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Satoshi SUZUKI Waseda University

Present status and perspective of cryogenic liquid detectors. Satoshi SUZUKI Waseda University. 13/Mar./2006 Cryodet @ Gran Sasso. Recent Development of Cryogenic liquid detectors. ICARUS. Pioneer of LAr TPC. NuMI T2K LXe TPC. Technology of LAr TPC was established by ICARUS.

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Satoshi SUZUKI Waseda University

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  1. Present status and perspective of cryogenic liquid detectors Satoshi SUZUKI Waseda University 13/Mar./2006 Cryodet @ Gran Sasso

  2. Recent Development of Cryogenic liquid detectors ICARUS Pioneer of LAr TPC NuMI T2K LXe TPC Technology of LAr TPC was established by ICARUS. Enlargement : 1kg---several steps---300ton(600ton)-〜10kton(final) MEG First big LXe detector form eg experiment Energy resolution Timing resolution Position resolution Demonstrate the potential of LXe detector XMASS Simple scintillation detector Self Shielding CLEAN(LNe) The biggest LXe detector for DM and pp 7Be solar n DAMA(LXe) ZEPLIN I XMASS Ⅱ ZEPLIN Ⅱ〜Ⅳ XENON WALP(LAr) Double Phase Detector DM search

  3. Signal Eg = mm/2 = 52.8MeV Ee = mm/2 = 52.8MeV q = 180o Time coincidence g m e MEG Experiment Expected sensitivity 〜 order of 10-14 (present limit = 1.2x10-11)

  4. Large light output yield • Wph(1MeV e) = 22.4eV • Pile-up event rejection • Fast response and short decay time • Uniform Liquid Xe scintillation

  5. MEG Xenon Detector • Active volume ~800l is surrounded PMTs on all faces • ~850PMTs in the liquid • No segmentation • Energy • All PMT outputs • Position • PMTs on the inner face • Timing • Averaging of signal arrival time of selected PMTs

  6. Large Prototype • 70 liter active volume (120 liter LXe in use) • 238PMTs immersed in LXe • Large enough to contain 50MeV g event(17X0) • Performance test using • 10, 20, 40MeV Compton g beam • 60MeV Electron beam • g from p0 decay

  7. Energy Resolutions 55 MeV 83 MeV to Xe 55 MeV to Xe Exenon[nph] 83 MeV

  8. Energy Resolution vs Energy PSI 2004 TERAS 2003 alpha Right  is a nice function of gamma energy

  9. Examples of Reconstruction (40 MeV gamma beam w/ 1 mm collimator)

  10. Absolute timing, Xe-LYSO analysis high gain normal gain 103 psec 110 psec 55 MeV Normal gain High gain A few cm in Z

  11. Liquid phase circulation system Absorption length > 5m in 10hours 1 m 2.5 m 5 m

  12. PMT DevelopmentSummary

  13. Self-shielding for low energy events Fiducial volume liquid Xe Volume for shielding Fiducial volume BG normalized by mass PMTs 6 orders of magnitude reduction for gamma rays below 500keV

  14. Isotope separation Abundance of natural Xe bb nucleon 124Xe 126Xe 128Xe 129Xe130Xe 131Xe132Xe 134Xe 136Xe (0.10%) (0.09% ) (1.92%) (26.4%) (4.07%) (21.2%) (26.9%) (10.4%) (8.87%) Even enriched Odd enriched Separate here Dark Matter Ⅱ Spin dependent Dark Matter Ⅰ 2nbb/0nbb Solar neutrino

  15. 10 ton detector Strategy of the scale-up 800kg detector 100kg Prototype ～30cm ～80cm R&D ～2.5m Dark matter search We are here Multipurpose detector (solar neutrino, bb …)

  16. 54 2-inch low BG PMTs Hamamatsu R8778 16% photo- coverage Liq. Xe (31cm)3 MgF2 window 100 kg prototype detector In the Kamioka Mine (near the Super-K) 2,700 m.w.e. OFHC cubic chamber Gamma ray shield

  17. hole C hole A hole B DATA MC Performance of the vertex reconstruction Collimated g ray source run from 3 holes (137Cs, 662keV) + + + C A B → Vertex reconstruction works well

  18. All volume 20cm FV 10cm FV Performance of the energy reconstruction Collimated g ray source run from center hole 137Cs, 662keV s=65keV@peak (s/E ~ 10%) Similar peak position in each fiducial. No position bias → Energy reconstruction works well

  19. Total 840 hex PMTs immersed into liq. Xe • 70% photo-coverage • Radius to inner face ~43cm 800kg detector • A tentative design (not final one) 12 pentagons / pentakisdodecahedron Eth = 5 keVee~25 p.e. This geometry has been coded in a Geant 4 based simulator

  20. Hamamatsu R8778MOD(hex) • Hexagonal quartz window • Effective area: f50mm (min) • QE <~25 % (target) • Aiming for 1/10 lower background than R8778 5.8cm (edge to edge) 0.3cm (rim) c.f. R8778 U 1.8±0.2x10-2 Bq Th 6.9±1.3x10-3 Bq 40K 1.4±0.2x10-1 Bq 5.4cm • Prototype has been manufactured already • Now, being tested 12cm

  21. Kr contamination • 85Kr makes BG in low energy region Target = Xe 102 cpd/kg/keV Kr 0.1ppm 1 10-2 DM signal (10-6 pb, 50GeV, 100 GeV) 10-4 10-6 • Kr can easily mix with Xe because both Kr and Xe are rare gas 0 200 400 600 800 energy (keV) • Commercial Xe contains a few ppb Kr

