1. MOON for next-generation neutrino-less double beta decay experiment ; present status and perspective Outline of the MOON detector Background rejection & Expected sensitivity R&D Summary T. Shima Research Center for Nuclear Physics, Osaka University for the MOON collaboration TAUP2007, Sendai, September 11-15, 2007

2. MOON collaboration H. Ejiri* (CTU-Praha, RCNP/Osaka and NIRS) T. Itahashi, K. Matsuoka, M. Nomachi, S. Umehara (Phys./OULNS, Osaka Univ.) T. Shima (RCNP, Osaka Univ.) K. Fushimi, K. Yasuda, Y. Kameda (GAS, Univ. of Tokushima) R. Hazama (Hiroshima Univ.) H. Nakamura (NIRS) S. Yoshida (Tohoku Univ.) T. Kii (IAE, Kyoto Univ.) P.J. Doe, R.G.H. Robertson*, D.E. Vilches, J.F. Wilkerson, D.I. Will (CENPA, Univ. Washington) S.R. Elliott, V. Gehman (LANL) J. Engel (Phys. Astronomy, Univ. North Carolina) M. Finger, M. Finger, K. Kuroda, M. Slunecka, V. Vrba (Phys. Charles Univ. and CTU-Praha) M. Greenfield (ICU, Tokyo) A. Para (FNAL) A. Sissakian, V. Kekelidze, V. Voronon, G. Shirkov, A. Titov (JINR) V. Vatulin, P. Kavitov (VNIIEF) * Contact persons.

3. Goal of next-generation DBD experiments QD: 100~200 meV NEMO3 CUORITINO IH: 50~25 meV Next-generation: Super-NEMO, MOON NH: 4~2 meV Future experiment KKDC 440meV  13 2 Thermal Leptogenesis scenario favors 1meV < m < 0.1eV Astronomical observations (PLANCK, Ly-a, weak lensing etc.) will provide constraints of 25~65meV on m.

4. 0  nuclear matrix element IsotopeQ  [MeV]G 0 [10 -14 yr - 1 ] M 0 G 0 ·|M 0 | 2 76Ge2.0390.442.80-4.333.45-8.25 82Se2.9921.892.53-3.9812-30 96Zr3.3513.951.49-3.558.8-49.8 100Mo3.0343.170.77-4.671.9-69 116Cd2.8043.241.09-3.753.85-45.6 128Te0.8760.122.17-4.580.57-2.52 130Te2.5292.861.80-3.599.3-36.9 136Xe2.4673.030.66-4.641.3-65 150Nd3.36813.43.33-4.51149-273

5. MOON Mo/Majorana Observatory Of Neutrino 1 unit = 42 modules = 20kg  source 10~30mm 15mm 20~40mg/cm 2

6. Detectors Plastic scintillators (2m×1m×15mm/layer) :  -ray energy & time,  -ray veto FWHM  E/(E 1 +E 2 ) = 7%@3MeV → 5% Wire chambers (2m×1m×10~30mm/layer) : gas mixture; Ar+CO 2 particle ID;  /  correction for position dependent response of PLs delayed anti-coincidence with ,  position separation of 5mm×5mm (wire-spacing + charge-division or anode×cathode) Active shieldings : thick PL or NaI

7. Features Compact and modular structure scalable from sub-tons to multi-tons easy to shield against external & internal BG’s large acceptance Multi-layers of source foils, scintillators and wire chambers capability to measure different  nuclei sensitivity to  energy- and angular- correlations good selectivity of  and BG with information of E, t, position

8. Real-time detection of low-energy solar Real-time detection of low-energy solar pp 7 Be pep 8B8B

9. Backgrounds RI impurities with large Q  : 214 Bi, 208 Tl (n,n’  ), (n,  ) by  -induced neutrons 2  :  2 /  0 > ~1/10 5

10. 208 Tl (Q  =4.999MeV) :  -  -  in source foil    anti-coincidence by  1 coincidence with MWPCs on both sides of source --- to be rejected with

11. Response for 1.8MeV  +583keV  +2614keV  Gate condition Counts in 2.9-3.2 MeV [ /ton/yr] E 1 +E 2 > 0keV5280 E 1, E 2 > 500keV2640 Veto by other PL9 MWPCs on both sides coincidence 0.32 Track consistency0.28 20mBq/ton 208 Tl in 100 Mo ~0.3 events for 1 ton·yr measurement

12. Neutron-induced  -rays Main components of MOON detector; 12 C, 1 H, 100 Mo, etc. Quantity [mole/unit]  (inelastic) (average) [b]  (capture) (thermal) [b] 12 C1.1×10 5 0.40.0034 1H1H2.2×10 5 00.332 100 Mo2000.90.2 82 Se2440.80.799 150 Nd1331.2515.9 1 H(n,  ) 2 H ; Q=2.225MeV << Q  of 100 Mo, 82 Se, 150 Nd…

