1

Expected rates for various targets

For a heavy target nucleus such as Xe, a very low recoil energy threshold is crucial.

The expected rate, integrated above threshold of ~16 keV is 1 events/ kg/day

2

WIMP Direct Searches with Recoil Discrimination

Project Detectors Active Mass Rejection Method Location( mwe) Timescale

CDMS II CryoArray

Si and Ge 2 kg (Si) +5 kg (Ge) 1 tonne

Phonon and Charge Soudan (2200) 2002 – 2007 Start 2006 ?

EDELWEISS I EDELWEISS II

Ge 3 X 320 g ~ 1 kg 21 X 320 g ~ 7 kg

Phonon and Charge Frejus (4600) 2002 - 2004 Start 2004 ?

CRESST II CaWO4 33 X 300 g ~10 kg Phonon and Scintillation

Gran Sasso (3800) 300 g setup 2002

ZEPLIN II ZEPLIN IV

LXe 30 kg 1 tonne

Charge and scintillation Boulby (3300) Construction 2001 Start 2007 ?

ZEPLIN III ZEPLIN-MAX

LXe 6 kg 1 tonne

Charge and scintillation Boulby (3300) Construction 2001 Start 2006 ?

XMASS LXe 1 kg 20kg

Charge and scintillation Kamioka (2600) Installed 2001 Construction 2002

XENON

LXe 10 kg 100 kg 1 tonne

Charge and scintillation Homestake (>4000) Operational 2004 Start 2005 ? Start 2007 ?

DRIFT 1 , 2 DRIFT 3

CS2 < 1 kg 100kg

Recoil direction Boulby (3300) Installed 2001 Start 2004 ?

3

Electron vs Nuclear Recoil Discrimination(Direct & Proportional Scintillation )

Dri

ft T

ime

E

anode

e-

grid

cathode

~1μ

s~4

0 ns

Nuclear recoil from•WIMP •NeutronElectron recoil from•gamma•Electron•Alpha

Gas

Liquid

Measure both direct scintillation(S1) and charge(proportional scintillation) (S2)

Proportional scintillation depends on type of recoil and applied electric field.

electron recoil → S2 >> S1nuclear recoil → S2 < S1 but detectable if E large

Dual Phase Detection Principle Common to All LXe DM Projects

4

The XENON TPC Signals

• Three distinct signals associated with typical event. Amplification of primary scintillation light with CsI photocathode important for low threshold and for triggering.

• Event depth of interaction (Z) from timing and XY-location from center of gravity of secondary light signals on PMTs array.

• Effective background rejection direct consequence of 3D event localization (TPC)

5

The XENON Experiment : Design Overview

• The XENON design is modular.An array of 10 independent 3D position sensitive LXeTPC modules, each with a 100 kg active Xe mass, is used to make the 1-tonne scale experiment.

• The fiducial LXe volume of each module is self-shielded by additional LXe. The thickness of the active shield will be optimized for effective charged and neutral background rejection.

• One common vessel of ~ 60 cm diameter and 60 cm height is used to house the TPC teflon and copper rings structure filled with the 100 kg Xe target and the shield LXe (~50 kg ).

6

A Liquid Xenon Time Projection Chamber for Gamma-Ray Astrophysics

7

The Columbia 10 liter LXeTPC

• 30 kg active Xe mass• 20 x 20 cm2 active area• 8 cm drift with 4 kV/cm• Charge and Light readout• 128 wires/anodes digitizers• 4UV PMTs

8

UCLA ZEPLIN II

9

ZEPLIN II

10

ZEPLIN II ZEPLIN IV

The latest design as at DM2002

The latest design as at DM2002

30 kg 1000 kg

11

UKDM ZEPLIN III

12

ZEPLIN III

14

The LXe Program at Kamioka

Liq. Xe(1kg)9.5 cm Drift

Wire set(Grid1,AnodeGrid2)

PTFE Teflon(Reflector)

MgF2 Windowwith Ni mesh(cathode)

OFHC vessel(5cm)

gas filling line

Cold finger

PMT

Gas Xe

with 99% rejection

with new PMTs no rejec.

present

XMASS

15

… and for Solar and 0Decay

124Xe (0.10%)

