Direct Detection of SUSY Cold Dark Matter in Liquid Xenon

“ The XENON Project” Direct Detection of SUSY Cold Dark Matter in Liquid Xenon

One Tonne - Have we got what it takes?

Columbia University: E. Aprile (PI), E. Baltz, A. Curioni, K-L. Giboni, C. Hailey, L. Hui, M. Kobayashi, P. Majewski and K.Ni Brown University: Richard Gaitskell Princeton University: Tom Shutt Rice University: Uwe Oberlack LLNL: William Craig

NESS02 – September 19, 2002 Elena Aprile The XENON Project: Overview

• Liquid Xenon is an excellent target material for Cold Dark Matter WIMPs, and likely the only practical one, for a sensitive experiment of the scale required by most SUSY predictions. Driven by the compelling science case and with the confidence in the LXeTPC technology which Columbia has developed for g-ray astrophysics (with NASA support), we submitted a proposal to NSF on Oct 11, 2001, for an accelerated two year research program leading to a demonstration of the XENON design concept with a 10 kg prototype.

• The 1- tonne XENON experiment would be realized with an array of ten position sensitive LXeTPCs, each with 100 kg Xe target and sourrounded by several cm of LXe as active scintillator shield. Using both light and charge (amplified in gas phase) and the intrinsic imaging capability of a TPC, the goals for XENON are a low energy threshold (~16 keV) and an excellent electron/nuclear recoil discrimination (>99.5%). With an estimated total background rate of 2 x 10-5 counts/kg/keV/day XENON should reach the sensitivity of 1 event /100 kg/year or s~10-10 pb, probing the lowest SUSY parameter space.

• Following a SAGENAP review on March 12, 2002, NSF has funded the 2-year program, starting on September 1, 2002. The outcome of this R&D phase will define the design for the 100 kg unit module, taking into account the low activity materials requirement. For the next phase of construction and underground operation of the XENON array, both the development /support of US National Underground Laboratory, and a strong worldwide collaboration, will be vital for the success of the XENON dark matter experiment.

NESS02 – September 19, 2002 Elena Aprile Current & Next Generation Experiments & SUSY Theory Range

http://dmtools.berkeley.edu

Edelweiss (June 2002) ~0.25 event/kg/d

~1 event/kg/yr

~ 1 event/100 kg/yr

NESS02 – September 19, 2002 Elena Aprile Typical WIMP Signal

Xe Eth=16 keVr gives 1 event/kg/day • dN Ú dE Er Example cross-section shown is at current (90%) exclusion limits of existing experiments †

Experimental Requirements ‡ Energy Threshold : as low as possible ‡Target Mass: as high as possible ‡ Background: as low as possible NESS02 – September 19, 2002 Elena Aprile Liquid Xenon for WIMPs Direct Detection

q High mass Xe nucleus (A ~131) good for WIMPs S.I. Interaction ( s ~A2 )

q Odd Isotopes with large spin-dependent enhancement factors

q High atomic number (Z=54) and density (r=3g/cc) of liquid state good for compact and flexible detector geometry

q Production and purification of Xe with << 1ppb O2 in large quantities for tonne scale experiment. “Easy” cryogenics at –100 oC

q Excellent ionizer and scintillator with distinct charge/light ratio for electron/nuclear energy deposits for high background discrimination

NESS02 – September 19, 2002 85 Elena Aprile q No long-lived radioactive isotopes. Kr contamination reducible to ppb level … and for Solar n and 0nbb Decay

124Xe 126Xe 128Xe 129Xe 130Xe 131Xe 132Xe 134Xe 136Xe (0.10%) (0.09%) (1.92%) (26.4%) (4.07%) (21.2%) (26.9%) (10.4%) (8.87%) Mostly Odd Mostly Even

