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First results from NEMO 3 Experiment

This article discusses the NEMO3 experiment and its goal of searching for neutrinoless double beta decays. It covers the detector's performances, background results, data analysis, and preliminary findings.

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First results from NEMO 3 Experiment

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  1. First results from NEMO 3Experiment V. Vasiliev (ITEP), H. Ohsumi (Saga) and Ch. Marquet (CENBG) @NDM03, Nara, Japan, June 2003 NEMO collaboration

  2. NEMO 3 collaboration CENBG, IN2P3-CNRS andUniversityof Bordeaux, France CFR, CNRS Gif sur Yvette, France Czech Technical University, Prague, Czech Republic INEEL, Idaho Falls, USA IReS, IN2P3-CNRS and Universityof Strasbourg, France ITEP, Moscow, Russia JINR, Dubna, Russia Jyvaskyla University, Finland LAL, IN2P3-CNRS and University of Paris-Sud, France LPC, IN2P3-CNRS and Universityof Caen, France Mount Holyoke College, USA Saga University, Japan University College London, UK

  3. (I) H. Ohsumi (and Ch. Marquet) 1. Introduction (about our final goal) 2. Detector Performances, Present status, Backgrounds 3. An example of background results (Cu foils) (II) V. Vassiliev 4. Present status of the data analysis 5. Preliminary results of the first stage 6. Conclusions

  4. Just to remind you the original idea of NEMO Neutrinoless Double Beta Decays (0nbb) Majorana n ? <mν> ? or new physics ? Measureseveral isotopes (0nbb, 2nbb) 100Mo, 82Se, 130Te, 116Cd, 96Zr, 48Ca, 150Nd Tag and measure all the BG events e-, e+, g, a, neutron Tracking chamber+Calorimeter+B-field+Shields → “zero background” experiment 2nbb 0nbb E(b1+b2) Qbb

  5. (25 G) B 3 m 4 m The NEMO3 detector Fréjus Undergroud Laboratory : 4800 m.w.e. 20 sectors Source :  isotopes (7kg 100Mo, 1kg 82Se…..) cylindrical, S = 20 m2, e = 60 m Tracking detector :He+ alcohol(5%) +Ar(1%) drift wire chamber operating in Geiger mode (6180 cells) Calorimeter: 1940 plastic scintillators coupled to low radioactivity PMs (E)/E at 3 MeV ~ 3.5% Magnetic field:25 Gauss Iron shielding: e = 20cm Neutron shielding: water +wood+parafin Identification : e-, e+, , n and delayed-   events detection  Measurement of source radiopurity  Background measurement and rejection

  6. 1 sectorof NEMO3 NEMO3 : Neutrino Ettore Majorana Observatory Tracking detector (6180 Geiger cells in He+alcohol(5%)+Ar(1%)): Vertex st=4 mm, sz = 0.8cm Calorimeter (1940 plastic scintillators– PMTs low radioactivity)FWHM~14% (e-@1 MeV) Iron shield (20cm) + water shield + wood shield + parafin magnetic field B=25 G materials low radioactivity Frejus Underground Laboratory (LSM) 4800m.w.e.

  7. October 2001

  8. July 2002

  9. Sources preparation

  10. Sources bb (thickness ~ 60 mg/cm2) bb(2n) Bkg 100Mo (6.9 kg) 82Se (0.93 kg) NBkg=0,02 evts y-1 kg-1 NBkg=0,2 evts y-1 kg-1 Qbb = 3034 keV Qbb = 2995 keV > 8. 1024y > 1,5 1024y <mn> < 0,1 – 0,3 eV <mn> < 0,45 – 1,2 eV (90% C.L.) (90% C.L.) Sources in NEMO-3 detector Requirements: <0.02mBq/kg(208Tl) <0.3mBq/kg(214Bi) Expected Sensitivity after 5 years : ~0,11(bb2n) <0,04(214Bi) <0,04(208Tl) ~0,01(bb2n),....

  11. Component Weight (kg) 40K 214Bi 208Tl 60Co Total Activities NEMO 3 Not measured 600 830 300 18 Copper <125 < 25 < 10 < 6 By ultra low level g-ray spectroscopy with Ge Petals Iron 5000 <100 <0.7 <0.3 1.8.4 <17 < 2 2.0.7 4.3.7 • NEMO (200tons) • ~300Bq (214Bi) • Human body (60kg) ~5000Bq (40K) Wires <8 10-3 < 10-3 <6 10-4 10-2 ~300 ~20 Shielding Iron 300  100 180000 <3000 <300 <300

  12. Brief summary of NEMO Performances Identification of e, g, a B=25G • Tracking (Identification e/others) Delayed (<700ms) a track • Calorimeter e(g)~50% (@0.5MeV) Possible for tagging eg, egg, eggg, … • Time of flightst~300ps(@1MeV) External Background rejection • Magnetic Field (Identification e-/e+) 3~5% e-/e+ confusion @ 1~7MeV source foil Signal Dt ~0 ns b- b- bb(0n) decay Internal background g Source contaminations Dt ~0 ns e- b- a Dt ~0 ns b- b- bb(2n) decay External background Dt  3 ns e- Study of Background Process « Crossing e- » g • 214Bi Tagged by e(g)a (~164ms) ( 214Bi->214Po->210Pb) • 208Tl eg, egg, eggg, with g(2.6MeV) or Taggd by e(g) a (~300ns) ( 212Bi->212Po->208Pb) • Neutron Crossing e (4~8MeV) g e- n Dt ~0 ns e+ or e- e+e pairs- Double Compton Compton + Möller How detect signals and tag the background ?

