Double Beta experiment using nuclear emulsions? M. Dracos Double Beta experiment using nuclear emulsions? Marcos Dracos IPHC/IN2P3, Strasbourg M. Dracos, Bologna, 01/09/2008

Double Beta Decay ? L=2 T 1/2 ~ 1019-1020 years ! M. Dracos Double Beta Decay double beta without neutrino L=2 allowed double beta T 1/2 ~ 1019-1020 years ! Observed for: Mo100, Ge76, Se82, Cd116, Te130, Zr96, Ca48, Nd150 ? T1/2= F(Qbb,Z) |M|2 <mn>2 -1 Phase space factor Nuclear matrix element Effective mass: <mn>= m1|Ue1|2 + m2|Ue2|2.eia1 + m3|Ue3|2.eia2 |Uei|: mixing matrix elements, a1 and a2: Majorana phases 5 M. Dracos, Bologna, 01/09/2008

Neutrino mass hierarchy M. Dracos Neutrino mass hierarchy m2 m12 m22 m32 Degenerate m1≈m2≈m3» |mi-mj| Normal hierarchy m3>>> m2~m1 Inverted hierarchy m2~m1>>m3 ? Degenerate Goal of next generation experiments: ~10 meV Inverted hierarchy Lower bounds! Normal hierarchy | mee| in eV M. Dracos, Bologna, 01/09/2008 Lightest neutrino (m1) in eV

Present detection techniques or under investigation M. Dracos Present detection techniques or under investigation Calorimeter Semi-conductors Source = detector Calorimeter (Loaded) Scintillator Source = detector Tracko-calo Source  detector Xe TPC Source = detector b b b b b b b b e, DE e, M e,M isotope choice good energy resolution better background rejection CANDLES NEMO3 CUORE CaF2(Pure) EXO M. Dracos, Bologna, 01/09/2008

Isotopes isotopes used by NEMO3 experiment at Fréjus Isotope Q(keV) M. Dracos Isotopes Isotope Q(keV) 116Cd116Sn 2804.74.2 82Se82Kr 2995.23.3 100Mo100Ru 3034.86.3 96Zr96Mo 3350.03.5 150Nd150Sm 3367.14.9 48Ca48Ti 4272.04.1 Bckg sourcesthicknessmg/cm2) 82Se (0,93 kg) isotopes used by NEMO3 experiment at Fréjus M. Dracos, Bologna, 01/09/2008

plastic scintillator blocks M. Dracos The NEMO3 detector expected sensitivity up to mn~0.3 eV plastic scintillator blocks 3m + photomultipliers (Hamamatsu 3", 5") wire chamber (Geiger) energy and time of flight measurements Sources : 10 kg, 20 m2 2 electron tracks M. Dracos, Bologna, 01/09/2008

M. Dracos Event Examples M. Dracos, Bologna, 01/09/2008

Results T1/2(bb0n) > 5.8 1023 (90 % C.L.) M. Dracos Results 932 g 389 days 2750 even. S/B = 4 Phase I + II 693 days T1/2(bb0n) > 5.8 1023 (90 % C.L.)  <mn> <0.6-2.5 eV 100Mo ( 7 kg ) 82Se Expected in 2009 T1/2(bb0n) > 2 1024 (90 % C.L.)  <mn> <0.3-1.3 eV 82Se T1/2 = 9.6 ± 0.3 (stat) ± 1.0 (syst)  1019 y 116Cd T1/2 = 2.8 ± 0.1 (stat) ± 0.3 (syst)  1019 y 150Nd T1/2 = 9.7 ± 0.7 (stat) ± 1.0 (syst)  1018 y 96Zr T1/2 = 2.0 ± 0.3 (stat) ± 0.2 (syst)  1019 y 48Ca T1/2 = 3.9 ± 0.7 (stat) ± 0.6 (syst)  1019 y 48Ca background subtracted M. Dracos, Bologna, 01/09/2008