Separation here bb-nucleus

136 Odd enriched Even enriched:containing Xe • Solar neutrino • 2nbb/0nbb

• Dark matter Spin dependent • Dark matter Spin independent

XMASS EXO

LXe prototype in Kamioka LXe prototype at Stanford

NESS02 – September 19, 2002 Elena Aprile Xenon Phase Diagram

NESS02 – September 19, 2002 Elena Aprile Properties of LXe vs Ge and Si

NESS02 – September 19, 2002 Elena Aprile Ionization and Scintillation in Liquid Xenon

I/S (electron) >> I/S (non relativistic particle) Ionization (Xe+, e) Excitation (Xe*)

Alpha scintillation )

Electron charge

electron scintillation

Recombination L/L0 or Q/Q0 (% Alpha charge 1 3 Xe2* ( Su , Su ) ﬁ 2Xe+hn (175 nm) Electric Field (kV/cm) Fast Slow

NESS02 – September 19, 2002 Elena Aprile Recombination and Attachment reduce electron signal

t=1/ks[S] l= t vd = tmE

e- + S Æ S - ks • ‡ High drift field • ‡ High purity gas • ‡ low-outgassing materials

choice of purifiers and materials must be compatible with the low cosmogenics requirements

NESS02 – September 19, 2002 Elena Aprile Spatial Resolution

Technical limits field line distortions, electronic noise, and effects specific to signal readout scheme Physical Limit Electron Diffusion electron cloud Ld r td = vd = mE m = mobility vd

r spread in electron cloud: s = 2Dtd E vd transverse D = diffusion coefficient longitudinal diffusion depends on drift path Ld eD 2 eD = k T = < e > T =165K Æ ª 0.3eV m 3 LXe m r r electron energy depends on E Æ D(E) s a few mm ª Ld m

NESS02 – September 19, 2002 Elena Aprile Energy Resolution

• Statistical limit 1/ N N = E /W - value DE F FW • “Fano Factor” limit = 2.35 = 2.35 E N E WF (liquid argon) is 2.54 DE ª 4keV @ 1MeV WF (liquid xenon) is 0.64 DE ª 2keV @ 1MeV

• If all charges are collected and if full energy is absorbed in the liquid, the contributions to the energy resolution of a liquid ionization chamber are: 2 2 2 2 1/ 2 DET = 2.35[DEi + DEn + DEs + DEr ]

DEi •Ionization straggling

DEn •Electronic noise

DEs •Positive ion effect

DEr •Rise time effect

NESS02 – September 19, 2002 Elena Aprile Columbia Experience with LXe Detectors

q A 30 kg Liquid Xenon Time Projection Chamber developed and successfully tested at balloon altitude for Compton Imaging and Spectroscopy of MeV Cosmic Gamma- Ray Sources

q NASA supported R&D on LXe detector technology and development of balloon-borne LXeGRIT payload.

q Road to LXeGRIT: extensive studies of LXe ionization and scintillation properties, purification techniques to achieve long electron drift for large volume application, energy resolution and 3D

NESS02 – September 19, 2002 imaging, electron mobility etc. Elena Aprile The Columbia LXeTPC

30 kg

• 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

NESS02 – September 19, 2002 Elena Aprile Electron vs Nuclear Recoil Discrimination in XENON

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

Nuclear recoils from •WIMPs •Neutrons Gas Electron recoils from •Gammas s •Electrons μ

~ anode Proportional scintillation depends on type of recoil and grid applied electric field. e-

Drift Time electron recoil → S2/ S1 >> 1 Liquid E

nuclear recoil → S2/ S1 ~0 40ns but detectable if E large ~ g-ray cathode

NESS02 – September 19, 2002 Elena Aprile 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. Active shield very effective for 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 ).

NESS02 – September 19, 2002 Elena Aprile XENON TPC Signals Time Structure

Both Direct and Proportional Scintillation Signals detected by the same PMTs Array

t~45 ns

150 µs (300 mm) • 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)

NESS02 – September 19, 2002 Elena Aprile Detection of Xe Light with a CsI Photocathode

• Stable performance of reflective CsI photocathodes with high QE of 31% in LXe has been demonstrated by the Columbia measurements

• CsI photocathodes can be made in any size/shape with uniform response, and are inexpensive.

