XENON Looking for WIMPs in Liquid Xenon

Elena Aprile Department and Columbia Astrophysics Laboratory http://www.astro.columbia.edu/~lxe/XENON/

Dark Matter 2004 Elena Aprile The XENON Collaboration

Columbia University Elena Aprile (PI),Karl-Ludwig Giboni, Pawel Majewski, Kaixuan Ni, Bhartendu Singh and Masaki Yamashita Brown University Richard Gaitskell, Peter Sorensen, Luiz DeViveiros University of Florida Laura Baudis, David Day Lawrence Livermore National Laboratory William Craig, Adam Bernstein, Chris Hagmann Tom Shutt, John Kwong, Kirk McDonald Rice University Uwe Oberlack ,Omar Vargas Daniel McKinsey, Richard Hasty, Hugh Lippincott

Dark Matter 2004 Elena Aprile Dark Matter 2004 Elena Aprile Promise of Liquid Xenon for WIMPs

! High atomic number (Z=54) and density (ρ=3g/cc) permit a compact self- shielding detector geometry.

! Simultaneous measurement of ionization and scintillation signals produced by WIMP interactions and the different amplitude/time response of these signals for e/n recoils provide powerful and efficient background discrimination.

! It is available in large quantities at a reasonable cost (~1k$/kg). “Easy” cryogenics at –100 oC.

! It can be purified to achieve long distance drift of free ionization electrons . Additional processing can reduce traces of radioactive 85Kr , 42Ar, Ra to the low level required. No long-lived radioactive Xe isotopes.

! It contains even/odd Isotopes suitable for spin-independent/ spin-dependent interactions.

Dark Matter 2004 Elena Aprile Projected Sensitivity of XENON vs Current Direct Detection DM Limits

~0.25 event/kg/d

~1 event/kg/yr

~ 1 event/100 kg/yr

XENON100 sensitivity ~2x10 -45 cm 2 in 3 months operation at a background level < 1x10-5cts/keVee/kg/day, after rejection

Dark Matter 2004 Elena Aprile Typical WIMP Signal

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

Requirements & XENON Goals " Energy Threshold : as low as possible < 16 keV " Target Mass: as high as possible > 1 ton " e/n Discrimination: as high as possible > 99.5%

-5 Dark Matter 2004 " Background: as low as possible < 1x10 cts/keVee/kg/day Elena Aprile XENON Nuclear Recoil Discrimination

Simultaneous Measurement of direct scintillation and charge (proportional scintillation)

Direct and Proportional scintillation depend Nuclear recoils from on type of recoil and applied electric field. •WIMPs • Gas Electron recoils from •Gammas s

μ μ •Electrons μ μ

1

~ anode

Alpha scintillation e

m

i

T

-

t

Electron charge f e

i

r

D

electron scintillation s E n Liquid

0

Alpha charge 4 ~ γ-ray L/L0 or Q/Q0 (%)

Electric Field (kV/cm) cathode Dark Matter 2004 Elena Aprile The XENON-1T Experiment : Design Overview

• XENON-1T design modular.

• 10 independent 3D position sensitive XeTPC operated in dual phase.

• Fiducial target self-shielded by LXe active scintillator.

• Target cooled by shield LXe at ~ 165 K by refrigerator.

Dark Matter 2004 Elena Aprile XENON TPC Signals Time Structure

τ~45 ns

150 µs (300 mm)

•Three distinct light signals; CsI important for low threshold and trigger •Z from drift time; XY from proportional light signals on PMTs array. •3D event localization gives additional background rejection capability

Dark Matter 2004 Elena Aprile Light Collection Efficiency - Simulation Results

Assumptions (16 keV nuclear Results: recoil) : Total light collection efficiency ~40%. •Wph : 23.7 eV • Absorption Length: 1 m Sensitivity = 5p.e./ keV for • Scattering Length: 30 cm nuclear recoil • Quenching Factor: 25% • Q.E. of PMTs: 20% • Q.E. of CsI : 30% • PTFE Reflectivity : 95% • Wires Transparency : 90% • 85 PMTs (2 inch) array

Dark Matter 2004 Elena Aprile X-Y Position Resolution - Simulation Results

Assumptions:

•Ed : 5kV/cm • Prop. Gap: 4 mm (2 atm) • Prop. Field: 13 kV/cm • PMTs: 1cm above Gap

Results: 1.2 cm position resolution for uniformly distributed nuclear recoils with 16 keV

Dark Matter 2004 Elena Aprile Background Considerations for XENON

• Goal: <10-5 counts/kg/keV/day after rejection (99.5%) • Shield: standard, except for use of 5 cm active LXe veto. • Gamma rays from cavern attenuated by Pb (~20 cm) and LXe veto

• No long lived Xe isotopes, except 136Xe 85 β− γ β Readout • Kr " t1/2=10.7y, 678 KeV. and moderator induced background • Commercial research grade Xe: Xe Target • 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. Pb (if needed) SS Xe veto Key issue: radioactivity of readout

