Transcript WIMP search results from ZEPLIN II and XENON10 and T. Shutt

WIMP search results from ZEPLIN II and XENON10
and
the race to detect dark matter with noble liquids
T. Shutt
Case Western Reserve University
T. Shutt, PPC07, 5/17/2007
Detecting galactic WIMP dark matter
Dark matter “Halo” surrounds all galaxies, including ours.
Density at Earth:
 
300
mproton liter
mwimp ~ 100 mproton.
3 WIMPS/liter!
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Typical orbital velocity:
v ≈ 230 km/s
~ 1/1000 speed of light
Coherent scalar interactions: A2
Rate: < 0.06 event/kg/day, or much lower
T. Shutt, PPC07, 5/17/2007
Detecting rare events.
• Problem: radioactivity
—
—
Ambient: 100 events/kg/sec.
Pure materials in detector
•Shield against outside backgrounds
•Underground to avoid muons
µ
Why Roman lead is special.
U, Th in rock: 2 ppm ≈ 107 decays/day/kg
detector
Crude smelting removes U, Th from Pb.
210Pb
WIMP
T. Shutt, PPC07, 5/17/2007
at bottom of U decay chain remains.
T1/2= 22 years
The kilogram is not the right scale.
J. Ellis, A. Ferstl, K. Olive, Phys.Lett. B481 (2000) 304-314
QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture.
≈ 10 tons Xe
Spin dependent couplings
Spin independent couplings
QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture.
QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture.
T. Shutt, PPC07, 5/17/2007
4
Massive detectors for solar neutrinos
scintillator
water
BOREXINO: 1000 tons of ultra-pure (10-16 g/g U, Th) scintillator,
T. Shutt, PPC07, 5/17/2007
2000 PMTs.
Photo: during filling, 1/27/07
Two approaches to low backgrounds
• Better living through physics: sophisticated
detectors:(CDMS)
• Better living through chemistry: pure, large detectors:
(Borexino)
• Can we get best of both?
—
—
Mass
Highly specific, sophisticated event information.
T. Shutt, PPC07, 5/17/2007
• Liquid target:
—
—
Liquid Noble-Gas Detectors
Readily purified
Scalable to large masses
• Liquid scintillator:
—
—
14C
fatal for dark matter
Even in petroleum - 10-18
14C: U->a + rock -> n -> 14N(n,p)14C
• Liquid noble gasses.
—
—
—
Easily purified.
Scintillation and Ioinization
Cryogenic PMTs exist.
Xe: 165 K,  =175 nm
• Ar: 87.3 K,  =128 nm, 39Ar - 1 Bq/kg.
• Ne: 27.1 K,  =80 nm, bubbles -> slow charge drift
•
• Challenge: small signals
—
—
—
Nex=E/W, WGe ≈ 3 eV, WXe ≈ 15 eV
Cryogenic: E/kT maximized with T ~ 0.020 K
Rare gasses: High voltage boosts E (e.g., in PMT)
T. Shutt, PPC07, 5/17/2007
Scalable to large masses
Single Phase detectors
XMASS: 800kg
Xe
Rayleigh scattering - position
information poor: need large
detectors to avoid surface
events.
Current XMASS: 100 kg,
limited by edge events.
DEAP/CLEAN
Excimer molecule has
singlet (fast) and triplet
(slow) states:
discrimination in Ar, Ne.
Ar: need 108
discrimination!
T. Shutt, PPC07, 5/17/2007
Nuclear recoils
Electron recoils
Dual phase time projection chamber
PMTs
Time
-
Es
~1 µs width
5 µs/cm
• Can measure single electrons and
photons.
• Charge yield reduced for nuclear
recoils.
• Good 3D imaging
—
Eliminating edges crucial.