126Xe (0.09%)

128Xe (1.92%)

129Xe (26.4%)

130Xe (4.07%)

131Xe (21.2%)

132Xe (26.9%)

134Xe (10.4%)

136Xe (8.87%)

Mostly Odd Mostly Even

-nucleusSeparation here

Odd enriched• Solar neutrino• Dark matter Spin dependent

: Even enriched containing136Xe•2/0• Dark matter Spin independent

XXMMAASSSS

LXe prototype in Kamioka

EEXXOO

LXe prototype at Stanford

17

The XENON TPC: Principle of Operation

• 30 cm drift gap to maximize active target long electron lifetime in LXe demonstrated

• 5 kV/cm drift field to detect small charge from nuclear recoils internal HV multiplier (Cockroft Walton type)

• Electrons extraction into gas phase to detect charge via proportional scintillation (~1000 UV /e/cm) demonstrated

• Internal CsI photocathode with QE~31% (Aprile et al. NIMA 338,1994) to enhance direct light signal and thus lower threshold demonstrated

• PMTs readout inside the TPC for direct and secondary light need PMTs with low activity from U/Th/K

22

We have experience measuring neutron-nuclear recoil efficiency

typical setup for measurement ofnuclear recoil scintillation efficiencyat University of Sheffield

measured low energy nuclear recoil efficiency of liquid scintillator

Hong, Hailey et. al., J. AstroParticle Physics 20012.9 MeV neutron beam

23

Why Do Nuclear Recoil Scintillation Efficiency Measurements?

• Confirm that measured efficiency at higher energies extends down to lowest energies of interest to a WIMP search

• Confirm result in our particular experimental configuration. Results can vary with Xe purity, light collection efficiency etc.

• Measure true nuclear recoil scintillation pulse shapes

24

Charge readout with GEMs: a promising alternative

• High gain in pure Xe with 3GEMs demonstrated

• Coating of GEMs with CsI

• 2D readout for mm resolution

See Bondar et al.,Vienna01

25

XENON Technical Heritage: LXeGRIT

A 30 kg Liquid Xenon Time Projection Chamber developed with NASA support. 3D imaging detector with good spectroscopy is the basis of the balloon-borne LXeGRIT, a novel Compton Telescope for MeV Gamma- Ray Astrophysics. The LXeTPC operation and response to gamma-rays successfully tested in the lab and in the harsh conditions of a near space environment. Road to LXeGRIT: extensive R&D to study LXe ionization and scintillation properties, purification techniques to achieve long electron drift for large volume application, energy resolution and 3D imaging resolution studies, electron mobility etc.

26

High Purity Xenon for Long Electron Drift and Energy Resolution

And the power of Compton Imaging

27

Compton Imaging of MeV -ray Sources

28

3D capability for event discrimination: Flight Data

29

From the Lab to the Sky: The Balloon-Borne Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT)

Compton Imaging EventsAtm/Cosmic Diffuse MC simulation and Data

30

Background Considerations for XENON

and induced background85Kr (1/2=10.7y): 85Kr/Kr 2 x 10-11 in air giving ~1Bq/m3

Standard Xe gas contains ~ 10ppm of Kr10 Hz from 85Kr decays in 1 liter of LXe.Allowing <1 85Kr decay/day i n XENON energy band <1 ppb level of Kr in Xe

136Xe 2 decay (1/2=8 x 1021y): with Q= 2.48 MeV expected rate inXENON is 1 x 10-6 cts/kg/d/keV before any rejection

• Neutron induced backgroundMuon induced neutrons: spallation of 136Xe and 134Xe take 10 mb and

Homestake 4.4 kmwe estimate 6 x 10-5 cts/kg/d before any rejection reduce by muon veto with 99% efficiency

(,n) neutrons from rock: 1000/n/m2/d from (,n) reactions from U/Th of rock appropriate shield reduces this background to 1 x 10-6 cts/kg/d/keV

Neutrons from U/Th of detector materials: within shield, neutrons from U/Th ofdetector components and vessel give 5 x 10-5 cts/kg/d/keV lower it by x10 with materials selection

31

Background Considerations for XENON

-rays from U/Th/K contamination in PMTs and detector components dominate the background rate. For the PMTs contribution we have assumed a low activity version of the Hamamatsu R6041 ( 100 cts/d ) consistent with recent measurements in Japan with a Hamamatsu R7281Q developed for the XMASS group (Moriyama et al., Xenon01 Workshop).