• LXe negative electron affinity Vo(LXe)= - 0.67 eV and the applied electric field explain the favorable electron extraction at the CsI-liquid interface. Aprile et al. NIMA 338(1994) Aprile et al. NIMA 343(1994)

NESS02 – September 19, 2002 Elena Aprile XENON Baseline Readout: PMTs • Hamamatsu Low Temperature Tube (R6041)

u Developed for LXe detectors. Shown to work reliably at low T and at P< 5 atm

u Metal construction, compact design, recent tests at Columbia with custom designed HV divider show simultaneous light/charge with good yield

u Low Background version under study by Hamamatsu

u Low Quantum Efficiency~10-15%

• Hamamatsu Low Background Tube (R7281)

u Being tested by Xmass Collaboration • Room temperature tests only so far

u Metal construction, and giving lower backgrounds • ~500 cts/tube/day (XENON baseline goal:~ 100)

u Higher Quantum Efficiency~27-30% • Uses longer optics which give better focusing (could be accommdated in XENON)

NESS02 – September 19, 2002 Elena Aprile Light Collection Efficiency for XENON

Hamamatsu R6041

Assumptions

ÿ Wph : 13 eV

ÿ lph: 1.7 m ÿ Quenching Factor: 25% ÿ Q.E. of PMTs: 26% ÿ Q.E. of CsI : 31% ÿ R.E of Teflon Wall: 90% ÿ Xe Mass: 100 kg ÿ 37 PMTs (2 inch) array

NESS02 – September 19, 2002 Elena Aprile Baseline - Simulation Results

16 keV recoil threshold event • Assumes 25% QE for 37 phototubes, and 31% for CsI photocathode

• With a Wph= 13 eV, a 16 keV (true) nuclear recoil gives ~ 24 photoelectrons. The CsI readout contributes the largest fraction of them. • Multiplication in the gas phase gives a strong secondary scintillation pulse for triggering on 2-3 PMTs. We trigger on this amplified (100 – 1000 UV photons/electron) CsI signal. • Coincidence of direct PMTs sum signal and amplified light signal from CsI. • Trigger being the last signal in time sequence‡ post-triggered digitizer read out. Trigger threshold can be set very low because of low event rate and small number of signals to digitize. PMTs at low temperature‡ low noise • Even w/o CsI (replaced by reflector) we still expect ~6 pe. Several ways to improve light collection possible

NESS02 – September 19, 2002 Elena Aprile Scintillation Efficiency for Nuclear Recoils in LXe

F. Arneodo et al. NIMA 449(2000)

Si Lindhard theory

LXe no LXe data at low energy

NESS02 – September 19, 2002 Elena Aprile Neutrons Induced Background

Soft neutrons from muons Muon flux vs overburden

Proposed NUSL Homestake ‡not important if deep underground. 106 Current Laboratories (a,n) neutrons from rock WIPP 5 ‡Readily reduced by ≈ 20 cm 10 Soudan -1

moderator. y Kamioka -2 104 Very high energy neutrons Gran Sasso

from muons Muon Intensity, m 3 10 Homestake Baksan (Chlorine) ‡ Needs further study. Depends on Mont Blanc site. 102 Sudbury From U/Th from materials NUSL - Homestake inside shield 101 5 6 7 8 9 2 3 4 5 6 7 8 9 ‡ Low cosmogenic materials 103 104 selection Depth, meters water equivalent

NESS02 – September 19, 2002 Elena Aprile Radioactive impurities in Xe.

• No long lived Xe isotopes.