  22. Xe purification system • Processing speed : 0.6 kg / hour • Design factor : 1/1000 Kr / 1 pass • Purified Xe : Off gas = 99:1 Lower ~3m Raw Xe: ~3 ppb Kr (178K) Off gas Xe: 330±100 ppb Kr (measured) ~1% Purified Xe: 3.3±1.1 ppt Kr (measured) Higher ~99% Operation@2atm (180K)

  23. Summary of BG measurement Now (prototype detector) Goal (800kg detector) • g ray BG ~ 10-2 cpd/kg/keV → Increase volume for self shielding → Decrease radioactive impurities in PMTs (~1/10) • 238U = (33±7)×10-14 g/g → Remove by filter • 232Th < 23×10-14 g/g (90% C.L.) → Remove by filter (Only upper limit) • Kr = 3.3±1.1 ppt → Achieve by 2 purification pass 1/100 10-4 cpd/kg/keV 1/33 1×10-14 g/g 1/12 2×10-14 g/g 1/3 1 ppt Very near to the target level!

  24. W- phase Xe Detector (Direct & proportional scintillation ) Gas ~1μsec anode S2 Drift Time grid e- Ｅ Liquid ~40 nsec S1 cathode

  25. Signal from Double Phase Xe 42000photon/MeV Decay time 45nsec direct direct direct proportional drift time drift time proportional

  26. Recoil /γ ray Separation >99% γ ray rejection Proportional scintillation(S2) 22 keV gamma ray Recoil Xenon (neutron source) Direct scintillation(S1)

  27. Gas Xe 15 kg Double Phase Xe Detector grid Liquid Surface anode grid Gas Xe MgF2(cathode) 220mm OFHC Ed Liq Xe PTFE (Field shaping ring) 165mm PMT (HAMAMATSU R8778 x 7) MgF2(cathode) 160mm

  28. 15kg Chamber Construction Anode - Grid Set PTFE Field Shaping Ring PMT MgF2 Window (Cathode:gold coated mesh)

  29. 15 kg Chamber Construction Shield

  30. 3D-double phase xenon detector If we have pure xenon which is free from radioactive impurities, proportional scintillation is very useful. Multi-purpose detector WIMPs 136Xe double b decay pp 7Be solar n

  31. 3D W-phase test chamber Recirculation purification Circulation pump Getter • PMT: Hamamatsu R5900-06MOD • 1inch square type • QE=5% • Work in LXe Gas Xe Liquid Xe

  32. Position resolution(x,y) • Simulation • (for 100 keV electron) • Distance between PMT and anode: 3 cm • proportional scintillation • :1 mm Gaussian • Collection of electrons :80% • PMT Coverage : 20% • QE : 5％ 1ph/e 1000ph/e 103 104 105 106 107 • σxy < 1 mm will be possible by good adjustment of PMTs • Use multi -anode PMTs for double b decay experiment

  33. Proportional scintillation Energy spectrum for low energy g rays Low energy threshold for pp 7Be solarn < few keV 5.9 keV g ray from 55Fe 22 keV g ray from 107Cd • Independent of detector size

  34. g ray rejection for 0nbb decay experiment S1 one signal S2 more than two Compton scattering events ΔZ ~ few 100 mm

  35. Low energy detection by 3D-double phase detector in Underground Shielding Detector Low background environments WIMPs 0nbb decay pp, 7Be solar n low Eth <10 keV large mass particle ID energy resolution γ/βID low Eth huge mass 〜10 ton real time self-shielding particle ID (WIMPs, neutrons,)

  36. What is the most important in the future? How to collect photon effectively? Small detector Maybe yes Improve photon detector, PMT … Big detector No The best is to find a wave length shifter.

  37. Attenuation length vs Wavelength(l) T. Ypsilantis et al.(‘95) Rayleigh scattering ∝ 1/l4

  38. Light collection efficiency λ= 175 nm 15 kg W-phase detector Reflectance for PTFE：0.90 Absorption length of LXe：1 m Scattering length：40 cm 15.3 % 1.75 pe/keV (QE:25%) λ= 350 nm Reflectance for PTFE：〜 0.99 Absorption length of LXe：〜 20 m Scattering length：〜 3m 〜 80 % 〜 8 pe/keV MgF2：1.45 Refractancequartz：1.56 LXe ： 1.60

  39. TEA doped rare gas experiment Emission from TEA Ar* + Ar + Ar → Ar2* + Ar Ar2* → Ar + Ar + hn(VUV) Competitive process hn(VUV) + TEA → TEA* Ar2* + TEA → Ar + Ar + TEA* hn(VUV) + TEA → TEA+ + e Ar2* + TEA → Ar + Ar + TEA+ + e M.SUZUKI et al. (1987)

  40. Is it possible to apply to liquid? LAr Photo ionization effect was observed for both liquid. hn(VUV) + TEA → TEA+ + e (Ar2* + TEA → Ar + Ar + TEA+ + e) QE = 0.23 LXe hn(VUV) + TEA → TEA+ + e (Xe2* + TEA → Xe + Xe + TEA+ + e) QE 〜 1 Nobody check visible(UV) light! Excitation process should be occurred. Especially to LAr because of small QE.

  41. The end

  42. Rn assay with prototype detector • 238U series • 222Rn(t1/2 = 3.8d, 3.3MeV beta), … • 232Th series • 220Rn(55s, 2.3MeV beta[64%]), … 214Bi214Po210Pb b (Emax=3.3MeV)a (7.7MeV) t1/2 =164msec Observed coincident events 212Bi212Po208Pb b (Emax=2.3MeV) a (8.8MeV) t1/2 =299nsec (BR=64%) No candidate found

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