  13. NEMO-3 STATUS • Jan. 2001: first events with 3 first sectors mounted • with no magnetic field and no shield • Sep. 2001: full detector mounted and assembled • Dec. 2001: first events with the full detector • with no magnetic field and no shield • Feb. 2002: Coil (magnetic field) mounted • Mar. 2002: first events with the full detector • with magnetic field (no shield) • Apr. 2002: Iron shield mounted • Jun. 2002  Dec. 2002: Test runs with iron shield + magnetic field • ~1500h (1200h) (Period I) • Dec. 2002  Feb. 2003: Shutdown for the last tuning (to improve reliability) • 14 February 2003 : START TAKING DATA ~2000h (650h) (Period II) • (We will mainly report the data of this period) • And also: • Runs with calibration sources (Sr90, Bi207, Co60) • for energy and time calibration • Runs with neutron source • for tracking vertex resolution: • for testing neutron shielding (water + wood) • Runs for testing iron shield • run with and without iron shield • Radon studies

  14. 1 sectorof NEMO3 Run with calibration sources ( 207Bi example) Distribution of reconstructed vertices Z vertex (cm) Rf vertex (cm) A vertical flat calibration tube Z 207Bi (~220Bq) x 3 x 20 482keV, 976keV (ICE)

  15. Resolution on the 2e- channel s (D Rf) = 0.6 cm s (D z) = 1.8 cm Geometry of the tracking detector s⊥= 0.4 cm s// = 0.8 cm 3 rows Determination of the impact on the scintillator 2 rows Tracking curvature 4 rows Determination of the vertex using 2 conversion electronsof 207Bi vertical drift cells operating on Geiger mode 1 anodic wire (HT  1900 V) 8 cathodic wires (0 V)

  16. 207Bi 976 keV 482 keV 90Sr End point 2,28 MeV Energy Calibration Tube in each sector where calibration sources are introduced (3 positions) 3 electron energies : 486 keV and 976 keV with207Bi, and 2.28 MeV with90Sr 207Bi+90Sr E(keV)=A*ch+B A=3.350±0.034keV/ch B=23.5±9.17 keV

  17. e- 207Bi laser Daily survey with a LASER • Daily check of E (Gain) and t • PMT E linearity (0 ~ 12MeV) • Determination of t-E relation Optical Filters (known transmissions) 900 PM 5” 1040 PM 3” Photodiode (Intensity Monitor) 7 references : 6 PMs coupledto a207Bi source + average on all theNEMO3 PMs

  18. PM : 2.1.1.4 PM : 18.1.1.0 PM : 19.3.1.0 Gain survey for 3 PMs during 2 months(obtained with the laser system) Typical PM Variation then stabilisation few PMs with pathological behaviour

  19. Time Of Flight Rejection An example of 2 track events on 100Mo Foils bb events from the foil External Background (Crossing electron) (Dtmes – Dtcalc) internal hypo. (ns) (Dtmes – Dtcalc) external hypo. (ns) Time Alignment (Studied by 60Co Source) st ~ 300ps @1MeV

  20. 1256 keV 832 keV bb EVENT OBSERVED BY NEMO-3… E1+E2= 2088 keV (Dt)mes –(Dt)theo = 0.22 ns (Dvertex) = 2.1 mm (Dvertex)// = 5.7 mm bb2n event

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

  22. 208Tl Radioimpurity of the 100Mo(7kg) sources Most « dangerous » background for bb0n study Study of the e- g e- 2g e- 3g channels of 208Tl decay (890 hours of data) channel eg egg eggg 100Mo(data) 1 4 0 100Mo(MC) 1.5 1.7 0.3 (MC calculation for 20mBq/kg of 208Tl) Conservative value (90%CL) A(208Tl) < 50 mBq/kg 208Tl Se(ng) = 5 event Preliminary, to be improved with more data (NEMO requirement: 20 mBq/kg)

  23. 214Bi study by NEMO itself 214Bi effect from Radon Electron + a delay track (164 ms) 214Bi 214Po 210Pb 1. Rn level Air in room ~10Bq/m3 (Normal) Inside of NEMO ~30mBq/m3 (Very Low) 2. Process (in He+Alcohol gas) where is 214Bi ? wire ? gas? or foils ? 3. Contributions 2nbb not dangerous 0nbb  less than 2 events/year ( We are in the border line of our requirement) 4. Radon free air facility This fall  reduce factor 2 Next year  reduce ~50 Radon monitor for chamber out gas 70 litter -1500V 214Bi+ 218Po+(?) NEMO requirement : to the source 0.3mBq/kg Sensitivity ~1 mBq/m3 222Rn

