XENON dark matter experiment

1
XENON dark matter experiment

• T. Shutt
• Princeton University

2
The XENON Collaboration
Columbia University Elena Aprile (PI), Edward
Baltz ,Karl-Ludwig Giboni ,Chuck Hailey ,Lam Hui
Masanori Kobayashi ,Pawel Majewski ,Kaixuan Ni
Rice University Uwe Oberlack ,Omar Vargas
Princeton University John Kwong, Kirk McDonald,
Nathaniel Ross, Tom Shutt Brown University
Richard Gaitskell, Peter Sorensen, Luiz
DeViveiros Lawrence Livermore National
Laboratory William Craig University of Florida
L. Baudis Yale University D. McKinsey, R. Hasty
3
Supersymmetric WIMP rates

• Calculations in minimal supersymmetry framework
  (MSSM).

• Motivation for very large detector clear
• "Generic" test of MSSM possible with 1 ton
• Less restrictive framework can allow lower rates

4
Promise of liquid Xenon.

• Heavy target is good. Xe A131.
• Almost too big Coherence nearly lost!
• Readily purified
• Self-shielding - high density, high Z.
• Can separate spin, no spin isotopes
• 129Xe, 130Xe, 131Xe, 132Xe, 134Xe, 136Xe
• Rich detection media
• Scintillation
• Ionization

Scalable to large masses
5
Basic processes in liquid Xenon

• Complicated atomic processes
• Scintillation - 175 nm
• Singlet ( 3 ns), triplet ( 27 ns)
• Ionization
• Recombination (t 15 ns)
• Energy per quanta (electron recoils)
• charge 20 eV
• Photon 20 eV
• Difference between e and n recoils
• Nuclear recoils, electronic excitations
  suppressed by 5.
• Nuclear recoils suffer recombination

6
Discrimination based on charge

• Electron recoils (background) good charge
  collection (_at_5 kV/cm)
• Nuclear recoils (signal) strong recombination.
• Higher charge density ( 300-500)
• Definitive data so far only for alphas
• (expect alpha nuclear recoil.)

Measurment with alpha particles ( nuclear
recoils)
alpha light
e.r. charge
e.r. light
alpha charge
M. Yamashita, Ph.D Thesis, Waseda Univ. (1993)
7
Dual Phase, LXe TPC

• Need single charge, photon sensitivity
• Use charge amplification instead
• of increasing ?E/kT.
• Good discrimination despite small number of e-, g
• Very good event location.
• A difficult technology

B.A.Dolgoshein, V.N. Lebedenko, B.U. Rodionov,
JETP Lett. 11 (1970) 513.
8
100 kg first design
9
Program

• Current focus - 10 kg full module
• Many RD prerequisities met
• Full dual phase TPC, discrimination of alphas
• Low threshold not yet demonstrated
• Nuclear recoil discrimination not demonstrated
• Have received 3 years funding for 10 kg module to
  run underground
• 100 kg module to follow

10
RD status

• Demonstrated
• Dual phase operation
• gt 1 m charge drift length
• UV sensitive PMTs operated in LXe
• Low activity measured ( 10 mBq/2" tube)
• Neutron beam scintiallation measurement underway
• PTR mechanical cooler
• MC background simulations
• Chromatographic separation of Kr and Xe
• In progress
• CsI photocathode with feedback supression
• Nuclear recoil ionization measurement,
  discrimination
• New HV distribution to PMTs
• Alternative light readouts
• MCP PMTs, GEMs, Wire gain, LAAPDs
• Kr removal to lt 100 ppt

11
Dual phase, small prototype

• Basic functionality demonstrated

12
Single-phase chamber
4.5kg

• Long electron drift demonstrated with
  recirculating purification.
• Hamamatsu R9288 PMT operated in liquid.
• Materials purity issue (custom divider in liquid)
• Blue LED Gain calibration

Xe Circulation
13
Stable running

• Drift lengths gt 1.2 m measured using online
  purification

14
Neutron beam scintillation calibration
15
10 Kg detector
16
Alpha/photon discrimination in 1.5 kg
Charge/Light
Alphas and photons
Charge

• Basic discrimination very powerful.
• Must lower current 100 keV light threshold.