13. Production rates of neutron-induced  ReactionR  [unit -1 s -1 ] 12 C inelastic (4.44MeV)2.1×10 -6 100 Mo inelastic3.3×10 -8 12 C thermal capture1.9×10 -8 100 Mo thermal capture5.5×10 -9 Total2.2×10 -6  n (E n < 20MeV) ~10 -8 n/cm 2 /MeV/s at 2000m w.e. (Gaitskell 2001)

14. Response for 5MeV  0  window ~0.2 events for 1 ton·yr measurement at 2000m w.e.

15. Estimated background rates ; summary Background sourceRate [/ton/yr] 208 Tl  -  -  in source <~0.6 214 Bi  -  in source ~0.1 214 Bi  (1 - → 0 + ) <0.01 Two external 2614keV  s acc. coin. ( for 0.1Bq/kg 232 Th) ~0.03 Neutron-induced  0.2~1 100 Mo 2  (FWHM=5%) 4.1 Total~6

16. Sensitivity for ; 100 Mo 0 

17. Sensitivity vs. Energy resolution MOON-1 MOON-1 (correct for position)

18. MOON-1 6-layers of PL 53×53×1cm 3, Mo-Foil 142g @20mg/cm 2 ×2 H. Ejiri, Czeck. J. Physics, 56 (2006) No 5, 459. H. Nakamura, et al., nucl-ex/0609008  E/E(FWHM) = 7% at 3MeV → 5% with correction for position dependence PLsMo foilsPMTs

19. R&D; prototype NaI(Tl) scintillator provided by Horiba, Ltd. 150mm×150mm×10mm slab, three PMTs on each side better energy resolution for  and BG  s sensitivity for  to excited states

20. Summary MOON is one of the feasible solutions for next-generation 0  experiment, because of its high efficiency, good resolutions (E, x, t), compactness, scalarbility, etc. - Road map - PhaseN  [t] ×T [y]T 1/2 10 26 [y] [meV] 82 Se 100 Mo I0.03 × 40.9113105122107 II0.12 × 43.566597666 III0.48 × 410.140344941 FWHM= 5% or 4% @3MeV Cf. Next-generation 76 Ge experiments ; 1ton×4yr ⇒ ~40meV

21. 214 Bi (Q  =3.27MeV) : single  energy losses in both PLs > 500keV  -ray track positions in MWPCs (5mm×5mm) --- rejected with

22. Response for 214 Bi single  Gate condition Counts in 0  window [ /ton/yr] E 1 +E 2 > 0keV713 E 1, E 2 > 500keV0.91 Veto by other PL0.83 MWPC coin.0.002 Track consistency0.002 20mBq/ton 214 Bi in 100 Mo ~0.002 events for 1 ton·yr measurement

23. 214 Bi (Q  =3.27MeV) :  -  anti-coincidence by Compton-scattered  coincidence with MWPCs on both sides of source --- rejected with

24. Response for 214 Bi  -  Gate condition Counts in 0  window [ /ton/yr] E 1 +E 2 > 0keV44 E 1, E 2 > 500keV23 Veto by other PL9 MWPCs on both sides coincidence 0.09 Track consistency0.09 20mBq/ton 214 Bi in 100 Mo ~0.1 events for 1 ton·yr measurement

25.  -induced neutrons Energy spectrum:  n (E n < 20MeV) ~10 -8 n/cm 2 /MeV/s

26. 12 C+n cross sections

27. Inelastic   n [n/s]  n,n ’ > [b] N [atoms/b]R  [s -1 ] 12 C 2.8 × 10 -6 (4.4~20MeV) 0.41.86 2.1 × 10 -6 100 Mo 3.6 × 10 -6 (<20MeV) 0.90.01 3.3 × 10 -8 ( for one unit (42 modules, 20kg 100 Mo) )

28. Capture  ( i = 12 C, 100 Mo, or 1 H ) Assuming all neutrons are thermalized and captured inside the detector…. 37473000 [b·mole/unit]40

29. Accidental Coincidence of external 2614keV  -rays Response for 2614keV single  -ray (0.1Bq/kg 232 Th in PMTs) Gate conditionSuppression Total1 E>500keV0.47 Veto with other PLs0.035 MWPC coin.6.3e-4 Single track5.3e-4

30. Coincidence rate Number of PMT (/unit)4300 Mass of PMT (kg/unit)3010 Gamma Rate (/s/unit) ; 100mBq/kg 301 Count Rate (/s/unit) ;  =1.6  120.4 Count Rate (/yr/unit)3.80E+09 Single Track (ratio)0.022 Single Track (/yr/unit)8.31E+07 Coincidence (ratio)0.11 Coincidence Time (sec)1.00E-05 Vertex (ratio)2.54E-06 Coincidence Rate (/yr/unit)6.07E-04 Coincidence Rate (/yr/ton)3.03E-02