Super NEMO R&D up to 2009, construction M. Dracos Super NEMO Improvements: Energy resolution 15%  DE/E = 4% @ 3 MeV Efficiency 15%  20 - 40% @ 3 MeV Source x10 larger 7kg  100 - 200 kg Most promising isotopes 82Se (baseline) or perhaps 150Nd Aim: T1/2 > 2 x 1026 y   Mbb  < 40 - 90 meV R&D up to 2009, construction between 2010 and 2013 (if approved) source sheet M. Dracos, Bologna, 01/09/2008

2 with emulsions e e "veto" emulsion, if needed M. Dracos 2 with emulsions "veto" emulsion, if needed (~50 m like in OPERA?) e e beta source (~50 m in NEMO3 could be less for emulsions) plastic base "2" emulsion thick enough to detect up to 4 MeV electrons (density?) M. Dracos, Bologna, 01/09/2008

Tests in Nagoya using OPERA emulsions M. Dracos A. Ariga, diploma thesis electron spectrometer 50 m M. Dracos, Bologna, 01/09/2008

Electron tracks in emulsions M. Dracos Electron tracks in emulsions 1 MeV e- simulation 100 m simulation 2 MeV e- (A. Ariga and NIM A 575 (2007) 466) M. Dracos, Bologna, 01/09/2008

2 with emulsions NEMO3 surface: 20 m2 Super-NEMO surface: 10x20 m2 M. Dracos 2 with emulsions NEMO3 surface: 20 m2 Super-NEMO surface: 10x20 m2 To cover the same isotope source surface with emulsions (both sides to detect the 2 electrons) we need an emulsion surface: 2x200=400 m2. Just for comparison, one OPERA emulsion has a surface of about 0.012 m2 and one brick 0.680 m2. So 400 m2 is about the equivalent of 600 OPERA bricks over 150000 (but not with the same thickness of course, taking into account the thickness this could be the equivalent in emulsion volume of about 25000 OPERA bricks). Use the same envelops like the OPERA changeable sheets by introducing at the middle of the two emulsions (or stack of emulsion sheets) a double beta source sheet. Keep all these envelops for some time (e.g. 6-12 months) in the experiment and after this period start scanning them one after the other. They could be replaced by new envelops during 5 years in order to accumulate something equivalent to what Super-NEMO could do: 5*400 year*m2 Experiment volume: <5 m3  very compact experiment! M. Dracos, Bologna, 01/09/2008

Previous tentative Conclusion: 1.28 g 96Zr (powder) M. Dracos Previous tentative 1.28 g 96Zr (powder) source thickness: 180 m total exposure time: 3717 hours scanned surface for electron pairs: 10 mm2 estimated total efficiency: 18% Conclusion: T1/2(96Zr)>1017 years, decrease the thickness of the isotope layer, use low radioactivity emulsions, scanning speed has to considerably be increased (automatic scanning needed). M. Dracos, Bologna, 01/09/2008

M. Dracos Emulsion scanning How much time is needed to make a full scan of 2000 m2 (full scan in all volume not needed, just follow tracks present in the emulsion layer near the isotope foil)? If the Japanese S-UTS scanning system is used with a speed of 50 cm2/hour, for one scanning table: 25 m2/year (200 working days/year). By using 16 tables and extracting 100 m2/3 months (1 year exposure at the beginning and putting back new emulsions with the same isotopes), this finally will take less than 5 years (as Super-NEMO). Probably the emulsion thickness needed to detect these electrons will need more scanning time and the speed would be significantly less than 50 cm2/h. On the other hand, scanning speed increases with time… 0.003 0.1 1.2 7.0 40 60 140 700 0.001 0.01 1 10 100 1000 cm 2 / h TS(1994) NTS(1996) UTS(1998) SUTS(2006) SUTS(2007-) Scanning Power Roadmap 1stage facility CHORUS DONUT OPERA Nakamura san Nufact07 M. Dracos, Bologna, 01/09/2008

