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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
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
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


Why xe
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…...


Xenon psd and scint ion

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)


Boulby collaboration strategy

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


Towards a 1 ton design
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


Some tasks for 1 ton
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


Zeplin i i iii 2001 2
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


Zeplin 1 ton concept

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


Zeplin xenon predictions

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


One concept

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


Zeplin locations at boulby

ZEPLIN-MAX

ZEPLIN-II

ZEPLIN-III

ZEPLIN locations at Boulby

Stub 2

JIF Facility

ZEPLIN-I


Ukdmc xenon zeplin i

Xe+

+Xe

Xe2+

+e-

(recombination)

Xe*

Xe** + Xe

+Xe

Xe2*

175nm

175nm

Triplet

Singlet

3ns

27ns

2Xe

2Xe

UKDMC Xenon - ZEPLIN I


Zeplin i underground
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



Zeplin i laboratory tests
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


Zeplin i laboratory tests1

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


Zeplin i laboratory tests2
ZEPLIN I Laboratory tests

  • Light Yield

    • Increases at low energy

  • Spatial Uniformity

    • 137Cs Source

Data

Theory


Zeplin i discrimination
ZEPLIN I Discrimination

Gamma

source

(ns)

n

Neutron

source

(ns)

10-20keV

20-30keV



Zeplin i results
ZEPLIN I - Results

Predictions for 1 year

85Kr < 10-17 atoms/atom


Pmt removal for scale up

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


Gem prototype target
GEM Prototype Target NIMA 343 (1994), 121.

High or low field operation

In-house CsI photocathode production

GEMs of Sheffield design from CERN


Gem rig
GEM Rig NIMA 343 (1994), 121.


Zeplin ii
ZEPLIN II NIMA 343 (1994), 121.

(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


Zeplin iii
ZEPLIN III NIMA 343 (1994), 121.

(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


Ukdmc bdmc future

10 NIMA 343 (1994), 121.-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


Dama xenon
DAMA Xenon NIMA 343 (1994), 121.

  • 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)


Xenon kamioka scint ion
XENON - Kamioka (Scint/Ion) NIMA 343 (1994), 121.

  • 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


Towards 1 ton

Possibilities NIMA 343 (1994), 121.

  • 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


Current direct limits

- NIMA 343 (1994), 121.

-

-

-

-

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


Summary
Summary NIMA 343 (1994), 121.

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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