Numbers are based on Homestake location and reflect 99.5% background rejection but no reduction due to 3D imaging and active LXe shield.

32

How is XENON different from other Liquid Xe Projects?

33

direct proportionaldirect

proportional

direct

drift timedrift time

42000photon/MeVDecay time 45nsec

Signals from 1kg XMASS Prototype

34

XMASS Recoil /γ ray Separation

>99% γ ray rejection>99% γ ray rejection

22 keV gamma ray

Recoil Xenon (neutron source)

Direct scintillation(S1)

Pro

por

tion

al s

cin

till

atio

n(S

2)

(Ref. JPS vol.53,No 3,1998, S.Suzuki)

35

XMASS: low activity PMT development

p.e.

coun

ts

p.e.

coun

ts

57 Co (122keV)

137Cs 662keV

σ/E = 15 %2.4 [p.e./keV] at 250[V/cm]

with R7281MgF2 (Q.E.30%) (HAMAMATSU(prototype)A low activity version of this tube shows ~4.5× 10-3 Bq!

Towards a 20 kg Detector

36

Answer to Question

• LXe long recognized as promising WIMP target for a large scale experiment with relatively simple technology. So far however development effort has been subcritical.

• Low energy threshold and background rejection capability yet to be fully demonstrated.

• Recent move to an underground lab - 1 kg XMASS detector in Kamioka- an important milestone. Scale up to a 20 kg detector of same design (7 PMTs vs 1) started.

• UCLA ZEPLIN II is similar in size and design to XMASS: drift in LXe over ~ 10 cm with low electric. Secondary light pulse from low energy nuclear recoils hard to detect. Scale up to 1 tonne with a monolithic detector (ZEPLIN IV) too risky and unpractical.

• UKDM ZEPLIN III better discrimination power and lower threshold due to high electric field. Design does not present an easy scale up from 6 kg to sizable modules of order 100 kg.

• XENON combines the best of the techniques with a design which can be easily scaled. Strength of experience with a 30 kg LXeTPC for gamma ray astrophysics + critical mass at Columbia with collaborators key experiences in DM searches.

37

XENON Phase 1 Study: 10 kg Chamber

• Demonstrate electron drift over 30 cm (Columbia)

• Measure nuclear recoil efficiency in LXe (Columbia)

• Demonstrate HV multiplier design (Columbia)

• Measure gain in Xe with multi GEMs (Rice and Princeton)

• Test alternative to PMTs, i.e. LAAPDs (Brown)

• Selection and test of detector materials (LLNL)

• Monte Carlo simulations for detector design and background studies (Columbia /Princeton/Brown)

• Study Kr removal techniques (Princeton)

• Characterize 10 kg detector response and with and neutron sources (Entire Collaboration)

38

What next? XENON and NUSL

• The result of the 2yr Phase 1 will be a working 10 kg prototype with demonstrated low ER threshold and recoil discrimination capability. Its move to a deep underground location will initiate science return.

• Phase 2 is for construction and operation of a 100 kg module as 1st step towards 1 tonne. We plan to seek DOE and NSF support and more collaborators

• By this time the situation of a NUSL will be clear. If NUSL is delayed, several alternative locations possible ( Boulby, GS, WIPP, etc.)…but deeper the better..

101

102

103

104

105

106

Muon Intensity, m

-2 y

-1

5 6 7 8 9

1032 3 4 5 6 7 8 9

104

Depth, meters water equivalent

Soudan

Kamioka

Gran Sasso

Homestake (Chlorine)

BaksanMont Blanc

Sudbury

WIPP

Muon flux vs overburden

NUSL - Homestake

Proposed NUSL Homestake Current Laboratories

39

Summary

• Liquid Xenon is an excellent detector material well suited for the large target mass required for a sensitive Dark Matter experiment.

• The XENON experiment is proposed as an array of ten independent, self shielded, 3D position sensitive LXeTPCs each with 100 kg active mass.

