the xenon10 dark matter search
DESCRIPTION
The XENON10 dark matter search. T. Shutt Case Western Reserve University. The XENON10 Collaboration. Columbia University Elena Aprile (PI), Karl-Ludwig Giboni , Sharmila Kamat, Maria Elena Monzani , , Guillaume Plante*, and Masaki Yamashita Brown University - PowerPoint PPT PresentationTRANSCRIPT
T. Shutt, SNOLAB, 8/22/6 1
The XENON10 dark matter search
T. Shutt
Case Western Reserve University
T. Shutt, SNOLAB, 8/22/6 2
Columbia University Elena Aprile (PI), Karl-Ludwig Giboni, Sharmila Kamat,
Maria Elena Monzani, , Guillaume Plante*, and Masaki YamashitaBrown University
Richard Gaitskell, Simon Fiorucci, Peter Sorensen*, Luiz DeViveiros*University of Florida
Laura Baudis, Jesse Angle*, Joerg Orboeck, Aaron Manalaysay* Lawrence Livermore National Laboratory
Adam Bernstein, Norm Madden and Celeste WinantCase Western Reserve University
Tom Shutt, Adam Bradley, Paul Brusov, Eric Dahl*, John Kwong* and Alexander BolozdynyaRice University
Uwe Oberlack , Roman Gomez* and Peter ShaginYale University
Daniel McKinsey, Richard Hasty, Angel Manzur*, Kaixuan NiLNGS
Francesco Arneodo, Alfredo Ferella*Coimbra University
Jose Matias Lopes, Luis Coelho*, Joaquim Santos
The XENON10 Collaboration
T. Shutt, SNOLAB, 8/22/6 3
Promise of liquid Xenon.• Good WIMP target.
• Readily purified (except 85Kr)
• Self-shielding - high density, high Z.
• Can separate spin, no spin isotopes129Xe, 130Xe, 131Xe, 132Xe, 134Xe, 136Xe
• ~ Low-background PMTs available
• Rich detection media— Scintillation— Ionization— Recombination discriminates between
electron (backgrounds) and nuclear (WIMPs, neutrons) recoils
Scalable to large masses
T. Shutt, SNOLAB, 8/22/6 4
LXe
PMTs
A. Bolozdynya, NIMA 422 p314 (1999).
WIMP
XENON: Dual Phase, LXe TPC “Calorimeter”
5 µ
s/cm
~1 µs
---
-
Ed
Es
Tim
eT
ime
~40 ns
• Very good 3D event location.• Background discrimination based
on recombination
XENON Overview• Modular design: 1 ton in ten 100
kg modules.
• XENON10 Phase: 15 kg active target in Gran Sasso Lab as of March, 2006. Shield under construction. Physics runs start: June 2006.
• XENON100 Phase: design/construction in FY07 and FY08 ($2M construction). Commission and undeground start physics run with 2008.
T. Shutt, SNOLAB, 8/22/6 5
Scintillation Efficiency of Nuclear Recoils
p(t,3He)n
Borated Polyethylene
Lead
LXe
L ~ 20 cm
BC501AUse pulse shape discrimination and ToF to identify n-recoils
Columbia RARAF2.4 MeV neutrons
Columbia and Yale
Aprile et al., Phys. Rev. D 72 (2005) 072006
T. Shutt, SNOLAB, 8/22/6 6
Nuclear and electron recoils in LXe
ELASTIC Neutron Recoils
INELASTIC 129Xe40 keV + NR
INELASTIC 131Xe80 keV + NR
137Cs source
Upper edge -saturation in S2
AmBe n-sourceNeutron
ELASTIC Recoil
5 keVee energy threshold = 10 keV nuclear recoil
Columbia+Brown
Case
T. Shutt, SNOLAB, 8/22/6 7
Charge and light yields
QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.
recombination less
more
Wph-1
zero field
W0-1W-1
zero recombination
Aprile et al., astro-ph/0601552, submitted to PRL
Columbia+Brown; Case
Charge yield - nuclear recoils
T. Shutt, SNOLAB, 8/22/6 8
Recombination fluctuations
• Recombination independent energy: E = W0 (ne- +n)— Improves energy resolution— Restores linearity.
