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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

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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 operations at boulby

ZEPLIN Operations at Boulby


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 predicted limits

ZEPLIN I - Predicted Limits


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

High or low field operation

In-house CsI photocathode production

GEMs of Sheffield design from CERN


Gem rig

GEM Rig


Zeplin ii

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


Zeplin iii

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


Ukdmc bdmc future

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


Dama xenon

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)


Xenon kamioka scint ion

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


Towards 1 ton

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


Current direct limits

-

-

-

-

-

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

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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