LUX: A Large Underground Xenon detector WIMP Search Mani...
Transcript of LUX: A Large Underground Xenon detector WIMP Search Mani...
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May 5, 2007 Mani Tripathi, INPAC Meeting
LUX: A Large Underground Xenon
detector
WIMP Search
Mani Tripathi
INPAC Meeting
Berkeley, May 5, 2007
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May 5, 2007 Mani Tripathi, INPAC Meeting
New Collaboration
Groups formerly in XENON10:
Case Western, Brown, Livermore Natl. Lab
(major fraction of the US contingent in XENON10)
Groups from ZEPLIN II:
UCLA, Texas A&M, Rochester
(entire US contingent in ZEPLIN-II)
New Entrants:
UCDavis, LBNL
(background in neutrinos/nuclear/HEP)
INPAC is a large fraction of this effort.
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May 5, 2007 Mani Tripathi, INPAC Meeting
NaI, Xe,
Ar, Ne
Direct Detection Techniques
CRESST I
CDMS
EDELWEISS
CRESST II
ROSEBUD
ZEPLIN II, III
XENON
LUX
WARP
ArDM
SIGN
NAIAD
ZEPLIN I
DAMA
XMASS
DEAP
Mini-CLEAN
DRIFT
IGEX
COUPP
Scin
tillatio
nH
eat -
Phonons
Ionization
Ge, Si
Al2O3, LiF
CaWO4, BGO
ZnWO4, Al2O3 …
Xe, Ar,
Ne
Ge, CS2, C3F8
~100%
of
En
erg
y
~20% of Energy
Few
% o
f Energ
y
Fig. courtesy
H. Sobel
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May 5, 2007 Mani Tripathi, INPAC Meeting
Noble Liquids as Target
WIMP flux on earth: v ~ c/1000, mc ~ 100 mproton
flux ~ 105 /(cm2 s)
!
" =" protonµ2A2
(! = reduced mass)
Scatter coherently from whole nucleus:
Scatter on nuclei:For Xe, useful range is5Kev<Recoil Energy <50 KeV
Erecoil
Ra
te fo
r E
> E
recoil
(events
/Kg/d
ay)
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May 5, 2007 Mani Tripathi, INPAC Meeting
ZEPLIN-II
Jan 2007
! < 6.6 x 10-43 cm2
@ m= 65 GeV
Liquid Xenon has come out with results in 2007
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May 5, 2007 Mani Tripathi, INPAC Meeting
10 kg fiducial dual
phase xenon detector
with only 60 days data
CDMS
2004+05
Dramatic Improvement in DM Sensitivity
XENON10
April 2007
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May 5, 2007 Mani Tripathi, INPAC Meeting
EGC
Cathode
Grid
Anode
EAG
EAG > EGC
Liquid phaseLiquid phase
Gas phaseGas phase
PMT Array
(not all tubes shown)
Light SignalLight Signal
UV ~175 nmUV ~175 nm
photonsphotons
TimeTime
PrimaryPrimary
SecondarySecondary
Interaction (WIMP or Electron)Interaction (WIMP or Electron)
Liq. Surface
ee--ee--
ee--ee--
ee--ee--
ee--ee--
ee--ee--
ee--ee--
Electron Drift
~2 mm/!s
0–150 !s
depending on
depth
~40 ns width
~1 !s width
Two Signal Technique
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May 5, 2007 Mani Tripathi, INPAC Meeting
Xenon Facts
Ionization in liquid:
• About one electron-ion pair /15 eV ofdeposited energy
175 nm Scintillation:
• About one photon/20 eV of depositedenergy
• Ionization/Scintillation ratiochanges with interaction type
Ion pairs more likely to recombine in thedense tracks generated by nuclearinteractions
• A strong anti-correlation betweenionization and scintillation
90%
10%
Ionization signal
Scintillation signal
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May 5, 2007 Mani Tripathi, INPAC Meeting
WIMP or
Neutron
nuclear
recoil
electron
recoil
Gamma or
Electron
Nuclear recoil:
Electrons recombine
in the liquid due to
higher ionization
density
- fewer primary electrons
Also overall quenching
of scintillation relative
to electron recoil
Gamma recoil:
Less recombination
in the liquid due to
lower ionization density
more primary electrons
Ionization/Scintillation Response
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May 5, 2007 Mani Tripathi, INPAC Meeting
Realization of Two Signal Technique
Electromagnetic recoils
Neutron recoils:
WIMPs would appear
here
Example from XENON10:
Plot Log (S2/S1)
versus
total recoli energy.
