Sei Yoshida Research Center for Neutrino Science, Tohoku University

Transcription

1 Sei Yoshida Research Center for Neutrino Science, Tohoku University

2 S.Abe 1, T.Ebihara 1, S.Enomoto 1, K.Furuno 1, Y.Gando 1, H.Ikeda 1, K.Inoue 1, Y.Kibe 1, Y.Kishimoto 1, M.Koga 1, Y.Minekawa 1, T.Mitsui 1, K.Nakajima 1, K-H.Nakajima 1, K.Nakamura 1, M.Nakamura 1, K.Owada 1, I.Shimizu 1, Y.Shimizu 1, J.Shirai 1, F.Suekane 1, A.Suzuki 1,Y.Takemoto 1, K.Tamae 1, A.Terashima 1, H.Watanabe 1, E.Yonezawa 1, S.Yoshida 1, A.Kozlov 2, J.Busenitz 3, T.Classen 3, C.Grant 3, G.Keefer 3, D.Leonard 3, D.MaKee 3, A.Piepke 3, M.P.Decowski 4, J.A.Detwiler 4, S.J.Freedman 4, B.K.Fujikawa 4, F.Gray 4,E.Guardincerri 4, L.Hsu 4, K.Ichimura 4, R.Kadel 4, K.-B.Luk 4, H.Murayama 4, T.O Donnell 4, H.M.Steiner 4, L.A.Winslow 4, D.A.Dwyer 5, C.Jillings 5, C.Mauger 5, R.D.McKeown 5, C.Zhang 5, B.E.Berger 6, C.E.Lane 7, J.Maricic 7, T.Miletic 7, M.Batygov 8, J.G.Learned 8, S.Matsuno 8, S.Pakvasa 8, J.Foster 9, G.A.Horton-Smith 9, A.Tang 9, S.Dazeley 10, K.Downum 11, G.Gratta 11, K.Tolich 11, W.Bugg 12, Y.Efremenko 12, Y.Kamyshkov 12, O.Perevozchikov 12, H.J.Karwowski 13, D.M.Markoff 13, W.Turnow 13,K.M.Heeger 14,F.Piquemal 15, and J.-S.Ricol Research Center of Neutrino Science, Tohoku University 2. IPMU, The University of Tokyo 3. Department of Physics and Astronomy, University of Alabama 4. Physics Department, University of California Birkeley/ Lawrence Berkeley National Laboratory 5. W.K.Kellogg Radiation Laboratory, California Institute of Technology 6. Department of Physics, Colorado State University 7. Physics Department, Drexel University 8. Department of Physics and Astronomy, University of Hawaii at Manoa 9. Department of Physics, Kansas State University 10. Department of Physics and Astronomy, Louisiana State University 11. Physics Department, Stanford University 12. University of Tennessee 13. Triangle Universities of Nuclear Laboratory/Physics Department, Duke University 14. Department of Physics, University of Wisconsin 15. CEN Bordeaux-Gradignan, IN2P3-CNRS and University Bordeaux I August 28-29th,

3 KAMioka Liquid scintillator Anti-Neutrino Detector Inner Detector Liquid Scintillator (1000 tons) Ultra-pure ; U/Th < g/g 1.36 g/l 1 kt Liquid Scintillator PMTs KamLAND Detector Plastic Balloon (13 m diameter) Mineral Oil : Inner buffer ρ LS /ρ MO = PMTs 1325 of 17-inch and 554 of 20-inch Photo-coverage : 34% ~ 500 p.e./mev Outer Detector Water Cherenkov detector ; muon veto PMT 225 of 20-inch August 28-29th,

4 1 km Horizontal access 2700 m.w.e DAQ and Electronics and Calibration system Water purification System Ge Detector Heat exchanger and Pumping station New 2 nd Purification Area Distillation System, Nitrogen Purge, LS Quality Control Systems (area not shown) 1 st Purification Area Liq.-Liq. Extraction and Nitrogen Purge August 28-29th,

5 Measurement of 7 Be solar neutrino flux. Put more stringent limits on CNO cycle contribution to the solar neutrino flux. Reduce 13 C(α,n) 16 O background for reactor and geo-ν measurements, caused by 210 Po α-decay. Anti-neutrino spectrum August 28-29th,

6 Single Energy Spectrum Observed in KamLAND Before Purification Fiducial R < 4 m Main sources of background in the range of 7 Be neutrino 210 Pb( 210 Bi 210 Po ), 40 K by distillation 85 Kr by N 2 purging pep/cno neutrino ; 11 C by tagging neutron August 28-29th,

