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c Roland Lüscher

Imperial College Of Science, Technology and Medicine, Prince Consort Road, London, SW7 2BZ, UK

Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK

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cB Ahmed, A Bewick, D Davidge, JV Dawson, AS Howard, I Ivaniouchenkov, WG Jones, MK Joshi, V Lebedenko,I Liubarsky, R Lüscher, T J Sumner, J J Quenby

Blackett Laboratory, Imperial College of Science, Technology and Medicine, LondonGJ Alner, SP Hart, JD Lewin, RM Preece, JW Roberts, NJT Smith, PF Smith

Particle Physics Department, Rutherford Appleton Laboratory, Chilton, OxonMJ Carson, T Gamble, VA Kudryavtsev, TB Lawson, MJ Lehner, PK Lightfoot, JE McMillan,B Morgan, SM Pealing, M Robinson, NJC Spooner, DR Tovey

Department of Physics and Astronomy, University of SheffieldDB Cline, H Wang, Y Seo, M Atac, F Sergiampietri

Physics and Astronomy, UCLAP Picchi, F Pietropaolo

CERN/ICGF-CNR-Torino/INFN-PadovaJT White, J Gao

Department of Physics, Texas A&M UniversityU Cotti, M Reyes, L Villasenor

Institute of Phys. and Maths., UMSNH, Morelia, MexicoA Zepeda

Physics Department, CINVESTAV, Mexico CityCJ Hailey, WW Craig, M Sileo, P Graham, J Hong

Astrophysics, Columbia University

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cEvidence for dark matter Rotation curve of a spiral galaxy:

• Measured circular rotation velocities as a function ofradius.

• Contributions due to the observed disk and gas, andfrom the dark halo are also shown.

Cosmology•• All viable cosmological scenariosAll viable cosmological scenarios

involve CDMinvolve CDM•• Consens Consens that ~7% of cluster DM isthat ~7% of cluster DM is

baryonicbaryonic•• Halo sizes are larger - typically 200Halo sizes are larger - typically 200

kpckpc in spirals in spirals

Particle Physics•• “Natural” “Natural” SUSY models have minimumSUSY models have minimum

sspp ~10 ~10-10-10 pbpb•• SUSY predicts a WIMP: the SUSY predicts a WIMP: the neutralinoneutralino

excluded

prob

ably

exc

lude

d by

acc

el.

theoretically plausiblemass region

1 10 100 1000

1000

10

0.1

0.001

WIMP mass (proton masses)

events per kg per day

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cBoulby Boulby minemine (North Yorkshire, UK)

1100m undergroundin salt&potash mine

Low radioactivityrock

Low Rn level

JIF-bid to create newclean undergroundarea and surfacecontrol-room

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cMine Mine specificitiesspecificities::

10-13

10-11

10-9

10-7

10-5

10-3

10-1

0 1000 2000 3000 4000 5000 6000 7000 8000

Muon FluxNeutron Production

Muo

n Fl

ux (c

m-2s-1

) or N

eutro

n Pr

oduc

tion

(g-1

s-1)

Depth (mwe)

Bou

lbySoud

an

Gra

n Sa

sso

Kam

ioka

Frej

us

Mon

t Bla

nc

Sudb

ury

• µ flux attenuated by 10-6:

• Low radon levels ~5 Bqm-3

(comparable to LNGS)

• Background from surroundingrock:

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cUKDMC/BDMC underground facilities ...UKDMC/BDMC underground facilities ...

Existing areas

New area

50 m

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c

DirtyStores

8m

20m

ElectricDarkrm

Clean Room

Experimental Halls - partitioned as required

Mess/Change

Stores

Wshop

Drift AreaTransfer

Clean-off

20m

47m14m

8m

6m

Runningboards

… and surface building… and surface building

… underground building ...… underground building ...

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cWIMP DIRECT DETECTION

Expected featureless differentialnuclear recoil energy spectrum forstationary detector---> looks like e- background

•• Kinematics Kinematics

•• Observed spectrum Observed spectrum

Background rejection tools:

(1) Nuclear recoil discrimination(2) Directional signal

WIMPWIMPMD MT

dRdE R

= RoEor

e -ER/Eor

recoil energy

incident energy

kinematic factor = 4MDMT/(MD + MT)2

event rate per unit mass

total event rate (point like nucleus)

1 2 3 4 5 6 7 8 9 100

(Eor

/Ro)

*dR

(vE,v

esc)/

dER

E/(E0r)

0123456789

10

dRdE = Ro S(E) F2(E) I(A)

obs

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cWIMP-target interaction

Signal Channel DifferencesGe, Si

40keV Nuclear RecoilM¡ 200GeVv = 230km/s

WIMP

Scintillation Ionisation Phonon

+ -+ -

+ -+ -

Pulse Shape Differences

NaI, CsI, Xe Signal Channel Differences

Xe

Gamma ray(or beta decay)

40keV Electron Recoil

Different dE/dX, Range, etc.

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c

• Heavy nuclei (A~130), sensitive to spin-independent interactions(Isi~A2).

• Isotopes with large spin-dependent factors, Isd~0.3 for 129Xe(23Na in NaI or 73Ge in Ge ~0.1) ...… as well as easier enrichement.

