Double Beta Decay: Scintillators Mark Chen Queen’s University Neutrino 2008 Christchurch, New Zealand May 28, 2008 1
Talk Outline � scintillators for double beta decay: � what they can offer � survey of experimental programs � XMASS double beta decay [liquid xenon] � ELEGANT / CANDLES [inorganic crystals] � Kiev group [inorganic crystals] � SNO+ double beta decay [loaded liquid] � summary May 28, 2008 M. Chen 2 Neutrino 2008
Why Good Energy Resolution is Needed? � to separate 0 νββ from 2 νββ � to separate 0 νββ signal from other gamma lines from S. Elliott and P. Vogel from H.V. Klapdor-Kleingrothaus et al. May 28, 2008 M. Chen 3 Neutrino 2008
Can You Live With Worse Resolution? � to separate 0 νββ from 2 νββ � YES! by fitting the endpoint shape…resolution is far less important when fitting spectral shapes than simply counting signal and background events in an energy bin � this is already done (e.g. NEMO-3) 100 Mo � to separate 0 νββ signal from other gamma lines � YES! if there are no backgrounds! � how to achieve zero (low) γ background? � use B-field tracking detector: tags β − β − from γ ’s or � choose a high Q-value isotope � with an ultra-low background detector from F. Piquemal May 28, 2008 M. Chen 4 Neutrino 2008
Above the 208 Tl Line at 2.614 MeV highest energy line from natural radioactivity continuum background from internal Th chain contamination typical Ge spectrum from Ph. Hubert continuum background from internal U chain (radon) contamination ends at 3.2 MeV if you are searching for a peak, you can live with a low-level continuum background May 28, 2008 M. Chen 5 Neutrino 2008
ββ Isotopes with High Q-values isotope Q-value natural abundance [MeV] 48 Ca 4.27 0.19% 150 Nd 3.37 5.6% 96 Zr 3.35 2.8% 100 Mo 3.03 9.6% 82 Se 3.00 9.2% 116 Cd 2.80 7.5% May 28, 2008 M. Chen 6 Neutrino 2008
What Do Scintillators Offer? � “economical” way to build a detector with a large amount of isotope � several isotopes can be made into (or put in) a scintillator � ultra-low background environment can be achieved (e.g. phototubes stand off from the scintillator, self-shielding of fiducial volume) � with a liquid scintillator, possibility to purify in-situ to further reduce backgrounds May 28, 2008 M. Chen 7 Neutrino 2008
Experimental Programs – I � XMASS double beta decay � liquid xenon scintillation � 136 Xe, Q-value = 2.48 MeV � slides from S. Moriyama May 28, 2008 M. Chen 8 Neutrino 2008
Strategy of the XMASS project BG reduction with self shield is ~30cm ~1m effective < 500keV ~1 ton detector ~2.5m (FV 100kg) Dark matter search ~20 ton detector Prototype detector Under construction (FV 10ton) (FV 3kg) Solar neutrinos Dark matter search Confirmation of feasibilities of Double beta decay option the ~1ton detector w/ different design to realize low background at ~MeV.
XMASS: 136 Xe double beta decay • One possible method utilizes a high pressure liquid-xenon detector under room temperature. R&D ongoing. Mirror Acrylic vessel Water shield ΔΩ >90% Liquid xenon Wavelength Scintillation light ~5MPa, room temp. shifter 1yr, 10kg measurement 1.5 x 10 25 yr � <m ν >=0.2~0.3eV Acrylic vessel PMT RI contamination in the acrylic vessel (~10 -12 g/gU) limits its sensitivity. • Photon yield at room temp. ~29 photons/keV (K. Ueshima et al., arXiv0803.2888) • Energy resolution needs to be evaluated.
Photon yield measurement at room temp./ w avelength shifter/elliptic w ater tank High pressure chamber PMT ~29photons/keV arXiv0803.2888 Elliptic tank D.N.Mckinsey et.al. NIMB 132 (1997) 351 0.5% TPB doped PS, 100 μ m � Three components were developed. Under examination.