7 T 1/2 Activities (Before purif.) Purification Goal Required Reduction 210 Pb 22.3 y 40 mbq/m 3 1 µbq/m ~ K 10 9 y g/g g/g U 10 9 y g/g g/g OK 232 Th y g/g g/g OK 85 Kr 11 y 400 mbq/m 3 1 µbq/m ~ Rn 3.8 d < 10 µbq/m August 28-29th,

8 Online purification with the flow rate ~ 1 m 3 /h. Distillation System; 210 Pb, 210 Bi, 210 Po, 40 K N 2 purge system ; 85 Kr, 39 Ar, and 222 Rn pure N 2 gas N 2 Generator August 28-29th,

9 Newly developed/constructed N 2 generator Supply air : Rn less air from outside of mine N 2 supply capacity : 40 Nm 3 /h Purity Ar Emergency 5 Nm 3 /h from Liq. N ~ 0.03ppm (measured) Kr ~10-15 (not measured yet) 222 Rn ~ 5 µbq/m 3 (measured at purif. Area) August 28-29th,

10 August 28-29th,

11 Liquid scintillator(ls) is fed into small buffer tank (2 m 3 ) from KamLAND. Different boiling point August 28-29th,

12 Pseudocumene(PC) is distilled firstly Operating pressure 2 kpa. Boiling point ~ 60 Rest at the bottom of PC tower Dodecane + PPO send to next tower August 28-29th,

13 Dodecane(NP) is distilled secondly. Operating pressure ~2 kpa. Boiling point ~ 100 Rest at the bottom of NP tower Dodecane + PPO(little concentrated) send to PPO concentrator (~140 under 2 kpa), NP is evaporated back to NP tower. August 28-29th,

14 PPO is distilled finally. Operating pressure ~0.3(2 nd Phase) ~ 0.6(1 st Phase) kpa. Boiling point ~ 160 ~ 190 Rest at the bottom of PPO tower Exhaust August 28-29th,

15 LS is mixed (blended) with distilled PC,NP, and PPO. Temperature sensor and Density meter PC and NP mixture is adjusted by pre-small tank. PPO is mixed with PC ~ 10 wt%, then fed into mixture tank. August 28-29th,

16 Purging by pure N 2 gas Operating pressure ~ 40 kpa N 2 flow rate ~ 30 Nm 3 /h Series of Gas Liq. Mixer, and Gas-Liq. Separator August 28-29th,

17 Purpose is to insure high levels of purification and prevent recontaminating after purification procedure 39 Ar and 85 Kr measurement system gives us sensitivity to low concentrations (10 µbq/m 3 ) by using a cold trap and RGA. Assumes secular equilibrium with natural isotopic abundances. 222 Rn measurements. Two devices α counting by electrostatic collection method after trapping Rn ~1 m 3 scintillation detector to measure 214 Bi-Po coincidences (miniland) Sensitivities ~ 10 µbq/m 3 Optical Properties Light Attenuation Length Light Yield Density ; Accuracy ~ 10-5 PPO concentration Gas Chromatography August 28-29th,

18 1 st Purification Phase : May/12/2007 ~ Aug/01/2007 Purified ~ 1500 m 3 from the top Purification was stopped, because mining company was blasting for a new cavity. Problems in 1 st Phase: Mixing was seen in Bi-Po signal. 10 % loss in light yield seen after one volume transfer The activities are still high for 7 Be and pep/cno ν. Worse reduction for 85 Kr considered due to the leak in the chimney. 2nd Purification Phase : Jun/16/2008 to Feb/06/2009 Three full volume transfers were performed. Changed to bottom filling after completing first volume transfer. August 28-29th,

19 Online monitoring 214 Bi-Po ( 222 Rn daughter) Distribution Vertex distribution (0.45 MeV < E < 0.70 MeV) 1 Starting purification 2 Keeping boundary 3 Dropping purified LS along balloon surface 4 Mixing purified LS with old LS 5 Re-making new boundary with lighter LS 6 Stopping 1 st purification phase August 28-29th,

20 Vertex distribution (0.45 MeV < E < 0.70 MeV) August 28-29th,

21 Online purification was accomplished by the 2 nd purification. Offline data analysis is being progressed. BG reduction ; 10-4 ~ 10-5 in the 7 Be-ν range (α,n) background was reduced. negligible background for geo-ν measurement. 8 B solar-ν measurement Threshold energy pushing down to 3 MeV. August 28-29th,

22 New purification system was constructed. Distillation & N 2 purge. Pure N 2 gas generator Online purification was performed. 1 st and 2 nd phase of purification has been accomplished. Offline data analysis is being progressed. Reduced BG ; 10-4 ~ 10-5 in the 7 Be-ν range (α,n) background was reduced. negligible background for geo-ν measurement. 8 B solar-ν measurement Threshold energy pushing down to 3 MeV. Data taking will be continued till ~Feb./2011 Move to the next phase ; 0νββ of 136 Xe August 28-29th,