Pending questions Energy resolution for NEMO: 15% for 1 MeV electrons M. Dracos Pending questions Energy resolution for NEMO: 15% for 1 MeV electrons Required for Super-NEMO: lower than 8% Emulsion experiment energy resolution: ??? Overall reconstruction efficiency for NEMO: 15-18% Required for Super-NEMO: >30% Emulsion experiment reconstruction efficiency: ?? Minimum electron energy (~0.5 MeV?, 0.200 MeV for NEMO3), will greatly influence the total efficiency. Afforded background? Possibility to take thinner isotope sheets (60 m for NEMO3) and have better energy resolution (but also more scanning for the same isotope mass, find good compromise). M. Dracos, Bologna, 01/09/2008

Possible isotopes to be used M. Dracos Possible isotopes to be used For emulsions the electron detection threshold cannot be so low than NEMO3 (200 keV, low density material gas+plastic scintillator)  utilisation of high Q-value isotopes>3 MeV advantage: low background, high efficiency problem: low abundance M. Dracos, Bologna, 01/09/2008

Feasibility studies 207Bi source with well known activity M. Dracos Feasibility studies 207Bi source with well known activity (EICe-=976, 482 keV) emulsion sheets 0.6 mm thick (3-4 layers) Reconstruction efficiency: by counting the number of reconstructed electrons from both energy lines after scanning (this would help to tune the algorithms). Electron threshold: the reconstruction efficiency for both electrons (mainly those at 482 keV) would give a good idea about the threshold. Energy resolution: by counting the associated grains to the track, by measuring the track range. Afforded background: perform the above tests with different backgrounds. Needed scanning tables, low radioactivity lab (Gran Sasso, Baksan, Fréjus…), thick emulsions (refreshed in low radioactivity lab). M. Dracos, Bologna, 01/09/2008

Limitations high multiple scattering for low energy electrons M. Dracos Limitations high multiple scattering for low energy electrons de/dx fluctuations bremsstrahlung gammas (energy lost) lost -electrons electron backscattering 0.7 MeV e- (10 tracks) d=2.7 g/cm3 (Geant 3.2) better to use low density emulsions? M. Dracos, Bologna, 01/09/2008

Extra Ideas e e e e emitter in powder (diluted in an emulsion layer) M. Dracos Extra Ideas e e e e emitter in powder (diluted in an emulsion layer) decreasing density (25 m layers) better vertex and energy reconstruction? (few isotopes are anyway in powder form) to minimize the emulsion thickness and better energy resolution at the end of the track M. Dracos, Bologna, 01/09/2008

BACKGROUND EVENTS OBSERVED BY NEMO-3 and rejection in emulsions M. Dracos BACKGROUND EVENTS OBSERVED BY NEMO-3 and rejection in emulsions end of tracks easily recognised in emulsions  rejection alpha tracks easily recognised in emulsions  rejection Electron crossing > 4 MeV Neutron capture Electron + a delay track (164 ms) 214Bi  214Po  210Pb cannot be rejected in absence of magnetic field  good emulsion shielding no vertex or very good vertex resolution in emulsions  rejection  Electron + N g’s 208Tl (Eg = 2.6 MeV) Electron – positron pair B rejection M. Dracos, Bologna, 01/09/2008

bb0n-like event due to Radon from the gas (NEMO3) M. Dracos bb0n-like event due to Radon from the gas (NEMO3) E1+E2= 2880 keV a track (delay = 70 ms) 214Po  210Pb 214Bi  214Po decay IN THE GAS Run 2220, event 136.604, May 11th 2003 M. Dracos, Bologna, 01/09/2008

NEMO3 main background configurations M. Dracos NEMO3 main background configurations Proportion of types of events in raw data: Type of event Rate (mHz) 1 e-, 0g 600 1 e-, Ng (N1) 150 e+e- pairs 110 Crossing e- 80 bb event 5.4 mHz M. Dracos, Bologna, 01/09/2008

M. Dracos Conclusion Technology allows now the investigation about observation of double beta decays using nuclear emulsions To prove the experiment feasibility few questions have to be answered: what is the energy resolution? what is the afforded background? what is the overall efficiency? The above questions could be answered with relatively low investment. M. Dracos, Bologna, 01/09/2008

M. Dracos END M. Dracos, Bologna, 01/09/2008