T. Shutt, SNOLAB, 8/22/61 The XENON10 dark matter search T. Shutt Case Western Reserve University

T. Shutt, SNOLAB, 8/22/6 1

The XENON10 dark matter search

T. Shutt

Case Western Reserve University


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


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


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.


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


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


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


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


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.


“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


Neutron Elastic Recoil


80 keV Inelastic (131Xe)

110 keV inelastic

(19F)+ NR

5 mm radial cut reduces gamma events in nuclear recoils region.


LXe Active

PMTs (top 48)

Pulse tube cryocooler

PMTs (bottom 41)

Gas Region

XENON10: Cryostat Assembly

Vacuum Cryostat

Re-condenser


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)


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]


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


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


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


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)


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


XENON Box: March 7 2006XENON Box: March 10, 2006


Test Mounting Of Detector (June 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


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.


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)


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)

Documents

T. Shutt, SNOLAB, 8/22/61 The XENON10 dark matter search T. Shutt Case Western Reserve University