a02
play

A02 T. Kishimoto Osaka University CANDLES Collaboration Osaka - PowerPoint PPT Presentation

Aug 30, 2022 •440 likes •819 views

A02 T. Kishimoto Osaka University CANDLES Collaboration Osaka University, Graduate school of science Masoumeh Shokati Temuge Batpurev Ken Lee Keong Bui Tuan Khai

  1. A02 T. Kishimoto Osaka University CANDLES Collaboration Osaka University, Graduate school of science 吉田斉、 Masoumeh Shokati 、李暁龍、 Temuge Batpurev 、 Ken Lee Keong 、芥川一樹、 Bui Tuan Khai 、 佐藤勇吾、水越彗太、山本康平、宮本幸一郎 Osaka University, RCNP 梅原さおり、能町正治、岸本忠史、竹本康浩、松岡健次、瀧平勇吉、鉄野高之介 Fukui University 玉川洋一、小川泉、中島恭平、戸澤理詞、清水慧悟、清水健生、森勇太、池山佑太、小沢健太、松岡耕平 Tokushima University 伏見賢一 Osaka Sangyo University 硲隆太、中谷伸雄、 Noithong Pannipa 、田坪博貴 Tsukuba University 飯田崇史 Saga University 大隅秀晃 The Wakasa wan Energy Research Center 鈴木耕拓 1 Sendai2019/3/7

  2. Why 48 Ca Q value (MeV) • Highest Q value – 4.27 MeV, ( 150 Nd: 3.3 MeV) – Least BG （ g : 2.6 MeV, b : 3.3 MeV ） – Large phase space factor • Small natural abundance: __ – 0.187% – Separated isotope → expensive • Next generation Natural abundance (%) – <m n >~ T -1/2 ~ M -1/2 (no BG) M: mass ~ M -1/4 （ BG limited ） CANDLES – Enrichment: mass ＋ S/N ： 500 times – High resolution ： bolometer （ crystal ） • Beyond inverted hierarchy Nuclear matrix element – 48 Ca + enrichment + bolometer → neutrino mass 2 Sendai2019/3/7

  3. CANDLES III ＠ Kamioka CANDLES III Kamioka Lab. Map Site: Kamioka U.G.L. ~1000 m Size: 3mΦ × 4mh (water tank) KamLAND Liquid scintillator Reservoir tank Lab D Purification system （ liq-liq ） Super Kamiokande CANDLES 4m 3m XMASS GDZOOKS! CANDLES III 3 Sendai2019/3/7

  4. CANDLES III(UG) CANDLES at Kamioka underground laboratory CANDLES III CaF 2 scintillator (CaF 2 (pure)) 305 kg (96 × 3.2kg) t ~ 1 m sec liquid scintillator (LS) 4π active veto 2m 3 t ~ a few 10nsec PMT’s 4m 13inch PMT × 48 CaF 2 20inch PMT × 14 light pipe Liquid scintillator light collection ： energy resolution light pipe water Veto PMTs Pulse shape difference CaF 2 (pure) : ～ 1 m sec Liquid scintillator : a few 10 nsec 4 Sendai2019/3/7 3m

  5. CANDLES III(UG) CANDLES at Kamioka underground laboratory CANDLES III CaF 2 scintillator (CaF 2 (pure)) 305 kg (96 × 3.2kg) t ~ 1 m sec CaF 2 (305kg) liquid scintillator (LS) 4π active veto 2m 3 Liquid scintillator t ~ a few 10nsec tank(2m 3 ) PMT’s PMT 13inch PMT × 48 Light pipe 20inch PMT × 14 light pipe light collection ： energy resolution Veto Pulse shape difference CaF 2 (pure) : ～ 1 m sec Liquid scintillator : a few 10 nsec 5 Sendai2019/3/7