• Recombination fluctuations fundamental issue for discrimination.• New energy definition itself cannot improve discrimination
40 keV (n–inelastic)
Neutron Recoils
CaseScintillation-based energy Combined energy
T. Shutt, SNOLAB, 8/22/6 9
Discrimination at low energy
• Charge yield increase for BOTH nuclear recoils and electron recoils at low energy.
• E> 20 keVr: recombination fluctuations dominate.
• Monte Carlo:— >~99% discrimination at 10 keVr.
This is value used in XENON10/100/1T proposals
Electron recoil dataNuclear recoil data
(Case)
Electron Recoil Band
Centroid
Nuclear Recoil Band
Centroid
99% Rejection (MC)
Nuclear Recoil Event: 5 keVr
See: T.Shutt, et al., astro-ph/0608137
Some comments on Ar and Xe: atomic physics surprises• Xe:
— Drop in recombination for low energy nuclear recoils
— Energy independence of nuclear recoil recombination.
— Drop in recombination for very low energy electron recoils
LAr LXe
• Xe scintillation discrimination: a cautionary tale
(Yale)
LAr
nr
er
• Ar: — Huge pulse-shaped discrimination needed
because of 39Ar.— Very small apparent “Lindhard” factor.
T. Shutt, SNOLAB, 8/22/6 11
“S2” signalXY Position Reconstruction in 3 kg prototype
• Chisquare estimate from Monte Carlo - generated S2 map
122 keV (57Co)
Reconstructed edge events at 122 keV
Resolution ≈ 2 mm.
Neutron Elastic Recoil
40 keV Inelastic (129Xe)+ NR
80 keV Inelastic (131Xe)+ NR
Neutron Elastic Recoil
40 keV Inelastic (129Xe)+ NR
80 keV Inelastic (131Xe)
110 keV inelastic
(19F)+ NR
5 mm radial cut reduces gamma events in nuclear recoils region.
T. Shutt, SNOLAB, 8/22/6 12
LXe Active
PMTs (top 48)
Pulse tube cryocooler
PMTs (bottom 41)
Gas Region
XENON10: Cryostat Assembly
Vacuum Cryostat
Re-condenser
T. Shutt, SNOLAB, 8/22/6 13
LN Emergency Cooling Loop
XENON10: Detector Assembly
89 Hamamatsu R5900 (1” square)20 cm diameter, 15 cm drift length22 kg LXe total; 15 kg LXe active
Top PMT Array, Liquid Level Meters, HV- FT
Liquid Level Meter-Yale
Bottom PMT Array, PTFE Vessel
Grids- Tiltmeters-Case
PMT Base (LLNL)
T. Shutt, SNOLAB, 8/22/6 14
Summary: XENON10 Backgrounds
Monte Carlo studies of Radioactivity (Background Events) from:
• Gamma / ElectronGammas inside Pb Shield• PMT (K/U/Th/Co)• Vessel: Stainless Steel (Co)• Contributions from Other Components
Xe Intrinsic Backgrounds (incl. 85Kr)External Gammas - Pb ShieldRn exclusionDetector Performance/Design• Gamma Discrimination Requirements• Use of xyz cuts instead of LXe Outer Veto
• Neutron BackgroundsInternal Sources: PMT (,n)External: Rock (,n): Muons in ShieldPunch-through neutrons: Generated by muons in rock
• NOTE: Active Muon Shield Not Required for XENON10 @ LNGSNeutron flux from muon interaction in Pb shield << Target Level
[Background Modeling U. FLORIDA / BROWN/COLUMBIA]
T. Shutt, SNOLAB, 8/22/6 15
XENON10 Shield Construction - LNGS
3500 mm
4400 mm Clearance Box 450 mm
