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1 ton Xe? - a Boulby View

1 ton Xe? - a Boulby View. How the Boulby Collaboration see development of a 1 ton Xe experiment. Our Strategy. Progress on the ZEPLIN I detector. Prospects for PMT avoidance. Why 1 ton Xe? - Boulby View. Objective. To reach “bottom” of neutralino space

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1 ton Xe? - a Boulby View

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  1. 1 ton Xe? - a Boulby View How the Boulby Collaboration see development of a 1 ton Xe experiment Our Strategy Progress on the ZEPLIN I detector Prospects for PMT avoidance

  2. Why 1 ton Xe? - Boulby View Objective • To reach “bottom” of neutralino space • Needs about 1 ton just to get sufficient recoil counts (a few hundred per yr) 1000 excluded 10 SUSY (mSugra) models have minimum sp ~10-10 pb (SI) probably excluded by accelerators events per kg per day 0.1 theoretically plausible 0.001 mass region 1 1000 100 10 WIMP mass (proton masses) case never so strong as now

  3. Why Xe? Motivation for Xe within the Boulby Programme • High-A target (Xe~130) for WIMP masses 50-500 GeV/c2 to reach 0.01/kg/d, and ultimately 0.0001 kg/d --> Complements NaI low-A, q(A) > 0.2 • Powerful discrimination (typically x100 better than NaI) with different techniques and geometry possible --> satisfies basic requirement for: (i) recoil identification (ii) diagnostic array capability • Big scale-up potential (yet retains recoil identification) --> experience of ICARUS, UCLA, Suzuki, Aprile, • Lower cost than alternatives? (low temperature, Ge..) • Prospects for isotopic enrichment better than Ge…...

  4. three discrimination techniques + Xe Ionisation +Xe Nuclear/Electron Recoil (1) scintillation pulse shape + Xe 2 Excitation - +e (2) ionisation-scintillation - low field- (recombination) * ** Xe Xe + Xe +Xe (3) ionisation-scintillation - high field, low threshold - * Xe 2 175nm 175nm Triplet Singlet single phase Xe two phase Xe 3ns 27ns gas 2Xe 2Xe liquid liquid World expertise • ICARUS-UCLA • Doke group (Japan) • DAMA • Columbia • UKDMC • ITEP XENON (PSD and Scint/Ion)

  5. basic ionisation-scintillation and high target mass - improve by x10 - UCLA concept demonstrate basic discrimination with PSD - set first limits ionisation-scintillation and high field - ultimate discrimination, low threshold - Boulby Collaboration Strategy A multinational programme ZEPLIN-MAX ion-scint two phase Xe 1000 kg ZEPLIN-II ion-scint two phase Xe 30 kg running ZEPLIN-I single phase PSD 4 kg ZEPLIN array under construction ZEPLIN-III Ion-scint two phase Xe high field 6 kg new (5 years) : Involved in programmes: UCLA, CERN/Padova, Torino, ITEP, Coimbra, Columbia, RAL, ICSTM, Sheffield

  6. Towards a 1 Ton design ZEPLIN array as a test bed • The Zeplin I, II, III array is a test bed for the scale-up --> solve basic underground operation problems --> understand mechanical, shielding and low background material issues --> understand discrimination issues: high field, low field --> what should it be called!? ZEPLIN-MAX, ZEPLIN IV….! Scale-up options • Several concepts are being explored (I) a single vessel of 1 ton (2) modular at level of about 80 kg: identical modules or different (3) larger modules of ~250 kg: identical modules or different (4) combination of high threshold and low threshold (5) removal of PMTs

  7. Some Tasks for 1 Ton • Engineering interfaces • -------------------- • Purification system • Xenon recovery system • High voltage systems • Scintillator handling system • Infrastructure Requirements • -------------------------- • Power and heat budget • Boulby facility requirements • - castle design, LN2 plant • Equipment spares • Health and Safety • Risk assessment and control • Sequencing • ---------- • Commissioning sequence • Required calibration test sequence • Transportation sequence • Installation sequence • Data Handling • ------------ • Data acquisition requirements and solutions • Data pipeline

  8. ZEPLIN I,I,III - 2001/2 complete and run the full ZEPLIN array • ZEPLIN I already running -->some upgrading of PMTs • ZEPLIN II under construction (with collaborators) -->installation, shielding, daq -->start running • ZEPLIN III under construction (with collaborators) -->installation, maintenance -->start running RESULT: (a) attain 0.01/kg/d, (b) diagnostic array with complementary techniques

  9. 3 modules 4 sub- units shielding 80 kg target ZEPLIN - 1 ton Concept ZEPLIN-MAX A BDMC multinational programme • Final design by mid 2003 • Modular, high and low threshold • Construction 2004+ RESULT: (a) attain 0.0001/kg/d, (b) diagnostic array with complementary techniques

  10. 10-3 10-4 10-5 ZEPLIN 2002/3 10-6 ZEPLIN I/II 2003 CDMS II CRESST II 10-7 ZEPLIN II/III 2004 10-8 ZEPLIN-MAX 2006 10-9 10-10 10 100 1000 ZEPLIN-XENON Predictions NaI 1996 limit WIMP-nucleon cross-section, pb ZEPLIN predictions based on prototype tests and operation of ZEPLIN I WIMP mass GeV

  11. 3 modules 4 sub- units shielding 80 kg target ZEPLIN-MAX One Concept ZEPLIN-MAX (1 ton) (a multinational programme) RESULT: (a) attain 0.0001/kg/d, (b) diagnostic array with complementary techniques

