The ZEPLIN program Hanguo Wang, UCLA, Physics and Astronomy Stony Brook, May. 5, Status of ZEPLIN II 2.A possible ZEPLIN-IV design 3.Long term plan

Detector response to WIMPs and Background Radioactive background electron recoil Target Nuclei nuclear recoil WIMP or Neutron (I,S,Th) Background Discrimination Ionization Scintillation Phonon

e-e- Secondary (S2) Electroluminescence Primary (S1) Scintillation PMT LXe Gas liquid γ n-r e-e- PMT ZEPLIN II Design Principle PTFE

Recoil Event S1 S2

Drift and Luminescence Field Modeling Mesh Structure Main Drift Volume PMT

ZEPLIN II Detector ColdHead HV & signal Feedthrough Gas Xenon PMT Field Rings Liquid Xe Vacuum

Zep II Charge Extraction & Luminescence Field Grid 88% transparency

Wire mesh HV feedthrough & internal cable PTFE Baffle

ZEPLIN II Operation Underground at Boulby Mine, UK Detector fully operational Physics data taking in progress Data analysis in progress Lead Shield Purifier Safety Dump Neutron shield & Compton Veto

ZEPLIN II Electron Lifetime and Light Collection in Liquid Xenon 57 Co 103pe/122keV day Liquid purification well understood Greater than 1-ms electron lifetime typical 1.5 photoelectron/keV at zero field e-lifetime (µs)

P1 – Primary of Neutron S1 – Secondary of Neutron P2 – Primary of Gamma S2 – Secondary of Gamma P2 S2 S1 P1

3-D Event Display X Y Z Data from: z2_ Co

waveforms from ZEPLIN II 89% signal 4-sigma cut 3.2x10 -5 Log10(S2/S1) vs S1 Plot Background Discrimination Gamma S2 S1 AmBe Run & Dark Matter run Possible neutron double scatter overlap S2 Very clean waveform Excellent recoil discrimination from S2/S1

Summary of ZEPLIN II System Integration Status Cooling System Stable Slow Control System operational HV System, Feedthroughs complete Luminescence grid capable for 100% charge extraction good S2 gain DAQ system and Software Tested Liquid level monitoring with S2 pulse width and drift time Instrument tilt/grid shape monitor across whole surface with S2 Recirculation system to purify xenon continuously Routine two-phase operation established underground 9 hours to fill and 6 hours to empty Electron lifetime reach well above 1-ms Calibration and preliminary data runs started Performance Ionization yield from xenon nuclear recoil observed! Primary light yield as expected field) Excellent background discrimination

ZEPLIN II ZEPLIN IV/MAX ton ZEPLIN III 30kg 8kg ZEPLIN long term strategy I + =

Direct Scale-up Based on the ZEPLIN II/III 250kg 250kg fiducial mass Two phase xenon 50 5-inch-PMT 19 on bottom 31 on top 30-cm total drift length Light yield ~ 4pe/keV E=1.5kV/cm Xenon Purification Forced Circulation in liquid Active liquid recovery ~R x H = 0.5 (m) x 1.0 (m)

1-ton 5-ton ZEPLIN long term strategy II Towards ton-scale PMT-less detector CsI Nano-Tip Readout

Reverse operation of a cold-emission Type device to achieve charge gain in liquid near the tip Local high electric field for high gain 100 % primary charge collection Low absolute field with nano-structure

Active Xe Xe Self shield Vacuum HV CsI Coated CsI internal photo-cathode – 4-pi light collection (except shadow) 6 photo-electron/keV 1.6 ton fiducial, 5.8 ton total 28 cm xenon self shield Structurally sound Minimized field shaping structure (Less materials) Extremely low background Measure both scintillation and ionization (3-D events mapping) background rejection Compact design Cabling

VI Xe Target VII Xenon Purification and Safety System for ZEPLIN IV VI, VII, are vacuum pumps Active Xenon collection system will take less space (1.4 x linear size) Xenon purification in liquid phase (less cooling power) Manual Valve Cooling Pump Getter. Safety Dump Cooling Vacuum Insulated Line C.B. C.B. Control Box

ZEPLIN IV/MAX layout 1, Target Detector: (250kg  ton scale) 8m x 8m x 6m (WxLxH) Central detector, Active neutron and Compton veto Lead shield, Neutron Shield. 2, Electronic & Control: 5m x 4m x 3m DAQ system, Slow control, 3, Auxiliary systems: 8m x 8m x 4m Active xenon recovery system and related pipe-works and controls 4, Total Peak Power 25kW 5, Office

Current ZEPLIN II Collaboration Groups DB Cline, W.C. Ooi, F Sergiampietri (a), H Wang, P Smith (b), X Yang Physics and Astronomy, UCLA, (a) Pisa, (b) RAL&UCLA JT White, J Gao, J. Maxin, G. Salinas, R. Bissit, J. Miller, J. Seifert Department of Physics, Texas A&M University T Ferbel, U Schroeder (Chemistry), F Wolfs, W Skulski, J Toke Department of physics and Astronomy, Rochester University Y Gao Southern Methodist University, Texas GJ Alner, C Bungau, B Camanzi, TJ Durkin,, R Luscher JD Lewin, RM Preece, NJT Smith, PF Smith Particle Physics Department, Rutherford Appleton Laboratory, Chilton, Oxon H Araujo, A Bewick, D Davidge, JV Dawson, AS Howard, WG Jones, MK Joshi, V Lebedenko, I Liubarsky, T J Sumner, J J Quenby, R Walker Blackett Laboratory, Imperial College of Science, Technology and Medicine, London MJ Carson, E Daw, J Davis, T Gamble, VA Kudryavtsev, TB Lawson, PK Lightfoot, JE McMillan, B Morgan, SM Paling, M Robinson, NJC Spooner, DR Tovey Department of Physics and Astronomy, University of Sheffield A. S. Murphy, C Ghag University of Edinburgh, Department of Nuclear Physics M. Danilov, D Akimov, A. Kovalenko, V. Stekhanov ITEP, Moscow, A. Policarpo, I. Lopes, V. Chepel LIP-Coimbra