Light
17
Primary light collection

• Simulation. (K. Ni, Columbia)
• Liquid xenon 23.7 eV / photon. 1 m attenuation
  length, n1.61
• PMTs 20 Q.E., 60 p.e. efficiency, quartz
  window - n1.56
• Teflon reflectivity 95

• Secondary light x-y position reconstruction
• Simple weighted sum 1.5 cm error (simulated)
• More sophisticated algorithms under development
• Now being tested.

18
Increasing light collection
Both options now being developed.
19
CsI photocathode

• Photons trapped by total internal reflection
  (n1.7).
• CsI photocathode a "perfect" match to this
  application
• VUV sensitive, "robust"
• Radioactivity negligible
• 20-fold improvement over current -gt 10 keV
  threshold for nuclear recoils.

• Feedback problem "Gate" grid. (Princeton)
• Commercial electronics switch 10 kV in lt 1 µs.
• Cross-talk to other grids, PMT
• 1 pF, 1 µS, 5000 V ? 5 mA, 5 nC.

20
Direct charge readout

• Motivation
• Radioactivity 10-3 of PMT readout
• x-y position readout presumably more robust
• PMT cost
• Requires CsI photocathode to work

21
GEMS, MCP PMTs

• GEMs (Rice) - electron readout
• Sub mm x-y readout possible
• Possible front-side CsI for additional light
  collection.
• Glue-free mounting method tested. LXe purity
  still under study

22
Radioactivity

• LXe a readily purifiable liquid or gas.
• Contrast Ge very pure, but not readily
  re-purified. Cosmogenics.
• No long lived Xe isotopes, except 136Xe
• 85Kr. t1/210.7y, b- 678 KeV. (Also 42Ar)
• Rn, Rn daughters. From emanation from
  components, welds.
• Particulates?
• Construction materials Cu, Teflon, Quartz. All
  very good. Wires ok with low mass.
• Neutrons. Ok at depth and with moderating
  shield.
• PMTs bad.
• but Hammatusu has made enormous progress.

23
(No Transcript)
24
Gamma Background from PMTs

• Brown group Monte Carlo
• Inner PMTs -- Hamamatsu 8778 (232Th/238U/40K/60Co)
  

PMTs
25
Hamamatsu PMTs
26
Final gamma background estimate

• Final background goal (1 "dru" 1
  event/kg/keVee/day)
• 10 kg detector 8 mdru (160 mdru for gammas)
• 100 kg detector 80 µdru (1.6 mdru for gammas)

27
Kr removal

• 85Kr. 687 keV endpoint b decay. Rate 280
  kBq/Kg(Kr).
• XENON100 need 0.1 ppb Kr/Xe.
• Industry (SpectraGas) can produce 10 ppb Kr/Xe.
• Chromatographic separation with activated
  charcoal
• Separation demonstrated with 60 gm charcoal
  column.

Xe
Kr
Kr separation 99.9 (Preliminary)

• Full processing system now being tested.
• Projected performance, 1 Kg charcoal column
• 1.8 Kg Xe/day
• Purification 103
• Use 14 stp m3 He/ Kg Xe processed.
• High purity system Summer 05.

28
Rn removal system developed for Borexino
29
Neutrons

• Negligible
• Neutrons from U, Th in rock
• Neutrons from µ in shield
• High energy neutron from muons in rock.
• 100 Kg goal 10 µdru is just met at Gran Sasso
  depth ( 3 µdru)
• SNOLAB is ideal for 1 ton experiment.

Aglietta et.al. Nuove Cimento 12, N4, page 467
30
Underground program

• 10 Kg module to be built in 2005
• Gran Sasso?
• "Standard" Pb/Poly/µ-veto shield
• 100 Kg module
• Single module - probably standard shield
• Shield details depend on detector performance
• Ton - scale
• 100 Kg modules
• Water shield
• 10 m Ø, 10 m high

31
Sensitivity of XENON
1 ton XENON projections

• Background free at 1 ton

32
End talk
33
Other physics

• Double beta decay with 136Xe
• Higher energy
• Very good energy resolution.
• Gain not allowed?
• EXO experiment (Stanford, SLAC, Alabama)
• p-p solar neutrinos.
• Similar energy range, backgrounds.
• But - no background rejection
• XMASS. (CLEAN).
• Possible that these can be done in single
  experiment, but more likely they are "kissing
  cousins".