  12. ZEPLIN-MAX ZEPLIN-II ZEPLIN-III ZEPLIN locations at Boulby Stub 2 JIF Facility ZEPLIN-I

  13. Xe+ +Xe Xe2+ +e- (recombination) Xe* Xe** + Xe +Xe Xe2* 175nm 175nm Triplet Singlet 3ns 27ns 2Xe 2Xe UKDMC Xenon - ZEPLIN I

  14. ZEPLIN I Underground Boulby stub 2 laboratory xenon purification Top of ZEPLIN I veto Counts vs. time Xe temp vs. time Pb shielding room temp vs. time Stable operation demonstrated

  15. ZEPLIN Operations at Boulby

  16. ZEPLIN I Laboratory tests • PMT background events rejected by turret fiducial cuts as expected 137Cs events origin is where all 3 PMTs record identical signals turret events rejected by asymmetry cut • Compton veto (1 ton PXE) found to have ~50 keV threshold

  17. 0 500 1000 1500 2000 0 20 40 60 80 100 ZEPLIN I Laboratory tests pe/keV 2 • Light collection exceeds design spec of 1 pe/keV Z I data 1 theory 0 keV tau (ns) • Up to 50% difference in neutron and gamma time constants 50 keV 0

  18. ZEPLIN I Laboratory tests • Light Yield • Increases at low energy • Spatial Uniformity • 137Cs Source Data Theory

  19. ZEPLIN I Discrimination Gamma source  (ns) n Neutron source (ns) 10-20keV 20-30keV

  20. ZEPLIN I - Predicted Limits

  21. ZEPLIN I - Results Predictions for 1 year 85Kr < 10-17 atoms/atom

  22. CsI photocathodes in LXe: E.Aprile, NIMA 338 (1994), 328; NIMA 343 (1994), 121. GEM phototubes in noble gases:http://gdd.web.cern.ch/GDD/A.Buzulutskov, NIMA, 443 (2000), 164. Xe Gas GEMs CsI He Cooling Liquid Xe PTFE Reflector Field Shaping Rings CsI nucl.rec. elec.rec. PMT Removal for Scale-Up? • Sheffield test cell

  23. GEM Prototype Target High or low field operation In-house CsI photocathode production GEMs of Sheffield design from CERN

  24. GEM Rig

  25. ZEPLIN II (UKDMC collaboration with US and Italy) ionisation-scintillation discrimination OFHC copper plate ~30kg Lxe detector shielding, integration, readout, daq UCLA, Torino, Padova UKDMC cooling rings PTFE cone • Completion due end 2001

  26. ZEPLIN III (UKDMC collaboration with US and Russia) ionisation-scintillation - low threshold • 6 kg liquid Xe • High field (20 kV) operation for better discrimination Xe 31 two-inch photomultipliers 1kg test chamber result • Completion due end 2001

  27. 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10 100 1000 UKDMC-BDMC Future NaI 1996 WIMP-nucleon cross-section, pb NAIAD/Xe 2002/3 Xe 2003/4 DRIFT 2004/5 Xe 2005 Xe-MAX 2006 WIMP mass GeV

  28. DAMA Xenon • Operating 6.5 kg Kr free (85Kr beta emitter) Liquid Xenon with PSD. • 99.5% enriched in 129Xe (spin-dependent couplings). • Viewed by three MgF2 PMTs through quartz windows (l=175 nm). • Measured quenching factor ~ 45% - 65%. • Stable operation at -105 oC. (see Nuovo Cim 19 (1996) 537)

  29. XENON - Kamioka (Scint/Ion) • Liquid-gas double phase xenon • 0.3l low background construction • 8 cm drift to proportional scintillation region • 99% background rejection for 10-100 keV • 3 months continuous operation • 1 kg experiment in Kamioka

  30. Possibilities • Ionisation - Germanium: GENIUS proposal for 1 or 10 tons Intrinsic low background but NO discrimination and expensive (mainly bb) • Scintillation - NaI: LIBRA (DAMA) 250 kg under construction Annual modulation (what if DAMA region ruled out), PSD not sensitive enough • Ionisation/thermal - CDMS?: Good discrimination but difficult technology and expensive • XENON - ZEPLIN-MAX proposal for 1 ton (UKDMC-BDMC, US, EU) Good discrimination, world expertise, simpler technology(?), less expensive • GAS - DRIFT-MAX proposal scale-up directional detector (UKDMC-BDMC, US) TOWARDS 1 TON? Motivation • To reach 10-10 pb

  31. - - - - - Current Direct Limits http://cdms.berkeley.edu/limitplots/ • Sensitivity ≈ 10-6 pb • DAMA: annual modulation of rate • CDMS: neutron background subtraction • UKDMC: ‘anomalous’ events preclude limit

  32. Summary WIMPs (10-9(or -12) pb < scp < 10-6 pb, 50 GeV < m <600 GeV) • DAMA NaI annual modulation as objective WIMP or fluctuating low energy noise? • UKDMC ‘anomalous events’ as surface alphas? Seen in Saclay (DAMA) crystal • CDMS recoil limit (almost) excludes DAMA Subtraction of neutron signal • Several detectors becoming sensitive at 10-6 pb • Many more direct searches underway to reach ≈10-8pb • Indirect n searches reaching sensitivities to exclude models

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