• The detector design, largely based on established technology and >10 yrs experience with LXe detectors development at Columbia, maximizes the fiducial volume and the signal information useful to distinguish the rare WIMP events from the large background.

• With a total mass of 1-tonne, a nuclear recoil discrimination > 99.5% and

a threshold of ~ 16 keV, XENON expected sensitivity of 0.0001 events/kg/day in 3 yrs operation, will cover most SUSY predictions.

40

XENON Organization

Subsystem responsibility is allocated amongst the team of experienced co-investigators.

41

XENON Management Approach

• Phase I of the XENON project spans a 2 year period from the funding start date. This instrument development effort has the focused goal of a clear demonstration of the capabilities of a 10 kg LXe detector for a sensitive Dark Matter search.

• The 10 kg prototype defines the roadmap to the Phase II development of a 100 kg detector as one unit of a 1 tonne scale XENON experiment.

• In complexity, the XENON Phase I development does not exceed the NASA funded LXeGRIT experiment and we adopt the successful practices developed during this project.

• We have the required critical mass with extensive expertise in LXe detector technology and other areas relevant to a Dark Matter experiment. This, plus sensible management practices will insure meeting the milestones promised by the end of the 2nd year of Phase I.

42

Management Activities

To coordinate the efforts and insure the appropriate level of communication and exchange of information between the Columbia team and team members at Brown, Princeton, Rice, and LLNL the PI will:

– organize bi-weekly videoconference meetings – obtain monthly progress reports on all sub systems – organize semi annual project reviews with participation of

collaborators and external advisors – prepare yearly progress reports for NSF – encourage student/minority involvement in the research – take full responsibility for the key deliverables to NSF by end of

Phase I

43

Development Schedule

Year 1 activities concentrate on:

• Monte Carlo simulations to guide the design

• Gas system construction and testing

• Neutron recoil efficiency measurements

• Baseline detector development• Alternative detector development• Materials selection and testing

44

Development Schedule (2)

Year 2 activities concentrate on:

• Build of the 10kg prototype• Demonstration of Krypton

reduction• Design of the 100kg instrument

End of Phase I results in near final design of 100kg module and demonstration of all key technologies in the 10 kg prototype.

45

Team Members Expertise

Name Institution Main Expertise Other Experiments

Elena Aprile Columbia Liquid rare gas detectors Ionization and scintillation Time projection chambers

Imaging detectors

LXeGRIT XENA

Chuck Hailey Columbia X-ray Proportional scintillation counters

Scintillators Hard X-ray focusing optics

HEFT ZEPELIN III

Karl Giboni Columbia Imaging detectors Time Projection Chambers

Room temp. semiconductors Analog and Digital Electronics

LXeGRIT XENA

Masanori Kobayasi Columbia Germanium Detectors LXe Time Projection Chamber Imaging detectors data analysis

SELENE LXeGRIT

Uwe Oberlack Rice

(formerly Columbia)

Data acquisition Imaging detectors data analysis

Event reconstruction techniques LXe Time Projection Chamber

COMPTEL LXeGRIT

Tom Shutt Princeton

Low noise electronics Cryogenic detectors

Low radioactivity materials Monte Carlo background studies

CDMS Borexino

William Craig LLNL (formerly Columbia)

Project management System engineering

Instrument development

DRIFT HEFT

Richard Gaitskell

Brown Cryogenic detectors Low noise electronics

Monte Carlo background studies

CDMS CryoArray

46

Budget Details

16%

24%

23%

2%

28%

7%

Senior Personnel

Other Labor

M&S

Travel

Subcontracts

Indirect

Budget breakout (of 2 year total) is consistent with our fast track development of a working prototype

Year 1 request 823k$ Year 2 request 873k$

47

Team Members Presentations

48

Materials Selection and Testing

• Candidate material selection will begin with study of existing databases assembled for other projects.

• LLNL personnel (Craig, Ziock) are associated with ongoing projects requiring low background and will use this existing infrastructure to do testing of candidate materials.

• Close coupling between this effort and the XENON 10/100 kg design team to ensure optimal material choices are incorporated as quickly as possible.

Bill Craig (LLNL)