Experimental Programs – II � Osaka group: slides from T. Kishimoto and S. Umehara � past: ELEGANT VI � CaF 2 (Eu) scintillating crystals � 7.7 g of 48 Ca, Q-value = 4.27 MeV � ran at Oto Cosmo Observatory � future: CANDLES III � pure CaF 2 scintillating crystals � U chain: ~36 μ Bq/kg (30 times better than ELEGANT VI) � Th chain: ~29 μ Bq/kg (3 times better than ELEGANT VI) � ~300 kg of crystals (that’s ~400-450 g of 48 Ca) � expected resolution: ~3.5% FWHM at endpoint � will run in Kamioka May 28, 2008 M. Chen 12 Neutrino 2008
ELEGANT VI � 23 CaF 2 modules ~3.5 kg 19 F ~7.7 g 48 Ca � Background reduction � least material : non hygroscopic � 4 π active shield � CaF 2 (Eu)+CaF 2 (pure) roll-off ratio � segmentation � CsI(Tl) veto detector � passive shield � OFHC Cu(t:5 cm), Pb(t:10 cm) � air-tight box + N 2 gas purge Rn in the air � LiH + paraffin(t:15 mm), Cd sheet(t:0.6 mm), and H 3 BO 3 +H 2 O tank neutron Surrounded by H 3 BO 3 loaded-water tank at Oto Cosmo Observatory
ELEGANT VI Scintillators in ELEGANT VI System CaF 2 Module PMT PMT CaF 2 (Eu) CaF 2 (pure) . . . UV Light . . . Visible Light CsI(Tl) CaF 2 Module Active Shielding Technique in ELEGANT VI system
Double beta decay of 48 Ca Double beta decay of 48 Ca COUNTS(/40keV) Preliminary Experimental Data Date Analysi Number Expected Detection Live 10 2 212 Bi(Sim) s of Event Efficiency Time BG( 212 Bi, kg ・ day 214 Bi, 208 Tl) Jun without 0 1.30 0.55 1553 10 1998 - FADC Q ββ of 48 Ca Jan with 0 0.27 0.53 1114 2003 - FADC 1 Jan with 0 0.43 0.53 2280 2004 - FADC -1 208 Tl(Sim) 10 0 νββ Half ‐ Life of 48 Ca : -2 10 > 6 × 10 22 year (90% C.L.) 3000 3250 3500 3750 4000 4250 4500 4750 5000 Energy(keV) Preliminary Next step: CANDLES 15
CANDLES CAlcium fluoride for studies of Neutrino and Dark matters by Low Energy Spectrometer • undoped CaF 2 (CaF 2 (pure)) – 48 Ca (0.187%) CaF 2 crystal Water Buffer + w.l. shifter – 305 kg (III-chika) ~0.1 eV 3.4 t (IV) 30 t, 2% enriched (V) ~30 meV (best NME) • Liquid Scintillator (LS) – 4 π active shield liquid scintillator – also wavelength shifts light • Photomultiplier – large photo-coverage 17" PMT • Water buffer 16 CANDLES Collaboration – Passive shield
Two-Layer Wavelength Shifter Concept of Method � WLS Phase M.O.(100%)+PPO(0.3g/L) � 5-10 mm in thickness � � large conversion efficiency � Veto Phase CaF 2 (Pure) M.O.(80%)+PC(20%)+PPO(1.0g/L) � � large light output May 28, 2008 M. Chen 17 Neutrino 2008
CANDLES III CaF 2 : 191 kg 10 3 cm 3 × 60 Position reconstruction in X-Y plane 40 PMTs Tank: Φ 2.8 × h 2.6 m
CANDLES III Status � ICRR completed the excavation of two new chambers in Kamioka (one for XMASS and one for CANDLES) � new space ready for occupancy at the end of this year � ~300 kg of crystal will be installed in detector � <m ν > < 0.5 eV � data taking starts in 2009 � also in the process of requesting funding to enlarge for the future May 28, 2008 M. Chen 19 Neutrino 2008
Experimental Programs – III � Kiev group: slides from F. Danevich � experiments developed and/or considered in the past with different scintillating crystals with different isotopes � e.g. CAMEO, CARVEL, etc. � possible deployment of crystals in large, existing detectors (e.g. Borexino, SNO) � currently the following scintillating crystals (and experiments) are being developed � 116 CdWO 4 with 116 Cd, Q-value= 2.80 MeV � also 106 Cd β + β + decay, Q-value = 2.77 MeV � CaMO 4 with 100 Mo, Q-value = 3.03 MeV � ZnWO 4 with 64 Zn, Q-value = 1.10 MeV May 28, 2008 M. Chen 20 Neutrino 2008
Kyiv Institute for Nuclear Research, Kyiv Institute for Nuclear Research, Solotvina Underground Laboratory (Ukraine) Solotvina Underground Laboratory (Ukraine) Present projects Present projects Main results R&D of advanced 116 Cd 2 β • β decay of 2 β experiment (producing of ~1.2-1.8 116 Cd decay of 116 Cd 2 kg 116 CdWO 4 crystal scintillators) ν = 19 yr 2.9 ×10 ×10 19 2 ν in collaboration with ITEP T 1/2 2 = 2.9 yr T 1/2 (Moscow, Russia), KIMS (Korea), ν ≥ 23 yr ≥ 1.7 ×10 23 1.7 ×10 0 ν T 1/2 0 yr @ 90% CL @ 90% CL T NIIC (Novosibirsk, Russia) 1/2 〈 m 〈 ν 〉 〉 ≤ ≤ 1. m ν 1.7 7 eV eV Search for 2 β of Zinc and • Tungsten by ZnWO 4 in [PRC 68 (2003) 035501] collaboration with DAMA (experiments are running in the β decay LNGS, Italy) 2 β Search for 160 160 Gd Gd 2 decay Search for ν ≥ • CaMoO 4 crystal scintillators for 21 yr ≥ 1.3 ×10 21 1.3 ×10 0 ν T 1/2 0 yr T 2 β decay of 100 Mo [large 1/2 collaboration, see NIMA 584 [NPA 694 (2001) 375] (2008) 334 ] First experiment to search for R&D of ≈ 0.15 kg 106 CdWO 4 in First experiment to search for • β of collaboration with DAMA (Italy), 2 β 64 Zn by using ZnWO of 64 Zn by using ZnWO 4 2 4 JINR (Dubna, Russia) crystal producers in Ukraine and Russia [NIMA 544 (2005) 553] 21
CaMoO 4 crystal scintillators CaMoO 4 crystal scintillators β decay of 2 β decay of 100 100 Mo Mo 2 CARAT, Lviv, Ukraine Energy resolution FWHM=10.3% for 662 keV γ line of 137 Cs was obtained with CaMoO 4 crystal scintillators ICMSAI, Moscow, Russia produced by CARAT NIMA 584 (2008) 334 22
Recommend
More recommend