  6. 4 p active veto by Liquid scintillator (LS) - Rejection of external g – ray background • Pulse shape information by 500 MHz Flash ADC. • Distinguish event type by offline pulse shape analysis taking advantage of different decay time. bb signal !? External g BG External g BG CaF 2 + CaF 2 Liquid Scintillator Liquid Scintillator (1 m sec) (~10nsec) b -ray Liquid g -ray Scintillator Liquid CaF CaF 2 Sendai2019/3/7 Scintillator Ca CaF 2 6 CaF 2 CaF

  7. Internal backgrounds and reduction • External BGs were reduced by LS active shild. Double pulse rejection • Remaining BGs originate from internal radioactivity of Th chain b+a decay ( 208 Tl and 212 Bi- 212 Po). Qvis=5.3MeV • 2 nbb is not serious BG in T 1/2 =300ns current sensitivity. (it will be major BG after 48 Ca enrichment) b+g decay Q=5MeV • We reject remaining BGs by analysis. Preceding a rejection 7 Sendai2019/3/7

  8. Rejection of Double Pulse Q a = 7.83MeV Q b = 3.27MeV b a 212 Po 208 Pb 212 Bi T 1/2 = 0.299 m sec 64% Q b = 2.25MeV Q a = 8.95MeV BG in Q bb region: Sum E E α (1/3 Quench) +E β ≃ 5.3 MeV Typical Pulse Shape 900ns 50ns Delayed Prompt Reduction D T > 30ns(3ch) ; ~5% 100MHz FADC (old) 500MHz FADC . . . D T > 10ns ; ~2% 8 Sendai2019/3/7

  9. 208 Tl event cut Th 系列 a b 212 Bi 208 Tl 208 Pb a - b 崩壊 232 Th T 1/2 = 60.6m T 1/2 = 3.05min stable Q a = 6.21MeV Q b = 5.00MeV Eneryg spectrum of prompt events 212Bi candidate Accidental event T½ = 178 ± 55sec 212Bi candidate-Accidental Delayed : 3.1-5MeV Time gate : ~180sec 1. Find parent 212 Bi a -decay candidate by pulse shape analysis. 2. Apply 12min veto from 212 Bi candidate in the same crystal. 9 Sendai2019/3/7

  10. External backgrounds -- Neutron source run --  To confirm our assumption that high E gamma ray BG’s are from (n, g ) reactions, 252 Cf neutron source was set on 2m the detector and data were taken. • Spectra for neutron source run and physics run are consistent. • MC simulation of (n, g ) can well reproduce the BG spectrum. We identified main BG as (n, g ) !! 10 Sendai2019/3/7 Neutron flux@Kamioka see K. Mizukoshi’s Poster

  11. Shield for (n, g ) background reduction CANDLES tank CANDLES shield overview Pb shield (7-12cm) Reduce g -ray from surrounding rock Effect of Pb (n, g ) is one order smaller than that of stainless tank Boron sheet (4-5mm) n Reduce n captured by stainless tank g • (n, g ) BGs in CANDLES is expected to become 1/80 by MC. • Expected number of backgrounds after shield installation: Rock : 0.34 ± 0.14 e .14 even vent/year ear Tank : 0.4 ± 0.2 .2 even vent/year ear 11 Sendai2019/3/7

  12. Pb shield construction • Pb shield construction was started from March 2015. • All the collaborators worked very hard! Side Pb shield Top Pb shield Bottom Pb shield 12 Sendai2019/3/7

  13. Position reconstruction and crystal selection • Position of each event is reconstructed by weighted mean of observed charge in each PMT. Crystal separation is ~7 s peak to peak. • Crystal selection criteria is within 3 s from the peak. • 27 clean crystals (Th contamination < 10 m Bq/kg) out of 96 • crystals are selected and the results are compared to all crystals. Th activity [ m Bq/kg] ± 3 s X axis [mm] 13 Sendai2019/3/7

  14. Energy Spectra & Event Selection LiveTime : 131 days 27 crystals ( 232 Th <10uBq/kg) 95 crystals Q β Q β β β Exp. Data 212 BiPo Cut LS Cut 208 Tl Cut # e eve vent 95 95 crys ystal als 27 c crys ystal als Q β 4-5MeV 5.5-6.5MeV Q β 4-5MeV 5.5-6.5MeV β β LS Cut 115 257 8 12 23 1 208 Tl Cut 19 49 6 3 6 1 10 34 6 0 2 1 Sendai2019/3/7 14 ☑ No event in high purity crystals is confirmed.