Clearance Box 450 mm
Clearance to Crane Hook (after moving crane upwards) 20 mm
2410 mm
200 mm
2630 mm
Red-Shield Dimension Blue-Ex-LUNA Box Dimension
Crane Hook
Brown Design / LNGS Engineering 40 Tonne Pb / 3.5 Tonne PolyLow-Activity (210Pb 30 Bq/kg) inner Pb & Normal Activity (210Pb 500 Bq/kg) Outer Pb
Construction Underway: Contractor COMASUD – Mid May Expect Completion of Installation
LNGS (Ex-LUNA) Box Dimensions are critical constraints for shield - expansion of shield to accommodate much larger detector difficult
Inner Space for XENON10 detector 900 x 900 x 1075(h) mm
T. Shutt, SNOLAB, 8/22/6 16
XENON10: Punch-Through Neutron Backgrounds• High Energy Neutrons from Muons in
Rock— Poly in shield is not efficient in
moderating High Energy Muon-Induced Neutrons
— Depth is “standard” way to reduce high energy neutron flux (LNGS effective depth is 3050 mwe)
— Brown Monte Carlos show that: — Goal WIMP 1.3 evts/10 kg/mth: LNGS
depth comfortably achieves goal— Goal WIMP 1.3 evts/100 kg/mth: HE
Neutrons evts ~1/6 rate of dark matter. Much reduced comfort margin. (Continue to study mitigation strategies)
DM Goal(Rates for Current XENON10 Shield
Design)
NR Signal Rate Xe
@ 16 keVr
Soudan2.0 kmwe
Gran Sasso3.0 kmwe
Home-stake
4.3 kmwe
High Energy Neutron Relative Flux (from muons)
x6.5 x1 x1/5
1.3 evts/10kg/mthσ ~ 2x10-44 cm2
300 µdru
x1/10 x1/60 x1/300
1.3 evts/100kg/mthσ ~ 2x10-45 cm2
30 µdru
x1.1 x1/6 x1/30
1.3 evts/1000kg/mthσ ~ 2x10-46 cm2
3 µdru
x11 x2 x1/3
Ratio HE Neutron BG / WIMP Signal
For 2x10-46 cm2 also evaluating water/active shielding wrt all types of background
Additional margin could be achieved using anti-coincidence signal from muon veto (none currently in place for XENON10) around shield (c.f. CDMSII simulations indicate factor 15 reduction may be possible by tagging pions also generated in muon showers that generate HE neutrons). However, it will be important to verify that such a strategy works before relying on it. (CDMSII: Reisetter, U. Minn. / R Hennings-Yeomans, CWRU)
Mei and Hime, astro-ph/0512125, calculate HE neutron/dm ~1/2–1/3 for Ge detectors at Gran Sasso Depth
T. Shutt, SNOLAB, 8/22/6 17
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)
• Chromatographic separation on charcoal column
10 Kg-charocoal column system at Case
25 Kg purifed to < 10 ppt
KrXe
Cycle: > 1000 separation
feed
purg
e
reco
very
200 g/cycle, 2 kg/day
T. Shutt, SNOLAB, 8/22/6 18
XENON10 expected background• Dominant background: Stainless Steel Cryostat & PMTs
— Stainless Steel :100 mBq/kg 60Co • ~ 4x higher than originally assumed, but faster assembly
— PMTs - 89 x 1x1” sq Hamamatsu 8520• 17.2/<3.5/12.7/<3.9 mBq/kg, U/Th/K/Co• Increased Bg from high number of PMTs / trade off with increased position info. = Bg
diagnostic
• Expected background: ~ 0.4 cnts/kg/keV/day (before discr.)
€
Pn (L) ≅1
n!