  24. DATA Monte Carlo neutrons H Fe+Cu Fe Neutron Background Comparison neutron simulation with Data from a AmBe source (neutrons: <En> 5MeV + : E=4,43 MeV)  • 4,43 MeV stopped by iron shield With Iron shield + B=25 G : Without n shield AmBe source (out of shield) (e- crossing + n) plastic scintillator n fast n thermalized g e- Copper frame Fast neutrons simulation with 20 cm of iron shield  Expected number of events above 2,75 MeV after 5 years With neutron shield 0 eventabove 2.75 MeV (After 5 years): with a rejection factor of ~ 70 -0,8

  25. Sensitivity of NEMO3 to measure sources of background Design NEMO3 for 10 kg: 208 Tl in source foils < 0.02 mBq/kg 214 Bi in source foils < 0.3 mBq/kg neutron flux < 10-8n cm-2 s-1 Sensitivity NEMO3after 1 year of data: 208 Tl in source foils< 2 mBq/kg channel eg ’s (Eg = 2.6 MeV) 212 Bi  212 Po e(g)a (300 ns) 214 Bi in source foils< 2 mBq/kg measured by channel e (g) +a ( 214 Bi  214 Po  210 Pb; T1/2 = 164 ms ) neutrons< 10-9 n cm-2 s-1 measured by e- crossing > 4 MeV a factor 10 better! a factor 100 better! a factor 10 better! Sensitivity to 100 kg of isotopes See A. Barabash talk: NEMO extrapolation

  26. An Example of Background Results (Just for an introduction to the next analysis part) • Cu Foils (0.62kg) （(I)1200h+(II)650h=1850h  78 days) • Using the same analysis of bb decay 0.7 event/day 53 events (78days) No event above 2.6MeV 3MeV Cu E1+E2

  27. Data analisys in NEMO.  22 decay analysis. • Estimation of background. • External  rays. • Rn in the tracking chamber • Radioactive impurities in source foils • Selection of electron-electron (2e) events. • Efficiency estimation. Half-life value. • Consistence of experimental energy and angular • distributions with MC.  20 decay analysis. • Search for candidate 20 events. • Estimate efficiency. • Estimate background. • Conclusion about half-life and neutrino mass.

  28. Background, external .  electron+ events Time of flight  incoming  Good agreement

  29. Background, Rn in the gas.  electron+ events  electron+ delayed  TOF  decay near the source

  30. Background, pollution in source.  single electron events Single electron energy  Ge detector keV Good agreement

  31. Selection of electron-electron events. • 2 tracks reconstructed + 2 associated PMTs • each particle has negative charge • electron energy > 200 keV • Time of Flight  decay inside the source • common vertex • vertex in source material • nearest to the source geiger layer is hit • no delayed geiger hits near the vertex

  32. Mo 22 preliminary results. NEMO 3 Background substracted 22 Monte Carlo 650 hours 13750 events S/B = 40

  33. Mo 22, angular distribution. Background substracted NEMO 3 22 Monte Carlo

  34. Mo 22, HSD and SSD mechanism. HSD, higher levels contribute to the decay SSD, 1+ level dominates in the decay Abad et al., 1984, Ann. Fis. A 80, 9 Calculations for Mo: F. Simkovic et al., J. Phys. G, 27 (2001) 2233-2240 Effect in one electron spectrum • NEMO • High 22 statistics • Measures each electron • could see it!

  35. Mo 22 electrons energy. Background substracted NEMO 3 NEMO 3 Different predictions for T1/2:

  36. Mo 20 preliminary result.  20 decay • 20 energy region [2.75,3.2] MeV • 1 event 20 candidate, 650 h. of • data analysed, no laser corrections. •  = 10 % • Conservative limit  20 decay • energy region [2.6,3.2] MeV • 9 candidate event (650 h.), 5 expected. •  = 0.7 % • Conservative limit

  37. Se 22 preliminary result. NEMO 3 Background substracted 22 Monte Carlo 1850 hours 400 events S/B = 4 Contaminated with -emitters Cuts: E > 300 keV, Cos () < 0.7

  38. Cd 22 preliminary result. Background substracted NEMO 3 22 Monte Carlo 1850 hours 336 events S/B = 3.4

  39. Nd 22 preliminary result. Background substracted NEMO 3 22 Monte Carlo 1850 hours 147 events S/B = 3.1

  40. Conclusion. • NEMO 3 is taking data with stable conditions. • Tracking chamber and calorimeter peｒforme as • expected. • First portion of data analysed and preliminary results for 22 • decay of Mo, Se, Cd and Nd were obtained. • Results for 22 decay of other isotopes (Ca, Zr, Te) are expected • end of the year, and for Mo decay on the excited states will be • available soon. • Search for neutrinoless and majorana 2 decay is in progress.

  41. Summary.

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