1. LUX: Shedding Light on Dark Matter
Adam Bradley
Case Western Reserve University
Great Lakes Cosmology Workshop 8
June 2, 2007

2. Outline Give outline Give talk End talk Answer (easy) questions Basics
Galactic WIMP DM / general rare events detection
Liquid noble-gas detectors
TPCs and scaling LXe
Current DM sensitivities
LUX in all its glory
Give talk
End talk
Answer (easy) questions
January 15, 2019
A. Bradley; GLCW8, the OSU

3. The Basics Fritz Zwicky, Vera Rubin, et al… WMAP, SDSS, etc…
Weak scale energies
SUSY - neutralino
January 15, 2019
A. Bradley; GLCW8, the OSU

4. Rate: < 0.06 event/kg/day, or much lower
Detecting galactic WIMP dark matter
Dark matter “Halo” surrounds all galaxies, including ours.
ρ ∼ 300
mproton
liter
Density at Earth:
mwimp ~ 100 mproton.
3 WIMPS/liter!
Typical orbital velocity:
v ≈ 230 km/s
~ 1/1000 speed of light
Coherent scalar interactions: A2
Rate: < event/kg/day, or much lower
January 15, 2019
A. Bradley; GLCW8, the OSU

5. Detecting rare events. µ Shield against outside backgrounds
Problem: radioactivity
Ambient: 100 events/kg/sec.
Pure materials in detector
Shield against outside backgrounds
Underground to avoid muons
WIMP
detector
January 15, 2019
A. Bradley; GLCW8, the OSU

6. Liquid Noble-Gas Detectors
Liquid target:
Readily purified
Scalable to large masses
Liquid scintillator: 14C fatal for dark matter
Even in petroleum
14C: U->a + rock -> n -> 14N(n,p)14C
Liquid noble gasses.
Easily purified.
Scintillation and Ioinization
Cryogenic PMTs exist.
Xe: 165 K, λ=175 nm
Ar: 87.3 K, λ =128 nm, 39Ar - 1 Bq/kg.
Ne: 27.1 K, λ =80 nm, bubbles -> slow charge drift
Scalable to large masses!
January 15, 2019
A. Bradley; GLCW8, the OSU

7. Dual phase time projection chamber
PMTs
LXe
WIMP
Time
Primary
5 µs/cm
~40 ns width
~1 µs width - Ed Es -
Can measure single electrons and photons.
Charge yield reduced for nuclear recoils.
Good 3D imaging
Eliminating edges crucial.
A. Bolozdynya, NIMA 422 p314 (1999).
January 15, 2019
A. Bradley; GLCW8, the OSU

8. Scaling liquid Xe to large masses
Predictions from analytical calculation
Enormous gains from self shielding above ~ 100 kg
For very large mass, reduction in background, or increase in discrimination increases fiducial fraction
January 15, 2019
A. Bradley; GLCW8, the OSU

9. Current Dark Matter Sensitivities
Edelweiss I
ZEPLIN II
CDMS II
WARP
LUX (Proj)
XENON10
[070400]
We have entered phase of testing SUSY.
Need ton-scale detectors for full “generic” test.
January 15, 2019
A. Bradley; GLCW8, the OSU

10. LUX Dark Matter Experiment - Summary
Brown, Case, LLNL, LBNL, Rochester, Texas A&M, UC Davis, UCLA
XENON10, ZEPLIN II (US) and CDMS; ν Detectors (Kamland/SuperK/SNO/Borexino); HEP/γ-ray astro
(Also ZEPLIN III Groups after their current program completed)
300 kg Dual Phase LXe TPC with 100 kg fiducial
>99% ER background rejection for 50% NR acceptance, E>10 keVr
(Case+Columbia/Brown Prototypes + XENON10 + ZEPLIN II)
3D-imaging TPC eliminates surface activity, defines fiducial
Backgrounds:
Internal: strong self-shielding of PMT activity
γ/β < 7x10-4 /keVee/kg/day, from PMTs (Hamamatsu R8778 or R8520).
Neutrons (α,n) & fission subdominant
External: large water shield with muon veto.
Very effective for cavern γ+n, and HE n from muons
Very low gamma backgrounds with readily achievable <10-11 g/g purity.
DM reach: 2x10-45 cm2 in 4 months
Possible ~5x10-46 cm2 reach with recent PMT activity reductions, longer running.
January 15, 2019
A. Bradley; GLCW8, the OSU

11. LUX program: exploit scalability
LUX detector
LUXcore
LUXcore: Final engineering for large-scale detector
Cryostat, >100 kV feedthrough, charge drift, light collection over large distance
Full system integration, including ~1m water shield
40 kg narrow “core”, 14 PMTs, 20 cm Ø x 40 cm tall.
Radial scale-up requires full-funding.
Under construction; operations at Case: summer 2007.
LUX Experiment
LUX in ~ 6m Ø water shield
Very good match to early-implementaion DUSEL (e.g., Homestake “Davis” cavern)
System scalable to very large mass.
January 15, 2019
A. Bradley; GLCW8, the OSU

12. Summary The search for WIMP DM is on and heating up!
Use of liquid noble-gas detectors gaining momentum
“Easy” to use and scale
LUX is here!
“Let there be light (on WIMP DM)!”
January 15, 2019
A. Bradley; GLCW8, the OSU