T. Shutt, PPC07, 5/17/2007
Primary
~40 ns width
---
LXe
Ed
WIMP
A. Bolozdynya, NIMA 422 p314 (1999).
Discrimination based on recombination
• Recombination turns charge into light
• Dense nuclear recoils (WIMP signal):
high recombination
• Less-dense electron recoils (most
background): lower recombiantion
(Nigel Smith, RAL)
T. Shutt, PPC07, 5/17/2007
Charge (S2) and light (S1) discrimination:
Basic behavior
Neutron source
Electron recoils
Nuclear
recoils
T. Shutt, PPC07, 5/17/2007
40 keV inelastic from
neutrons
Gamma source
Electron recoils
ZEPLIN-II Detector
• 5 months continuous operation
• 1.0t*day of raw DM data
T. Shutt, PPC07, 5/17/2007
LXe
140 mm
~75 s
S2
GXe
S1
E
12
ZEPLIN II - WIMP search data
•31 live days running, 225 kg-days
exposure
Red
Box is 5-20keVee, 50% NR acceptance
based on neutron calibration
29 candidate events seen
•Estimate 50% from ER leakage from upper band
•Other 50% from lower band which are RAdon
daughters plating on PTFE side walls
Both
populations have been modeled and
subtraction performed
Final results is <10.4 events (90% CL)
consistent with WIMP
T. Shutt, PPC07, 5/17/2007
The XENON10 Collaboration
Columbia University Elena Aprile, Karl-Ludwig Giboni, Sharmila Kamat, Maria Elena Monzani,
Guillaume Plante, Roberto Santorelli and Masaki Yamashita
Brown University Richard Gaitskell, Simon Fiorucci, Peter Sorensen and Luiz DeViveiros
RWTH Aachen University Laura Baudis, Jesse Angle, Joerg Orboeck, Aaron Manalaysay and
Stephan Schulte
Lawrence Livermore National Laboratory Adam Bernstein, Chris Hagmann, Norm Madden
and Celeste Winant
Case Western Reserve University Tom Shutt, Peter Brusov, Eric Dahl, John Kwong and
Alexander Bolozdynya
Rice University Uwe Oberlack, Roman Gomez, Christopher Olsen and Peter Shagin
Yale University Daniel McKinsey, Louis Kastens, Angel Manzur and Kaixuan Ni
LNGS Francesco Arneodo and Alfredo Ferella
Coimbra University Jose Matias Lopes, Luis Coelho, Luis Fernandes and Joaquin Santos
T. Shutt, PPC07, 5/17/2007
XENON10 detector
•22 kg of liquid xenon
•15
kg active volume
•20 cm diameter, 15 cm drift
•Hamamatsu R8520 1’’×3.5 cm PMTs
•bialkali-photocathode
Rb-Cs-Sb,
•Quartz window; ok at -100ºC and 5 bar
•Quantum efficiency > 20% @ 178 nm
•48 PMTs top, 41 PMTs bottom array
•x-y
position from PMT hit pattern; σx-y≈ 1 mm
•z-position from ∆tdrift (vd,e- ≈ 2mm/µs), σZ≈0.3
mm
•Cooling: Pulse Tube Refrigerator (PTR),
•90W, coupled via cold finger (LN2 for
emergency)
T. Shutt, PPC07, 5/17/2007
XENON 10: Underground at LNGS
We are here
T. Shutt, PPC07, 5/17/2007
XENON10 live time at Gran Sasso
Blind WIMP
Search DAta
nonblind
WIMP
Search
Data
T. Shutt, PPC07, 5/17/2007
92% live
high stats
calibrations
XENON10 Events
Example: Low Energy Compton Scatter
• S1=15.4 phe ~ 6 keVee
Incident Particle
• Drift Time ~38 μs => 76 mm
s1: Primary Scintillation Created by
Interaction LXe
s2: Secondary Scintillation Created by eextracted & accelerated in GXe
e- eee- e-
s2
e- e- e- e-
s1
E = 1kV/cm
(s2/s1)ER > (s2/s1)NR
Expect > 99% rejection efficiency of
/n Recoils…
Reduction of Backgrounds =>
Reduction of Leakage Events
T. Shutt, PPC07, 5/17/2007
18
In-situ calibrations
Nuclear recoil spectrum
MC
Data
T. Shutt, PPC07, 5/17/2007
19
“Partial” multiple scatter background
Pre cut
After S1 hit
pattern cut
• Cut on disagreement between
S1-derived position, and TPCderived position.
T. Shutt, PPC07, 5/17/2007
20
High efficiency for nuclear recoils
• Threshold: 2 keVee /
4.5 keVr - S1
efficiency > 99%
Single Scatter Neutron data in Fiducial
Effect of adding QC2 cut
• Total cuts efficiency:
95% to 78% in WIMP
window (2-12 keVee)
100%
Single Scatter Neutron data in Fiducial
Acceptance of QC2 cut for single NR
T. Shutt, PPC07, 5/17/2007
2 keVee
12 keVee
21
XENON10 WIMP search data
• Blind Analysis
• 58.6 days, 5.4 kg
fiducial
• ~50% acceptance of
Nuclear Recoils
• 2-12keVee / 4.5-27
keVr
Assuming QF 19% 4.5-27
keVr
• 10 events in the “box”
after all primary analysis
blind cuts
—
—
log( S2 / S1 )
—
“Straightened ER Scale”
Text
Calibration expectation:
7.0 +2.1-1.0 (gaussian)
Data: 5 ~gaussian;
5 non-gaussian
2 - 12 keVee
4.5 - 27 keVr @ QF 19%
“Leakage” Events
S1
T. Shutt, PPC07, 5/17/2007
22
Discrimination: best at lowest energy!
Close agreement between 40
gm prototype (Case) and
XENON10 (10 kg)
Low threshold + good
discrimination: Xe very sensitive to
dark matter.
T. Shutt, PPC07, 5/17/2007
Physical limits to discrimination
• Recombination fluctuations, instrumental effects can be
separated for (higher energy) lines.
• Light collection statistics estimated by Monte Carlo
• ~99.9% looks to be hard limit set by Xe physics
T. Shutt, PPC07, 5/17/2007
(2.2 phe/keVee)
XENON10, ZEPLINII results
(XENON10 curve: no background subtraction)
T. Shutt, PPC07, 5/17/2007
25
How do we go to very large scale?