Dark Matter 2004 Elena Aprile XENON Baseline PMTs Readout • Hamamatsu Low Temperature Tube (R9288) # Developed for LXe detectors. Shown to work reliably at low T and at P= 5 atm # 2” Metal channel (12 stages, Amplification 106), compact design (4 cm long) # Low Background version under study by Hamamatsu # Quantum Efficiency > 20% # Pulse Rise Time = 2.3 ns, transit time spread = 750ps

• Hamamatsu Low Background Tube (R8778) # Developed for XMASS Collaboration # Box and Line Dynodes, 2”, 112 cm long, 5x106 amplification # Low background • Current value ≈ 70 mBq / PMT ( K / U / Th = 60 / 7 / 4) • Goal ≈ 10 mBq/PMT (K / U / Th = 4 / 2 / 4) # Quantum Efficiency >26% # Pulse Rise Time = 5 ns, transit time spread = 4ns

Dark Matter 2004 Elena Aprile Background from PMTs- Monte Carlo Simulations

With 85 PMTs, each at 10 mBq, total gamma rate < 10 –3 with fiducial volume cut of 5 cm from top and 2 cm from the sides " ~1.5 x 10-5 counts/kg/keVee/day after electron/nuclear recoil discrimination of 99.5%.

Dark Matter 2004 Elena Aprile Current Status of XENON

NSF Proposal : Sept. 2001 R&D Funding : Sept. 2002 R&D Goals: 1. PMTs immersed in LXe 2. ~1 meter electron attenuation length in LXe 3. Operation with few kV/cm electric field 4. Electron extraction from liquid to gas 5. CsI photocathodes immersed in LXe 6. Efficient/Reliable Cryogenic System 7. Alternatives to PMTs 8. Kr removal 9. MonteCarlo simulations 10. Materials screening 11. Electron/nuclear recoil discrimination & quenching factor for <50 keV recoils Next Phase (2004-6): low activity detector (~10 kg) operating in Soudan

Dark Matter 2004 Elena Aprile Single Phase Chamber with 2 PMTs for Charge/Light Studies

4.5kg

57Co

Xe σ/E = 9.3 % Circulation

3 p.e./keV

Dark Matter 2004 Elena Aprile Gas Circulation for High Purity LXe @ High Field

3kV/cm 4kV/cm 3.5kV/cm 2kV/cm

light L/L0 (%) 1kV/cm (%) Q/Q0 ±１％ Field (kV/cm) Time (hour) start circulation

Single Pass Purification through Getter " ~ 1 month for long drift Continuous Recirculation through Getter " ~2 days for long drift

Dark Matter 2004 Elena Aprile Dual Phase Chamber with one PMT for Luminescence Studies

Q PMT Anode Vg Grid E Bi-207 LXe Vc Cathode

Dark Matter 2004 Elena Aprile Studies of alternative readout schemes - Summary • Charge readout # GEMs (Rice) # MWPC (Princeton) • Light detectors # Burle MCP and LAAPD (Columbia &Brown) # Hamamatsu low-background PMTs (Columbia & Florida) # CsI (Columbia &Princeton)

Dark Matter 2004 Elena Aprile Dual Phase TPC Prototype with 7 PMTs Array

Pulse Tube Refrigerator

7PMTs

CsI PC in LXe.

10 cm drift gap with 5kV/cm. Sept. '03 Dark Matter 2004 Elena Aprile Chamber and Cryostat System

Dark Matter 2004 Elena Aprile 10 kg Dual Phase TPC Signals Readout

Dark Matter 2004 Elena Aprile Dark Matter 2004 Elena Aprile First results from ongoing experiment

1 kV/cm Feb 2,2004- present PTR for liquefaction and recirculation at ~5lpm Temperature stability to 0.05 C λ ~ 1 m Measured Cooling power: 140W LXe TemperatureLXe (C)

Days Start Circulation

Long Charge Attenuation Length Demonstrated

Dark Matter 2004 Elena Aprile 122 keV Direct and Proportional Light @ 1 kV/cm …

Direct Light Co-57 Proportional Light Co-57

DATA

0.4 0.20 x 0.6+-0.1 122 keV E ⋅Q = γ f × × N pe Pce Qe = 8.2 +-1.4 ESTIMATE-MC Wph

23.6 eV Light Collection (MC)=0.033 Dark Matter 2004 Elena Aprile Consistent with expectation

MC Co-57 122 keV @ 5kV/cm

No CsI With CsI

Next Step: Introduce CsI Photocathode Dark Matter 2004 Elena Aprile Current Status of XENON-Summary

NSF Proposal : Sept. 2001 R&D Funding : Sept. 2002 R&D Goals: 1. PMTs immersed in LXe 2. ~1 meter electron attenuation length in LXe 3. Operation with few kV/cm electric field 4. Electron extraction from liquid to gas 5. Efficient/Reliable Cryogenic System 6. CsI photocathodes immersed in LXe 7. Alternatives to PMTs 8. Kr removal 9. MonteCarlo simulations 10. Materials screening 11. Electron/nuclear recoil discrimination & quenching factor for <50 keV recoils Next Phase (2004-6): low activity detector (~10 kg) operating in Soudan WHAT NEXT? " XENON-100 WHERE? " NUSEL? LNGS? SNOLAB? Dark Matter 2004 Elena Aprile