  15. Results PANIC2017 Exp. Data and BG MC In 27 CaF 2 95 C CaF aF 2 27 C CaF aF 2 Q β β Livetime 131 0 ν β β eff. 0.39 ± 0.06 Event in ROI 10 0 Expected BG ~11 ~1.2 >3.8x10 22 > 6.2x10 22 22 Sensitivity (yr) 6.2x10 22 3.6x10 22 22 χ 2 β <1.5, - 3σ<SI<1σ - 2σ<position cut<2σ Pileup cut > 20ns 208 Tl cut - 1σ<0ν β βwindow<2σ CANDLES is now giving the best lifetime limit! ・ further measurement Sendai2019/3/7 15 ・ developments for future

  16. 93 crystals 21 crystals ( 228 Th < 10 μBq/kg) Livetime 504 days Livetime 504 days Very Preliminary Very Preliminary BG from (n,γ) Statistics : 504 days The obtained spectra as expected from BG estimation We have ~ 300 days more statistics (not yet finished analysis) BG from (n,γ) is reduced by ~ 100 with shield installation. 0νββ analysis CaF 2 Crystal x 21 Replace crystals 228 Th contents within crystal < 10 μBq/kg All BG cuts are applied, but cut condition is not optimized yet. LS veto & β -events cut 212 Bi-Po sequential decay, 208 Tl veto after 212 Po-decay (18 min.) Sendai2019/3/7 16

  17. 48 Ca enrichment • Natural abundance of 48 Ca is 0.187%. • 48 Ca has a room of 500 times improvement (S & S/N) by enrichment • Commercial 48 Ca  too expensive (M$/10g but kg- ton) • Enrichment is crucial for large volume 48 Ca DBD search. • Challenges in CANDLES: – Crown ether resin + chromatography • 1.3 times – Crown ether + micro reactor – Laser separation – Multi-channel counter current electrophoresis (MCCCE) Sendai2019/3/7 17

  18. Laser Isotope Separation of 48 Ca Principle Experiment Absorption spectrum of Ca ionization deflection ionization deflection spatial distribution 48 Ca i.p. TOF meas. of ion meas. by TOF momentum photon hν 2 Single laser absorption Two lasers ・ deflection e.s. ・ selective excitation (CW, diode laser) (CW, diode laser) 48 Ca For TOF measurement ・ ionization ・ ionization photon （ pulse, dye laser ） （ pulse, YAG laser ） hν 1 isotope shift ： a few hundred MHz emission g.s laser line width ： <1 MHz (random) Ionization Method Deflection Method We confirmed the enrichment of 48 Ca in the deflected atomic beam Optimization of various parameters • Excitation laser 0.5� Optimization of laser power density power density 0� TOF spectra at 4.5mm from the center of original atomic beam Position of the • Ionization laser Ca イオン信号量 [mV] � collection plate will 40 Ca wavelength -0.5� be adjusted to the 40 Ca 40 Ca power same as 44 Ca optimal position (nat. × 11) -1� 48 Ca achieved 90% 48 Ca ion signal[V] ion signal[V] 44 Ca (nat. × 480) 44 Ca High concentration -1.5� diode+dye� Mid. Concentration 48 Ca Small duty factor dye� Continuous -2� pulse(10nsec, 10Hz) operation -2.5� Time[μs] Time[μs] 質量数 � For the future mass production… Development of collection system of 48 Ca We continue R&D of Increase atomic beam/laser power Deflection Method Optimization of various parameters Sendai2019/3/7 18 More details... see K. Matsuoka’s Poster

Recommend

More recommend