• 85Kr ‡ - • t1/2=10.7y, b 678 KeV. g and b induced background • Commercial research grade Xe: • 10 ppm Kr -> ≈ 200 counts/kg/keV/day • Need 0.1 ppb for 1x10-5 counts/kg/keV/day (after discrimination). • 42Ar ‡ More readily removed than Kr. • Rn ‡ Emanation from components, welds. -4 • Typical values: ≤ 0.1 mBq -> ≈ 10 counts/kg/keV/day • Probably adsorbed on cryostat surfaces. • U, Th, K ‡ • Very low solubility for ionic impurities in Xe. • Particulates removed by filtering.

NESS02 – September 19, 2002 Elena Aprile Background from PMTs

Standard PMTs very hot. • Example: Borexino 8” Ø “ultra-low-background” PMTs: U 1.4 Bq; Th 0.2 Bq; K 1.9 Bq • Problems: Glass, Ceramic, Dynodes, Components New PMTs. Quartz windows, metal cans. • Hamamatsu R7281Q (being tested for XMASS) • activity: 4.5 (tube) + 1.6 (base) mBq • Nearly a 1000 fold-improvement! • Burle – microchannel-plate based PMT. • R&D for low background, low temperature PMT for XENON started • Goal: Cu+sapphire ≈1g glass MCP.

Monte Carlo simulations‡With 20 PMTs, each at 6 mBq, 5 cm fiducial volume cut ‡background after discrimination = 2 x 10-5 counts/kg/keV/day.

NESS02 – September 19, 2002 Elena Aprile GEMs Charge readout : a promising alternative to PMTs

High gain in pure Xe with 3GEMs demonstrated Coating of GEMs with CsI 2D readout for mm resolution R&D for XENON- CERN/Rice/Princeton

Bondar et al.,Vienna01

NESS02 – September 19, 2002 Elena Aprile 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 with g and neutron sources (Collaboration)

NESS02 – September 19, 2002 Elena Aprile Construction Costs

• What do you estimate to be the construction costs for the 100 kg exp?

u Include shielding, readout and support equipment costs (Xe, Purification, Cryo)

u [ $0.32M ] Xe: 100 kg Active Target + ~100 kg Active Shield • $1.6/g ($6/g CDMS cryo-detector grade) • 1 module $320k of Xe • (1 tonne active Xe -> $1.6m)

u [ ~$1M ] Xe Purification + Gas System / Handling / Circulation

u [ ~$0.5M] Kr Removal

u [ ~$1M ] Design + Construction of 1x100 kg module

u [ ~$0.2M ] Clean Room Class 1000

u [ ~$1.6 M ] Readout, DAQ, Shield • [$4.6M] Total

NESS02 – September 19, 2002 Elena Aprile XMXMASSASS experimentexperiment atat KamiokaKamioka

-- DoubleDouble PhasePhase XeXe detectordetector forfor darkdark mmatteratter search-search- forfor XMAXMASSSS ccollaollaboraborationtion M. Yamashita (Waseda university)

Contents ・Introduction to XMASS ・ Double phase detector and shield setup ・ Preliminary result and Background ・ Summary 23/Feb/2002 NDM02 at IISAS (Kyoto)

NESS02 – September 19, 2002 Elena Aprile The Japanese Dark Matter Program at Kamioka

NESS02 – September 19, 2002 Elena Aprile NESS02 – September 19, 2002 Elena Aprile XMASS Collaboration

●Tokyo University ICRR,Kamioka observatory Y. Suzuki, M. Nakahata, Y. Itow, M. Shiozawa, Y. Takeuchi, S. Moriyama, T. Namba, M. Miura, Y. Koshio, Y. Fukuda, S. Fukuda ICRR, RCNN T. Kajita, K. Kaneyuki, A. Okada, M. Ishituka ● Saga University T. Tsukamoto, H. Ohsumi, Y. Iimori ● Niigata University K. Miyano, K. Ito ● Tokai University K. Nishijima, T. Hashimoto ●XMASS ● Gifu University S. Tasaka ◎ Xenon MASSive detector for Solar neutrino ● Waseda University (pp/7Be) S. Suzuki, M. Yamashita, T. Doke, J. Kikuchi, K. Kawasaki ◎ Xenon detector for Weakly Interacting ● TIT MASSive Particles Y. Watanabe, K. Ishino ● Seoul National University (Dark Matter search) Soo-Bong Kim, In-Seok Kang Xenon neutrino MASS detector ● INR-Kiev ◎ Y. Zdesenko, O. Ponkratenko (double beta decay) ● UCI H. Sobel, M. Smy, M. Vagins