T. Shutt, PPC07, 5/17/2007
LUX Dark Matter Experiment
Brown - Gaitskell
Case - Shutt, Bolozdynya
LLNL - Bernstein
LBNL - Lesko
Rochester - Wolfs
Texas A&M - White
UC Davis - Tripathi, Svoboda
UCLA - Wang, Cline, Arisaka
• Dark matter
experiments:
—
CDMS, ZEPLIN II,
XENON10
• Solar, reactor, atm.
neutrinos:
—
SNO, IMB, SuperK,
Kamland, Borexino
• High energy
physics
T. Shutt, PPC07, 5/17/2007
•300 kg total, 100 kg fiducial
detector.
•Water shield
•DM reach: 2x10-45 cm2 in
4 months
—Very
conservative background
assumptions
—Possibly ~5x10-46 cm2 with longer
running.
•Allows discovery at ~10-45 cm2.
27
Primary background: Single-scatter gammas
• Simple background problem.
—
—
Single, low-energy Compton scattering
Very forward peaked.
• Rare, because of energetics.
• Can approximate analytically:
—
Probability of n scatters while traversing
distance L:
1 L   
Pn (L)    e
n!  
n
L
Confirms Monte Carlo
T. Shutt, PPC07, 5/17/2007
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, but
T. Shutt, PPC07, 5/17/2007
Neutron Background
• PMT (alpha,n) and fission neutrons - potential, but sub-dominant
background
• Multiple scatter powerfully defines clean fiducial volume.
—
—
Is primarily question of fiducial mass: lower background allows larger
fiducial mass
Relative importance decreases as detector mass increases.
T. Shutt, PPC07, 5/17/2007
Large-scale water shield
• Lowest-known
background shielding
material
—
Naively ~ 10,000 cleaner
than Pb/Cu.
• Very effective for high
energy neutrons
—
1 m: difference betweeen
Homestake and SNOLAB
20 cm Pb
• Very economical
—
10m, multi-experiment
shield:
(Gaitskell/DeViveros)
$50 K commerical
water purification
• $100 K for water tank
•
T. Shutt, PPC07, 5/17/2007
31
Pre-DUSEL Homestake possibility
1.75 m
14 m
16 m
• DUSEL process for new national underground lab.
• 4850 mwe depth at Homestake - early program.
• 10 module system
• 4 m shielding
• 5/17/2007
Davis cavern +3m depth.
T. Shutt, PPC07,
100 kV Icarus HV feedthrough
T. Shutt, PPC07, 5/17/2007
33
T. Shutt, PPC07, 5/17/2007
34
Installed at Case - 5/17/07, 11 am.
T. Shutt, PPC07, 5/17/2007
Surface integration and
testing
35
LUX deliverable for 2009
T. Shutt, PPC07, 5/17/2007
Guaranteed discovery potential:
~7 WIMPs per month at 1x10-44 cm2 (1x10-8 pb)
36
Fine
SUSY
Theory
Models
T. Shutt, PPC07, 5/17/2007
Charge and light yield phenomena
Charge yield - nuclear recoils
Case, Columbia+Brown
Qui ckTime™ and a TIFF (LZW) decompressor are needed to see thi s pi ctur e.
Aprile et al., astroph/0601552, submitted to
PRL
Wph
-1
zero
field
zero recombination
T. Shutt, PPC07, 5/17/2007
W-1 W0-1
A Recombination-Independent Energy Scale
(Case) Scintillation-based Energy Scale
Recombination Independent Energy Scale
electron recoil
band
40 keV inelastic
nuclear recoil band
122 keV gamma line
• Assume electron-photon anti-correlation is exact:
E = W0  (ne- +n)
• Improved linearity
• Improved resolution. At 122 keV:
—
—
—
—
T. Shutt, PPC07, 5/17/2007
Light: 16% (/ )
Charge: 10%
Summed: 5.7%
Uncorrelated sum would be 8.6%
•Does not improve discrimination
Field Dependence
• Electron recoils
are field
dependent
• Nuclear recoils
are not, very
•But… ER field dependence
disappears in WIMP range
T. Shutt, PPC07, 5/17/2007
Kr removal
•
85Kr
—
—
- beta decay, 687 keV endpoint.
Goals for 10, 100, 1000 kg detectors: Kr/Xe < 1000, 100, 10 ppt.
Commercial Xe (SpectraGas, NJ): ~ 5 ppb (XMASS)
Kr
recovery
10 Kg-charocoal column
system at Case
feed
purge
• Chromatographic separation on charcoal column
Cycle: > 1000 separation
Xe
200 g/cycle, 2 kg/day
25 Kg purifed to < 10 ppt
T. Shutt, PPC07, 5/17/2007
Cuts Explanation
see Guillaume Plante, Columbia, APS Talk
T. Shutt, PPC07, 5/17/2007
42