Pb ) Internal 208Tl impurities Internal (e- N g) channel with Eg= 2.6 MeV (e-, delayed a) channel with T1/2(a)=300 ns (212Bi  212Po) External 208Tl impurities External (e-, g) channel External neutrons External gammas e- crossing, e+e-, e-e- > 4 MeV

BACKGROUND EVENTS OBSERVED BY NEMO-3… Electron crossing > 4 MeV Neutron capture Electron + a delay track (164 ms) 214Bi  214Po  210Pb  Electron + N g’s 208Tl (Eg = 2.6 MeV) Electron – positron pair B rejection

Radon was the dominant background Radon in the NEMO-3 gas of the wire chamber Due to a tiny diffusion of the radon of the laboratory inside the detector A(Radon) in the lab ~15 Bq/m3 Two independant measurements of radon in NEMO-3 gas Good agreement between the two measurements Radon detector at the input/output of the NEMO-3 gas ~ 20 counts/day for 20 mBq/ m3 (1e- + 1 a) channel in the NEMO-3 data: Delayed tracks (<700 ms) to tag delayed a from 214Po 214Bi  214Po (164 ms)  210Pb ~ 200 counts/hour for 20 mBq/m3 A(Radon) in NEMO-3  20 mBq/m3 Decay in gas b- delayed a 222Rn (3.8 days) 218Po 214Pb 214Bi 214Po 210Pb b a 164 ms ~ 1 bb0n-like events/year/kg with 2.8 < E1+E2 < 3.2 MeV Radon was the dominant background for bb0n search in NEMO-3 !!!

bb0n Analysis with 100Mo T1/2(bb0n) > 3.5 1023 y 90% C.L. Neutrino 2004 100Mo 6914 g 265 days Data bb2n Monte-Carlo Radon E1+E2 (MeV) bb0n arbitrary unit Cu + natTe + 130Te 265 days Radon Monte-Carlo Data E1+E2 (MeV) 8 11.4  3.4 ____ 2.6  0.7 2 2.6<E1+E2<3.2 2.8<E1+E2<3.2 100Mo 2.6<E1+E2<3.2 2.8<E1+E2<3.2 100Mo 2b2n M-C 32.3  1.9 1.4  0.2 Radon M-C 23.5  6.7 5.6  1.7 TOTAL Monte-Carlo 55.8  7.0 7.0  1.7 DATA 50 8 T1/2(bb0n) > 3.5 1023 y 90% C.L. mn < 0.7 – 1.2 eV

Free-Radon Purification System in construction Radon was the dominant background for NEMO-3 A(222Rn) in the LSM ~ 15 Bq/m3 Factor ~ 10 too high May 2004 : Tent surrounding the detector May 2004 October 2004 : Radon-free SuperKamiokande-like Air Factory A(222Rn) < 10 mBq/m3 120 m3/h 2 x 500 kg charcoal @ -40oC Today A(222Rn) in tent < 0.5 Bq/m3 Rejection Factor > 30

Expected sensitivity after 5 years of data Conclusions after more than 1 year of NEMO-3 running NEMO detector is robust NEMO can measure each component of its background External 208Tl: external (e-,g) channel External neutrons and g: crossing e- above 4 MeV Internal 208Tl impurities: internal (e-,Ng) channel, A<100 mBq/kg Internal 214Bi impurities and Radon: (e-,delayed a) channel from Bi-Po process Radon was the dominant background supressed by radon-free air surrounding the detector Very low levels of background have be achieved with ~ 10 kg of isotopes Expected sensitivity after 5 years of data (with FWHM ~ 15% @ 1 MeV) with 7 kg of 100Mo: T1/2(bb0n) > 4 .1024 y  <mn> < 0.2 – 0.35 eV (90% C.L.) with 1 kg of 82Se: T1/2(bb0n) > 8 .1023 y  <mn> < 0.65 – 1.8 eV (90% C.L.)

Can we increase the mass of isotope Question : Can we increase the mass of isotope with such a detector ?

SuperNEMO: a futur detector with ~100 kg of 82Se Zero background experiment with a direct signature of the two emitted e-  To reach a sensitivity ~ 50 meV bb(0n) ? Klapdor et al. Phys. Lett. B 586(2004), 198-212 Test Klapdor’s claim T 1/2 (0n) = (0.69 - 4.18) 1025 y (90% C.L.) 0.1 eV < mn < 0.9 eV NEMO-3 Access to inverted hierarchical mass spectrum SuperNEMO

2b2n bkg with 100 kg of 82Se  2b2n bkg with 7 kg of 100Mo T1/2 (2b2n) = 7.1018 years for 100Mo = 1020 years for 82Se 2b2n bkg with 100 kg of 82Se  2b2n bkg with 7 kg of 100Mo > e A M . t Nexcluded ln2 . N (years) M: Mass of isotope bb (g) e: Detection efficiency With e ~ 0.2 (as NEMO-3) M = 100 kg of 82Se « Zero Background »  Energy resolution FWHM < 8% @ 1 MeV 5 years of data: T1/2 (0n) > 2.1026 y  mn < 40 – 100 meV 10 years of data: T1/2 (0n) > 4.1026 y  mn < 30 – 70 meV

Example of a module of SuperNEMO: « extrapolation of NEMO-2-3 » Module 4 x 4 x 1 m3 Source 3 x 3 m2 ~ 5 kg of 82Se 1000 scintillator blocs (20 x 20 x 10) cm + PMTs 8’’ 4 m 1 m 4 m 3 m 3 m 4 m

etc… Example of a SuperNEMO = 20 modules with water shield ~ 9 m large, ~ 12 m high to remove a module… ~ 70 m long !… ~ 1.5 m ~ 5 m etc… Water shield Coil for Magnetic field

Program R&D during 2 years Calorimeter FWHM = 7 % scintillator + PMT Collaboration France (CENBG), Dubna, Kharkov, UCL and Photonis Light collection to decrease number of PMT separate e- calorimeter (thin scintillator) and g tagging (larger scinttilator) Source R&D purification 82Se in INEEL (USA) 208Tl ~5mBq/kg and 214Bi 20 mBq/kg (factor 10 / NEMO3) Production of 2 kg of 82Se with ILIAS (Russia) Active sources 20 mm (LAL, Russia, INEEL) e- e- Tracking Full plasma propagation with Geiger cells of 4 m long (LAL) reduce Diameter /or mass of wires a/e- tagging beetween active sources e- e- Simulations (IRES, LPC Caen) Geometry Shielding … Active source Proposal for R&D and first module in preparation with british collaborators

CONCLUSIONS Almost 2 years of NEMO-3 running have demonstrated that NEMO detector is robust Detector can measure each component of background origines of background are understood very low backgrounds have been achieved (as the proposal) Possible to extrapolate such a detector to a SuperNEMO detector with ~100 kg of 82Se to reach ~ 50 meV Pragmatic experimental approche Proposal for 2 years of R&D and construction of a 1st module is under preparation