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 PreeceNigel SmithPeter SmithRAL, UK Pio Picchi

Frascati

July 7, 2001 H. WANG, ZEPLIN II, UCLA 2

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, 2001 H. WANG, ZEPLIN II, UCLA 3

Xenon discriminating detector

•Available in Large Quantities•High Atomic Number (ZXe=54, WIMP-Nucleon A2) •High Density (~ 3g/cm3 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, 2001 H. WANG, ZEPLIN II, UCLA 4

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 (Ei/Es)M.I.P.>> (Ei/Es)H.I.P.

July 7, 2001 H. WANG, ZEPLIN II, UCLA 5

Principle Tests Setup

1. Ceramic2. Quartz Window3. Stainless steel Cathode4. Source5. Grounded Grid 6. Anode wire frame

NIM A327 (1993) 203

July 7, 2001 H. WANG, ZEPLIN II, UCLA 6

Primary & Secondary Scintillation vs field

Alpha

Gamma

July 7, 2001 H. WANG, ZEPLIN II, UCLA 7

Xenon Two-Phase Prototype Detector

Primary-Scintillation

Electro-luminescence

recoil

July 7, 2001 H. WANG, ZEPLIN II, UCLA 8

Proportional scintillation vs field

Single phase 99.8% rejection

P S

P

S

July 7, 2001 H. WANG, ZEPLIN II, UCLA 9

Background and recoil separation

200keV1000Heavy Ionization(recoil signal)

Minimum Ionization(backgrounds)

Primary Scintillation

Seco

nd

ar y

Sci

nti

l lati

on

Gamma

recoil

July 7, 2001 H. WANG, ZEPLIN II, UCLA 10

Electron drift velocity in LXe

July 7, 2001 H. WANG, ZEPLIN II, UCLA 11

Details of ZEPLIN II

1. Fiducially volume: 40kg.2. Two wire-frames provide both:

• electron extraction field• Electro-luminescence

field3. 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, 2001 H. WANG, ZEPLIN II, UCLA 12

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, 2001 H. WANG, ZEPLIN II, UCLA 13

ZEPLIN II system Setup

Lead Shielding

The central detector

Active Veto

Liquid xenon target

Copper cast vacuum and target vessel

July 7, 2001 H. WANG, ZEPLIN II, UCLA 14

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, andXenon port

July 7, 2001 H. WANG, ZEPLIN II, UCLA 15

ANSYS finite element analysis for field configurations

July 7, 2001 H. WANG, ZEPLIN II, UCLA 16

CsI test results

H-2sV-20mV

(E. Aprile et al., NIM A343 1994, 129-134)

July 7, 2001 H. WANG, ZEPLIN II, UCLA 17

Expected limit for ZEPLIN II

and ZEPLIN IV

July 7, 2001 H. WANG, ZEPLIN II, UCLA 18

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 1000.

•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