The MiniCLEANDark Matter Experiment

Stanley SeibertLos Alamos National Laboratory

August 3, 2010

Scintillation in Noble Liquids

Energy deposition in noble liquids produces short lived excited diatomic molecules in singlet and triplet states.

Pulse Shape Analysis

Electronic recoil

Nuclear Recoil

Triplet state highly suppressed!

Singlet Triplet

He ~10ns 13 s

Ne <18.2 ns 14.9 μs

Ar 7 ns 1.60 μs

Xe 4.3 ns 22 ns

Rejecting Electron-like Events

Discriminate with ratio of prompt to total light

Reject beta and gamma backgrounds with greater

than 108 efficiency

Single Phase Ar/Ne DetectorsAdvantages:

• Target material is relatively inexpensive(and swappable in MiniCLEAN)

• No need for electric fields to drift charge.

• Simpler detector design

• Able to use a spherical geometry

• Does not require 39Ar-depleted argon for large detectors

• Neon is clean enough to use for pp solar neutrinosDisadvantages:

• Lower A2 reduces coherent scattering enhancement

• Self-shielding from external backgrounds worse than other materials

• Atmospheric argon contains 39Ar, a high rate beta decay isotope (1 Bq/kg)

The DEAP and CLEAN Family of Detectors

DEAP-0:Initial R&D detector

DEAP-1:7 kg LAr2 warm PMTsAt SNOLab 2008

picoCLEAN:Initial R&D detector

microCLEAN:4 kg LAr or LNe2 cold PMTssurface tests at Yale

MiniCLEAN:500 kg LAr or LNe (150 kg fiducial mass)92 cold PMTsAt SNOLAB mid-2011DEAP-3600:

3600 kg LAr (1000 kg fiducial mass)266 warm PMTsAt SNOLAB 2012

50-tonne LNe/LAr Detector:pp-solar ν, supernova ν, dark matter <10-46 cm2

At DUSEL ~2016?

10-44 cm2

10-45 cm2

10-46 cm2

WIMP σ Sensitivity

MiniCLEAN Goals• Demonstrate the technical features of a 4π single-

phase detector using both liquid argon and neon.

• Characterize detector response to produce signal and background distributions using combination of calibration and Monte Carlo. Leverage this knowledge in our analysis.

• Perform a WIMP dark matter search competitive and complementary to next generation experiments with O(100 kg) fiducial mass.

• Develop the experience and verified simulation tools to design a 50 ton CLEAN experiment.

Simplified View

Liquid Ar/NeTarget

Liquid Ar/NeShielding

Acrylic

UV fluor(TPB)

PMTs

A Less Simple View

Courtesy J. Griego

Inner Vessel

PMT

OuterVessel

LAr/LNe

92 PMTs

TPB @ R=43 cm

PMTs @ R=81 cm

Optical Cassettes

PMT

AcrylicPlate

LightGuide

Top Hat

Courtesy J. Griego

R5912-02-MOD:14 dynodes

Pt photocathode underlayer

Water Shielding

Courtesy J. Griego

InnerVessel

OuterVessel

WaterShieldTank

Deck

Veto PMTs

SNOLAB

SurfaceFacility

2 km of rock(6000 mwe)

UndergroundLaboratory

Sudbury, Ontario, Canada

SNOLAB Facility

Personnel facilities

SNO Cavern

Ladder Labs

Cube Hall

Cryopit

Utility Area

South Drift

Phase III Stub

Utility Drift

Courtesy F. Lopez

Construction Progress: Outer Vessel

Construction Progress: Inner Vessel

Courtesy F. Lopez

Courtesy F. Duncan

Construction Progress: Cube Hall

Insert MiniCLEAN

here

MiniCLEAN WIMP AnalysisPerform a blind analysis with signal box in three reconstructed observables:

Ener

gy

Radius

Fpro

mpt

Use calibration data, simulation, and systematic uncertainties to optimize the final box.

Reconstructed Energy (keV)15 20 25 30 35

Eve

nts

per k

eV

0

50

100

150

200

250

300

350

400

Energy• A spherical 4π detector has very uniform energy response.

• We obtain the “electron equivalent” kinetic energy (keVee), as nuclear recoils have ~25% quenching factor.

• Nominal energy region of interest is 20-50 keVee.

Resolution @ 20 keVee = 15%

Radius: Position Reconstruction• No photon in MiniCLEAN can travel from event vertex to

a PMT!• We have developed a hybrid analytic/Monte Carlo based

maximum likelihood position reconstruction called ShellFit.• Includes all major optical effects.

Argon/Neon

PMTAcrylic/More TPB Surfaces

TPB

Light Yield UV table Visible TableN-pe Charge

Distrib

3(True radius/439 mm)0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Ave

rage

bia

s [fi

t - tr

ue ra

dius

] (m

m)

-25

-20

-15

-10

-5

0

5

10

15Single PE

ShellFit: Radial Bias

20 keV electrons

3(True radius/439 mm)0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Ave

rage

X re

solu

tion

(mm

)

0

20

40

60

80

100Single PE

ShellFit: Resolution (Cartesian)

20 keV electrons

Fprompt• Designed to be the simplest possible pulse shape

discriminant.• Fprompt = Charge in prompt window (150 ns) divided by

total charge. Ranges from 0 to 1.

