ZEPLIN II Status & ZEPLIN IV Muzaffer Atac David Cline Youngho Seo Franco Sergiampietri Hanguo Wang ULCA ZonEd Proportional scintillation in LIquid Noble gases ZEPLIN Collaboration -- UKDM-UCLA-Italy Acknowledgement: Roy Preece Nigel Smith Peter Smith RAL, UK Pio Picchi Frascati

July 7, 2001H. WANG, ZEPLIN II, UCLA2 ZEPLIN Construction Status Engineering design completed (Central detector), Materials for key parts already arrived, And machining already start at UCLA, All other material orders are placed, Copper cast will be ordered after thermal, mechanical, vacuum and pressure evaluation, First assembly at UCLA this fall, The overall design is very cost effective.

July 7, 2001H. WANG, ZEPLIN II, UCLA3 Xenon discriminating detector Available in Large Quantities High Atomic Number (Z Xe =54,  WIMP-Nucleon  A 2 ) High Density (~ 3g/cm 3 liquid ) High Light (175nm) & Ionization Yield Can be Highly Purified long light attenuation length (~m) long free electron life time (~5ms) Gamma & Recoil signal Discrimination Easy to Scale up to Large Volume No Long Lived Radioactive Isotopes

July 7, 2001H. WANG, ZEPLIN II, UCLA4 Liquid Xenon Scintillation Mechanism Very good for pulse shape discrimination due to decay profile difference between nuclear recoil & electron recoil Very good background rejection due to (E i /E s ) M.I.P. >> (E i /E s ) H.I.P.

July 7, 2001H. WANG, ZEPLIN II, UCLA5 Principle Tests Setup 1.Ceramic 2.Quartz Window 3.Stainless steel Cathode 4.Source 5.Grounded Grid 6.Anode wire frame NIM A327 (1993) 203

July 7, 2001H. WANG, ZEPLIN II, UCLA6 Primary & Secondary Scintillation vs field Alpha Gamma

July 7, 2001H. WANG, ZEPLIN II, UCLA7 Xenon Two-Phase Prototype Detector Primary- Scintillation Electro- luminescence  recoil

July 7, 2001H. WANG, ZEPLIN II, UCLA8 Proportional scintillation vs field Single phase 99.8% rejection P S P S

July 7, 2001H. WANG, ZEPLIN II, UCLA9 Background and recoil separation 200keV Heavy Ionization (recoil signal) Minimum Ionization (backgrounds) Primary Scintillation Secondary Scintillation Gamma recoil

July 7, 2001H. WANG, ZEPLIN II, UCLA10 Electron drift velocity in LXe

July 7, 2001H. WANG, ZEPLIN II, UCLA11 Details of ZEPLIN II 1.Fiducially volume: 40kg. 2.Two wire-frames provide both: electron extraction field Electro-luminescence field 3.Pure copper rings shapes the electron drift-field in liquid. 4.-HV applies to bottom plate to have high field for ionization electron extraction in liquid. 5.Extreme care taken to avoid HV discharge in gas. 6.Seven custom made PMTs for use in liquid xenon temperature 7.Custom made surface-mount resister-dividers for PMTs for use in gas xenon. 8.Dead region less than 0.1%

July 7, 2001H. WANG, ZEPLIN II, UCLA12 Construction in Progress Field shaping rings will be made out of pure Oxygen free copper The largest PTFE piece is being machined at the UCLA Physics department machine shop

July 7, 2001H. WANG, ZEPLIN II, UCLA13 ZEPLIN II system Setup Lead Shielding The central detector Active Veto Liquid xenon target Copper cast vacuum and target vessel

July 7, 2001H. WANG, ZEPLIN II, UCLA14 One Ton Scale-up based on the ZEPLIN II Design Total mass: one ton, 5 inch PMTs: 80 Copper cast vessels, Signal amplification using CsI internal photo-cathode, Signal cable, HV cable, Cooling system, Vacuum, and Xenon port

July 7, 2001H. WANG, ZEPLIN II, UCLA15 ANSYS finite element analysis for field configurations

July 7, 2001H. WANG, ZEPLIN II, UCLA16 CsI test results H-2  s V-20mV (E. Aprile et al., NIM A , )

July 7, 2001H. WANG, ZEPLIN II, UCLA17 Expected limit for ZEPLIN II and ZEPLIN IV

July 7, 2001H. WANG, ZEPLIN II, UCLA18 Conclusion High A number makes it match better the high mass WIMPs and yields high event rates. (    2) High scintillation and ionization yield makes it easy to achieve the following: Low energy threshold: less than 10keV (true recoil energy). Gamma and nuclear recoil discrimination by a factor of at least High liquid temperature and high density allows compact design and easy engineering solutions. Future development on CsI internal photo-cathode may reduce the background further (not discussed here). the 40kg ZEPLIN II detector running for a year may cover completely the DAMA region. The ZEPLIN IV future one ton detector will cover most of the SUSY region