NESS02 – September 19, 2002 Elena Aprile Idea for detector

Now, we develop two type of detector for low background experiment. Self shielding Double phase Surrounded by 30cm Xenon Particle id for rejection BG

10t scale

NESS02 – September 19, 2002 Elena Aprile Set up (shield)

Detector is cooled and kept H.V. and signal by cold finger contact feed through is out side of the shield from Liq. N2 at 170K.

Liq. N2 Detector Dewar OFHC(5cm)

Boric acid 2 OFHC(5cm) (5g/cm )

Lead (15cm) Polyethylene(15cm)

NESS02 – September 19, 2002 Elena Aprile Set up (detector)

Cold finger gas filling line

Wire set Gas Xe (Grid1,Anode Grid2) Liq. Xe(1kg) PTFE Teflon OFHC vessel (Reflector) (5cm) MgF Window 2 PMT with Ni mesh (cathode)

NESS02 – September 19, 2002 Elena Aprile •1kg Double Phase Xe Detector

Teflon surrounded by 5cm OFHC PMT Field shaping ring

NESS02 – September 19, 2002 Elena Aprile uCalibration

57 Co (122keV) σ/E = 15 % counts 2.4 [p.e./keV] at 250[V/cm] with R7281MgF2 (Q.E.30%) (HAMAMATSU(prototype)) p.e. 137Cs 662keV counts

p.e.

NESS02 – September 19, 2002 Elena Aprile Background Spectrum

flow Super Radon free air (3mBq/m3) around detector

Low energy part

clean room in Kamioka mine Kr free Xe(10ppb Kr) #normal Xe(~10ppm）

NESS02 – September 19, 2002 Elena Aprile uRejection

Preliminary Preliminary

gamma region

Rejected

Recoil region Recoil

Need to define Recoil band of this detector by neutron source

Performance was not good in low energy part (‘_’)

NESS02 – September 19, 2002 Elena Aprile uBackground rate in Z-axis normalized in radius PMT

0 Z-axis

9.5cm Z-axis Z-axis

PMT

Background from Outside. need to reduce it !

Z-axis Z-axis

NESS02 – September 19, 2002 Elena Aprile uBackground(Monte Carlo)

Test Run These material was main Total component of background. (using value of 1σupper limit) PMT steel(shaping ring)

PMT Base steel vessel “DECAY4” has been used 85Kr for the simulation: Y. Zdesenko, O. Ponkratenko Kr 10ppb

NESS02 – September 19, 2002 Elena Aprile Background(Improvement)

Material Total Material Total (Bq/PMT) (Bq/PMT)

PMT(prototype) 3.7× 10-1 PMT(R7281Q) 1.7× 10-1 HAMAMATSU HAMAMATSU

PMT base 1.8×10-1 PMT(with R7281Q) 1.6×10-3 HAMAMATSU HAMAMATSU

Steel(Vessel, 3×10-2 OFHC <1.5×10-3 shaping ring …) (Bq/kg) (Bq/kg)

NESS02 – September 19, 2002 Elena Aprile Expected results (Spin Independent case)

Quench factor = 0.2 Test run Kr free natural Xenon preliminary (Kr 10ppb)

no rejection low back PMT (expected)

99% rejection expected

EDELWEISS astro-ph/0106094 CDMS Phys. Rev. Lett. 84 (2000) p.5699 DAMA/NaI-1 to 4 combined, Phys. Lett. B480 (2000) 23-31

NESS02 – September 19, 2002 Elena Aprile XMASS: Next Step (2003)

NESS02 – September 19, 2002 Elena Aprile