• Scintillation in UV (λ=175 nm), low visible energy threshold.• Large quenching factor for Xe recoils g(A)>0.2 (I in NaI: g(A)=0.09,

Na: g(A)~0.3), low recoil energy threshold.• Low background• Scintillation properties enables Pulse-Shape Discrimination

(PSD) between background (electron recoil) and nuclear recoilevents.

• Interesting ionisation properties …• Scale up possibilities (up to 1 ton ?)

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c

Singlet/triplet ratiodiffers betweennuclear and electronrecoils

Recombination onlyrelevant for electronrecoils (=> τ~45ns)

Pulse Shape Analysis

Kubota, NIM 196 (1982), 101;Doke, NIMA 291 (1990) 617

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c

ZonEd Proportionalscintillation in LIquid

Noble gases

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cPreliminaryPreliminary

resultsresultsEnergy spectrumEnergy spectrum

~1 month of data~1 month of data

85Kr level: <10-17 atoms/atom(standard lab purity Xe used) 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 500 1000 1500 2000E (keV)

dE/dx (Emax)

dE/dx (Eav)

Z-I data

Doke parameters:h = 0.16, C = 0.51S2 = .0097/.00032

Scintillation light yield in ZEPLIN I vs.Doke’s empirical formula

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cMean Time DistributionsMean Time Distributions

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100

puls e time cons tant (ns )

ComptonCalibration

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100

puls e time cons tant ns

Am/BeCalibration

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40

obs erved energy keV

neut

ron/

gam

ma

TC r

atio

Fits

t(exp)

t(70%)

t(av90%Ratio

(preliminary)(preliminary)

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cPreliminaryPreliminary

limitslimits

0.00001

0.0001

0.001

0.01

0.1

1 10 100

fitted time cons tant ns

datagamma ca lGD fit

0.00001

0.0001

0.001

0.01

0.1

1 10 100

fitted time cons tant ns

Data: 90 kg*day

Comparisonwith calibration

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cPreliminary limitsPreliminary limits

0.000001

0.00001

0.0001

0.001

1 10 100 1000 10000Mass Gev

WIM

P-N

ucle

on c

ross

sec

tion

pb90 kg days

Projected for 720 kg days

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c• Operating 6.5 kg Kr free (85Kr β emitter) LXe,

using PSD.• 99.5% enriched in 129Xe (spin-dependent

coupl.) -> inelastic scattering• Measured quenching factor ~ 45% - 65%.• Stable operation -105oC.

(Nuovo Cim 19 (1996) 537)

Other Xe detector: DAMA collaboration

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ce-

• Preventsrecombination

• Drifts e-

Nuclear recoil: high primary scintillation, low ionisation yield

Electron recoil: low primary scintillation, high ionisation yield

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cZeplinZeplin-2, a Double-Phase -2, a Double-Phase Xe Xe detectordetector

• Ionisation electron drift towards a high field region in thegas phase.

• Electroluminescence light from the avalanche process

UCLA/Torino/CERNtest chamber:

γ

Electro-luminescence

recoil

Activevolume(1kg LXe)

Gasphase

Primary-Scintillation

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cScintillation, ionisation yield

Free electron lifetime > 5msec

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c

90% nu.rec.<3% elec.rec.

@ 10keV

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c

Construction in progress -finished in a couple of month.

Commissioning and installationin Boulby this year

=> ~30kg detector, Zeplin-2:

UCLA, Torino, Padova, UKDMC

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c

Double-phase,high field

Prototype Chamber (ICSTM)

PM in LXe- Less noise- better light coll.

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c

6kg LXe

Zeplin-3: UKDMC,ITEP, Columbia

31 PMT

Construction started

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cOther Xe detector: Kamioka

• 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 target

Towards 1 ton?

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c

One possibility

… the way towards 1 TON ? … the way towards 1 TON ?ZeplinZeplin - MAX - MAX

Goal:(a) attain 0.0001/kg/d,

(b) diagnostic array with complementarytechniques

UCLA, Columbia, Texas A&M

UKDMC: Sheffield, ICSTM, RALEuropean:

US:ITEP, CERN/Padova, Torino, Coimbra

3 modules

80 kg target

4 sub- units

shielding

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cNew ideas?

• CsI photocathodes in LXe:E.Aprile, NIMA 338 (1994), 328; NIMA 343 (1994), 121. QE = 31%

May also be used as amplifier in Zeplin-2 (UCLA-TAMU)

• APD (avalanche photo-diodes)? (Coimbra)

HVLumines. plate

CsI

PMT

Xe gas

R&D for use in Lxe to be continued

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c

Liquid Xe

Xe Gas

HeCooling

GEMs

CsI

PTFEReflector

CsI

FieldShapingRings

• GEM phototubes in noble gases:http://gdd.web.cern.ch/GDD/A.Buzulutskov, NIMA, 443 (2000), 164.

• MicroMEGAS in noble gas?

(UK R&D):

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cSensitivity of a 1 ton Zeplin:

CDMS IICRESST II

NaI 1996 limit

Zeplin-1 now

Zeplin-1 (+8month)

Zeplin-2/-3

10-3

10-4

10-5

10-6

10-7

10-8

10-9

10-1010 100 1000 [GeV]

Zeplin-1ton

[pb]

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c

DAMA positive signal, PLB 2000;limits, PLB 1996;

CDMS at Stanford, PRL 2000;CRESST 2001;EDELWEISS 2001.