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May 5, 2007 Mani Tripathi, INPAC Meeting
The LUX detector and shield
~ 6m diameter Water Cerenkov shield (low cost) Tall dual phase detector
Aspect ratio = 1.5
100 kg100 kg
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May 5, 2007 Mani Tripathi, INPAC Meeting
LUX Parameters•300 kg Dual Phase liquid Xe TPC with 100 kg fiducial
– >99% ER background rejection for 50% NR acceptance, E>10 keVr
3D-imaging TPC eliminates surface activity, defines fiducial
•Backgrounds:
–Internal: strong self-shielding of PMT activity
• "/# < 7x10-4 /keVee/kg/day, from PMTs (Hamamatsu R8778 or R8520).
•Neutrons ($,n) & fission subdominant
–External: large water shield with muon veto.
•Very effective for cavern "+n, and HE n from muons
•Very low gamma backgrouns 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.
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May 5, 2007 Mani Tripathi, INPAC Meeting
Active Water Shield and Veto
Veto on incoming muons via
Cherenkov light signal.
Tag thermalized neutrons
generated within the detector
• Gd (0.2%) in water gives a
capture efficiency of
> 90% for thermal neutrons,
followed by an 8 MeV gamma
cascade
Incident n
Xe recoil%" ~ 8 MeV
Gd
! ~ 50 µsn captures on Gd
Xe detector Water shield
Studies for SuperK have shown compatibility with standard detector materials(Bob Svoboda et al)
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May 5, 2007 Mani Tripathi, INPAC Meeting
LUX Dark Matter Goal
LUX - Sensitivity curve at2x10-45 cm2 (100 GeV)
•Exposure: Gross Xe Mass 300 kgLimit set with 120 days runningx 100 kg fiducial mass x 50% NRacceptance
~1 background event duringexposure assuming mostconservative assumptions ofER 7x10-4 /keVee/kg/day and 99%ER rejection
–ER bg assumed is dominated byguaranteed Hamamatsu PMTbackground. Improvements in PMTbg (and rejection power) will extendbackground free running period, andDM sensitivity
Edelweiss IZEPLIN II
CDMS IIWARP
LUX (Proj)SuperCDMS@Soudan
SuperCDMS@SNOLab
Comparison -- SuperCDMS Goal @
SNOLab: Gross Ge Mass 25 kg
(x 50% fid mass+cut acceptance)
Limit set for 1000 days running x
7 SuperTowers
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May 5, 2007 Mani Tripathi, INPAC Meeting
Status
Proposal Under review by NSF/DoE.
Meanwhile, LUXCore
The collaboration is fully active –
Technical VideoCons every
Week … Construction activity in full
swing at all institutions using Univ
resources, startup seed funds etc.
Construction finished late
Summer 07 -- operations at
Case: Fall 2007.
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May 5, 2007 Mani Tripathi, INPAC Meeting
LUX program: exploit scalability
•LUXcore: Final engineering for large-scaledetector
–Cryostat, >100 kV feedthrough, charge drift,light collection over large distance
–Full system integration, including ~1m watershield
–40 kg narrow “core”, 14 PMTs, 20 cm Ø x 40cm tall.
•Radial scale-up requires full-funding.
LUX detector
LUXcore
Very good match to early-implementaion DUSEL
SNOLAB LOISystem scalable to very large mass.
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May 5, 2007 Mani Tripathi, INPAC Meeting
Cryostat Being Installed
At Case.