Dark Matter Detection with Liquid Xenon Masahiro Morii Harvard University
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Transcript Dark Matter Detection with Liquid Xenon Masahiro Morii Harvard University
Dark Matter Detection
with Liquid Xenon
Masahiro Morii
Harvard University
Laboratory for Particle
Physics and Cosmology
21 August 2009
1
Dark Matter
Existence of Dark Matter is well established
from its gravitational effects
Coma cluster [Zwicky], Galaxy rotation curve [Rubin]
Weak gravitational lensing, Bullet cluster
Amount of Dark Matter is inferred from
cosmological data
~22% of the energy of the Universe
Local density 0.3 GeV/cm3
Identity of Dark Matter is unknown
Majority must be cold and non-baryonic
i.e. made of particles that are not a part of the SM
Dark Matter is a particle physics problem
as much as a cosmology problem
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WIMP Dark Matter
No shortage of candidates, but…
WIMPs are the front runners
~100 GeV new particles with weak
(and gravitational) interactions
Such a particle would naturally have
the right thermal relic density
Predicted in many BSM theories
(e.g. the LSP)
Since the annihilation cross section
s (c c Æ ff ) is constrained by the
relic density, we can predict:
s (c f Æ c f )
Direct detection
s (ff Æ c c )
Production at colliders
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Direct WIMP Detection
Best limits on the WIMP-nucleon
cross section are ~5x10-44 cm2
CDMS : Ge and Si crystals at 10
mK,
121 kg-day exposure
XENON10 : liquid Xe, 136 kg-day
For LSPs, the interesting region
is around 10-44 cm2
Smaller cross sections possible, but
increasingly difficult to reconcile with
the flavor problem
Next generation of experiments
aim for <10-45 cm2
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Liquid Xenon
WIMP-nucleus cross section ∝ A2
Xe (A = 131.3) gives high signal rate
100 kg-year exposure can probe
(WIMP-p) < 10-45 cm2
Key liquid Xe properties
High density: 3 g/cm3
High boiling point: 165K
Good scintillator: 42 photons/keV
High ionization yield: W = 15.6 eV
= 175 nm easy to detect with PMTs
High electron mobility, low diffusion
No long-lived radioactive isotopes besides double-beta decays
85Kr
must be removed by charcoal chromatography
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Two-Phase Xe Detector
PMTs collect prompt (S1) and
proportional (S2) light signals
S1-S2 delay Drift length
S2 light pattern Horizontal location
S2/S1 ratio differs markedly
between electron and nuclear recoil
>98.5% rejection of EM backgrounds
Good scaling to larger masses
1 m3 holds 3 tonnes
Instrumentation ∝ (mass)2/3
Backgrounds improve with size due to
self shielding
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LUX Experiment
LUX is a 350 kg (100 kg fiducial)
liquid Xe experiment
Located in the Davis cavern, Sanford
Underground Lab in Homestake, SD
XENON10 technology has been
improved to achieve <1 bkgd. in
100 kg-year
Xe purification system has 300 kg/day
throughput using a heat exchanger
Ultra-low activity Ti vacuum vessel replaces SS + Cu
PMTs have low activity (9/3 mBq of U/Th per tube) and high QE (27%)
183 m3 purified water tank shields the detector from neutrons
Recoil energy threshold <5 keV
(WIMP-p) = 5x10-46 cm2
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LUX Collaboration
Brown, Case Western, LBNL, Harvard,
LLNL, Maryland, Texas A&M, Rochester,
South Dakota, Yale
Funded by DOE & NSF
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Harvard Group
Harvard joined LUX in June 2009
Morii (50%) is the PI
Took up a critical-path item: post-amplifier
preamp
PMT
120 channels of receiver-amplifier-shaper for the PMT signals
Full system is needed in November
postamp
Harvard took over production from UC Davis
Recruiting a postdoc and 1–2 graduate students
Will take part in detector integration, commissioning
Develop analysis software framework
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Analog Trigger
Digital Trigger
FADC
Oliver and Morii improved the LLNL design
New LPPC engineer, Meghna Kundoor, working on testing
Components in hand. PC boards in fabrication
On track for November delivery
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LUX Status and Schedule
Prototype LUX0.1 is operating at Case
1 liter of liquid Xe viewed by 4 PMTs
Test cryogenics and Xe purification system
>1 m electron drift achieved in 3 days
Assembly of LUX in Sanford surface
building will start in November
All major components are in hand
Building is being fitted out
Fully-assembled LUX lowered to
Davis cavern (4,850 ft) in Spring
2010
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Dark Matter
Dark Matter search will start!
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LZ Proposal
LZ = LUX scaled up to 1500 kg (1200 kg fiducial)
Joint collaboration of LUX and ZEPLIN-III
LUX infrastructure designed to accommodate LZ
(WIMP-p) = 2x10-47 cm2 in 2 years
2000-fold improvement over current limits
Cost of liquid Xe ~$1000/kg
Maximize the fiducial/total mass ratio by rejecting
single-scatter -ray background with liquid scintillator
Harvard will assume larger responsibilities
Development of low radioactivity, high-QE PMT
Complete analog electronics chain (pre + postamp)
MRI-R2 proposal submitted this month
3-year construction Data taking in 2013
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Summary and Prospect
Exciting time for Dark Matter detection
Cosmology points us to compelling particle physics
Liquid Xe technology has the potential for first observation
Harvard is entering DM hunting with strong commitment
Producing critical component for the LUX experiment
PMTs and analog electronics for the proposed LZ experiment
Discovery potential of LUX is excellent
(WIMP-p) = 5x10-46 cm2 covers the SUSY-favored region
Dark Matter search run will start in 2010
LZ will push the sensitivity to 2x10-47 cm2 by 2015
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