Number of photoelectrons0 50 100 150 200 250 300 350 400 450 500

prom

ptF

00.10.20.30.40.50.60.70.80.9

1

)ee (keVeffT0 20 40 60 80 100 120 140 160

FIG. 7: Fprompt versus energy distribution for neutrons and! rays from an Am-Be calibration source. The upper bandis from neutron-induced nuclear recoils in argon, the lower-band is from background !-ray interactions.

promptF0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Even

ts/0

.01

wid

e bi

n

1

10

210

310

410

510

610-ray events! 7 10"1.7

100 nuclear recoil events

FIG. 8: Fprompt distribution for 16.7 million tagged !-rayevents from the 22Na calibration, and nuclear recoil eventsfrom the Am-Be calibration, between 120 and 240 photoelec-trons (approximately 43–86 keVee). No !-ray events are seenin the nuclear recoil region.

measured the triplet lifetime in DEAP-1 over the courseof the run to check that impurities did not build up inthe detector over time.

We use 22Na calibration data to measure the tripletlifetime. For each calibration run, we find all events thatpass the data cleaning cuts and contain over 200 photo-electrons. The raw traces for these events are aligned ac-cording to the measured trigger positions and summed.We then fit the following model to the average trace be-tween 500 and 3000 ns from the trigger:

f(t) = A exp(!t/!3) + B, (3)

where A is a normalization factor, !3 is the triplet life-time and B is a constant baseline term.

As a consistency check, we measured !3 for photo-electron bins of size 200 between 200 and 1600 photo-

(cm)fitZ-50 -40 -30 -20 -10 0 10 20 30 40 50

bin

(Hz)

fitR

ate

per Z

-510

-410

-310

-210

-110

1 Surface backgroundSNOLAB backgroundPSD signal

FIG. 9: Comparison of Zfit distribution for !-rays from thePSD data, and for high-Fprompt backgrounds during the run(labeled Surface backgrounds). Also shown, for reference, isthe distribution of high-Fprompt background events with thedetector operating underground at SNOLAB.

Days since Aug. 19, 20070 10 20 30 40 50 60

bg.

rate

(mH

z)pr

ompt

Hig

h F

0

2

4

6

8

FIG. 10: High-Fprompt background event rate versus time.The average background rate is 4.6 ± 0.2 mHz.

electrons and did not observe any systematic e!ect fromthe signal size. There are systematic errors associatedwith both the fit window and the linear baseline correc-tion discussed in Section III C. We estimated the size ofthe error associated with the fit window to be 40 ns bychanging the start and end times of the fit by 500 ns.We performed the fit for both corrected and uncorrectedtraces and estimated the size of the error associated withthe baseline to be 50 ns. We added the two estimatedsystematic errors to determine a combined systematicerror of 60 ns.

The measured lifetimes over the course of the runfor traces without the baseline correction are shown inFig. 12, in which the error bars shown are statistical only.We observe no significant increase in the impurity levelthroughout the run, and we measure the long time con-stant to be 1.46±0.06 (sys) µs, consistent with previousmeasurements [5, 13, 14]. Further analysis of systematic

6

M.G. Boulay et al. arXiv:0904.2930

Fprompt• Designed to be the simplest possible pulse shape

discriminant.• Fprompt = Charge in prompt window (150 ns) divided by

total charge. Ranges from 0 to 1.

M.G. Boulay et al. arXiv:0904.2930

BackgroundsMajor:

• 39Ar: 1 Bq per kg of atmospheric argon

• PMT Neutrons

• Rn daughters on surfaces

Sub-dominant:

• External gammas from steel and rock

• External neutrons from rock and cosmic ray spallation

Mitigating Backgrounds

• 39Ar: Cut with Fprompt

• PMT Neutrons: Low activity glass, pull PMTs back from fiducial volume, acrylic shielding, position reconstruction, timing distribution

• Rn daughters on surfaces: Modular design to assemble cassettes in gloveboxes, position reconstruction

• External gammas from steel and rock: Low activity steel, water shield, cut with Fprompt

• External neutrons from rock and cosmic ray spallation: Water shield, active cosmic ray veto.

Controlling Radon

15

•! Radon exposure limits can be placed to achieve a desired surface

activity. 1 m-2 day-1 is the MiniCLEAN spec, equal to the surface activity

achieved in the SNO neutral current detectors.

–! i.e. Exposure limits for class 3000 clean room at 25 C and 20% RH

Radon Daughter Deposition

27 July 2010 D. McKinsey, MiniCLEAN Review

• Goal of 1 decay per m2 per day on the TPB surface.

• Creating a model of Rn deposition to understand how to achieve this goal during assembly.

Neutron Cross-Sections• Modeling of neutrons is important for detector design and

optimizaton

• Carefully studying GEANT4 neutron simulations in argon/neon and making new measurements.

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!"#$%&'()*+,-&&*.#)'(-"&

/-'%$*!"#$%&'()*+,-&&*.#)'(-"*(&*,#0,-12)#1 32'*4%$2#&*%,#*567*$-8#,*'9%"*:;<=>3?@!!