L
λ
⎛
⎝ ⎜
⎞
⎠ ⎟n
e−
L
λ
• Analytical estimate— Single, low-energy Compton
scattering— Very forward peaked.— Probability of n scatters while
traversing distance L:
Electron recoil background 5-25 keVee
Radius (cm)
Dep
th (
cm)
OriginalXENON10 Goal<0.14 /keVee/kg/day
Current estimate: 2-3 x original goal
(Brown)
T. Shutt, SNOLAB, 8/22/6 19
Occupancy
Borexino
OPERA
HALL CHALL B
HALL A
LVD
CRESST2
CUORE
CUORICINO
LUNA2
DAMA
HDMSGENIUS-TF
MI R&D
XENON
COBRA
ICARUS
GERDA
WARP
XENON10: Underground at LNGS
T. Shutt, SNOLAB, 8/22/6 20
XENON Box: March 7 2006XENON Box: March 10, 2006
T. Shutt, SNOLAB, 8/22/6 21
Test Mounting Of Detector (June 22)
T. Shutt, SNOLAB, 8/22/6 22
XENON10 Example Low Energy Event
• Low Energy Compton Scattering EventS1=15.4 phe ~ 6 keVeeDrift Time ~38 μs = 76 mm(Max depth 150 mm)
• Bulk gamma calib shows avg S12.3 phe/keVee0.9 phe/keVr
• Trigger n>=4 in 80 ns window— Able to trigger on S1 for 10
keVr with >90% eff— Also catching S2 triggers
(with pretrigger look-back)
• Noise on separate PMT chans <<0.1 phe equiv
T. Shutt, SNOLAB, 8/22/6 23
Status of XENON10
SUSY TheoryModels
Dark Matter Data Plotterhttp://dmtools.brown.edu
CDMS II goal
SUSY TheoryModels
• 15 kg detector (~8 kg fiducial) now operational in Gran Sasso
• First low background operations in shield started 8/12.
• Calibrations ongoing— Activated Xe soon
• 164 + 236 keV lines• 80 keV beta.
— Neutron— External gammas
• Background close to expectation
• Results soon.
T. Shutt, SNOLAB, 8/22/6 24
Scaling LXe Detector: Fiducial BG Reduction /1• Compare LXe Detectors (factor 2 linear scale up each time)
15 kg (ø21 cm x 15 cm) -> 118 kg (ø42 cm x 30 cm) -> 1041 kg (ø84 cm x 60 cm)
— Monte Carlos simply assume external activity scales with area (from PMTs and cryostat) using XENON10 values from screening
>102 reduction
x10 reduction
15 kg 118 kg 1041 kgx2 linear x2 linearGross Mass
Fiducial Massdru = cts/keVee/kg/day
Low energy rate in FV before any ER vs NR rejection /keVee/kg/day
(Brown)
T. Shutt, SNOLAB, 8/22/6 25
Scaling LXe Detector: Fiducial BG Reduction /2
• Assuming ER are rejected at 99% for 50% acceptance of NR— Diagonal dashed lines show background x exposure giving 1 event leakage— If rej. 99% -> 99.5% and acc. 50% -> ~100% then all σ are better by 4x
>102 reduction
x10 reduction
15 kg 118 kg 1041 kgx2 linear x2 linearGross Mass
Fiducial Mass
XENON10 - 400 mdruee7 live-days x 8 kg fid
“118 kg” - 40 mdruee30 live-days x 20 kg fid
“1041 kg” - 0.2 mdruee1200 live-days x 100 kg fid
dru = cts/keVee/kg/day
1 week
1 month
1 year
4 years
1 leakage event (rej 99%)
σ = 4 10-43 cm2
σ = 4 10-44 cm2
σ = 2 10-46 cm2
Reference: Current CDMS II 90% CL σ = 2 10-43 cm2 for 100 GeV WIMP
Low energy rate in FV before any ER vs NR rejection /keVee/kg/day
(Brown)