=#8#,*("1#0#"1#"'*#A)('#1*&'%'#&*("*BC;<DE*F(&&("G*H*%$09%*I"%$*&'%'#*89()9*9%&*%*'9,#&99-$1*-J*C*K#@E*L2'*(&*%"*-,1#,*-J*F%G"('21#*&F%$$#,*("*),-&&*&#)'(-"

!"#$%&'"() !"#$%&'"()

K.J. Palladino

Sean MacMullin APS February 14, 2010

Conclusions•Optical model has been shown to work very well for medium mass and heavy nuclei (Hodgson, Nuclear Reactions and Nuclear Structure)•Depends strongly on (N-Z)/A•Na-22 approximates Ne-20 for now

Energy (MeV)0 5 10 15 20 25 30 35 40

Bar

ns

0

0.5

1

1.5

2

2.5

3

3.5

4

Na-22(n,EL)Ne-20(n,EL)

Geant4 simulation of total elastic cross-sections for 20Ne and 22Na

[degrees]C.M.

0 20 40 60 80 100 120 140 160 180

[mb/

sr]

/dd

1

10

210

310Na-22 Data (NNDC)

Ne-20 Data

S. MacMullin, et. al.

CalibrationDeveloping a calibration plan to understand detector response and model it in our Monte Carlo

Sources:

• 39Ar (natural and spike)

• 57Co

• 22Na

• AmBe

• 83Krm

• d-d neutron generator

• Light injection (visible and UV)

WIMP Sensitivity

WIMP Mass [GeV/c2]

Cro

ss-s

ecti

on [

cm

2]

(norm

ali

sed

to

nucle

on)

101

102

103

10-47

10-46

10-45

10-44

10-43

10-42

MiniCLEAN

CLEAN, natural Ar

CLEAN, depleted Ar

LUX

CDMS (2008)XENON10 (2007)

CLEAN, Ne

!"#$%&'(')*'+,'('-.'

!"#$%&'(')**'+,'('-.'

!"#$%&'(')***'+,'('-.'

Schedule

• September 2010: Underground infrastructure completed

• Winter 2010: Outer vessel in shield tank on stand

• May 2011: Inner vessel fabrication completed

• Summer 2011: Cassette assembly and installation into inner vessel

• Fall 2011: Detector commissioning and initial calibrations

• Winter 2011: Liquid argon dark matter run begins(projected lifetime: 2 years, followed by neon run)

Conclusion• Single phase noble liquid detectors offer a highly scalable

option for dark matter and neutrino detection.

• MiniCLEAN extends the DEAP/CLEAN series of detectors to 150 kg fiducial volume with liquid argon and neon.

• Broad R&D program studying Ne/Ar scintillation, cold PMTs, TPB properties, radon deposition, acrylic optics, and neutron cross-sections on argon and neon.

• Will perform a dark matter search and also demonstrate the techniques to be used in a future 50 ton detector.

• Construction is underway, with detector commissioning scheduled for fall 2011.

DEAP/CLEAN CollaboratorsUniversity of Alberta

B. Beltran, P. Gorel, A. Hallin, S. Liu, C. Ng, K.S. Olsen, J. Soukup

Boston UniversityD. Gastler, E. Kearns

Carleton UniversityM. Bowcock, K. Graham, P. Gravelle, C. Oullet

Harvard UniversityJ. Doyle

Los Alamos National LaboratoryK. Bingham, R. Bourque, V.M. Gehman, J. Griego, R. Hennings-Yeomans, A. Hime, F. Lopez, J. Oertel, K. Rielage, L. Rodriguez,

S. Seibert, D. Steele

Massachusetts Institute of TechnologyL. Feng, J.A. Formaggio, S. Jaditz, J. Kelsey, J. Monroe, K. Palladino

National Institute Standards and TechnologyK. Coakley

University of New MexicoM. Bodmer, F. Giuliani, M. Gold, D. Loomba, J. Matthews, P. Palni

University of North Carolina/TUNLM. Akashi-Ronquest, R. Henning

University of PennsylvaniaT. Caldwell, J.R. Klein, A. Mastbaum, G.D. Orebi Gann

Queen’s UniversityM. Boulay, B. Cai, M. Chen, S. Florian, R. Gagnon, V. Golovko,

P. Harvey, M. Kuzniak, J. Lidgard, A. McDonald, T. Noble, P. Pasuthip, C. Pollman, W. Rau, P. Skensved, T. Sonley, M. Ward

SNOLAB InstituteM. Batygov, F.A. Duncan, I. Lawson, O. Li, P. Liimatainen,

K. McFarlane, T. O’Malley, E. Vazquez-Jauregi

University of South DakotaV. Guiseppe, D.-M. Mei, G. Perumpilly, C. Zhang

Syracuse UniversityM.S. Kos, R.W. Schnee, B. Wang

TRIUMFP.-A. Amaudruz, A. Muir, F. Retiere

Yale UniversityW.H. Lippincott, D.N. McKinsey, J.A. Nikkel, Y. Shin