The SABRE Dark Matter Search Experiment · PDF fileThe SABRE Dark Matter Search Experiment...

The SABRE Dark Matter Search Experiment

Francis FroborgFor the SABRE Collaboration

DMUK18 January 2017

SABRE

SABRE

Motivation Concept Status & Outlook Conclusions

The DAMA/LIBRA Experiment

25 high purity NaI(Tl) crystalswith 9.7 kg each

2 PMTs per crystal coupled viaquartz light guide

Passive external shielding

Located at LNGS (∼ 3200 m.w.e.)

Modulation at 2– 6 keVee

Effect ∼ 2 %, 9.3σ C.L.

Peak end of May / beginning ofJune

2-6 keV

Time (day)

Res

idua

ls (c

pd/k

g/ke

V) DAMA/NaI 5 100 kg

(0.29 ton×yr)DAMA/LIBRA 5 250 kg

(0.87 ton×yr)

DAMA/LIBRA results and perspectives, Bled 2013

Francis Froborg SABRE 2 / 16


Not So Current Status - The Tension

XENON1T: Sensitivity

Guillaume Plante - XENON Dark Matter 2014 - UCLA - February 20, 2014 16 / 18

• Spin-independent WIMP-nucleon interaction cross section sensitivity of 2 ! 10!47 cm2

for WIMPs with a mass of 50 GeV/c2



What Makes SABRE Special?SABRE: Sodium iodide with Active Background REjection

HighpurityNaI(Tl)crystals

Improvebackgroundbyreducing40K,87Rb,and

others

Improvedperformance

Bettersensitivityinthelowenergyregion

Activeveto

Furtherreducebackground,especially40K

Twolocations

Powerfultestagainstenvironmentaleffects

SABRE

SABRE



Active Veto: The Principle

40K Decay

natK ' 93% 39K + 0.012% 40K + 7% 41K

3 keV Auger e− accompanying 1.46 MeV γ after electron capture⇒ Right in the region of interest

DAMA reports 13 ppb natK contamination in their crystals

40K

40Ar

1.46 MeV g40Ca

b- 89.3%Q = 1.3 MeV

EC 10.7%

0

2

4

6

8

10

2 4 6 8 10 Energy (keV)

Rat

e (c

pd/k

g/ke

V)



Active Veto: The Principle

40K Decay

natK ' 93% 39K + 0.012% 40K + 7% 41K

3 keV Auger e− accompanying 1.46 MeV γ after electron capture⇒ Right in the region of interest⇒ Coincidence between e− and γ can be used to veto such events

DAMA reports 13 ppb natK contamination in their crystals

40K

40Ar

1.46 MeV g40Ca

b- 89.3%Q = 1.3 MeV

EC 10.7%

PMTs

� photons

e-

Crystal Module



High Purity CrystalsThe NaI Powder

Development of Ultra High Purity Powder

Collaboration with 2 industrial partners for production

Independent high sensitivity impurity measurements

R&D on further purification ongoing

Sigma- DAMA DAMAElement Aldrich [ppb] Powder [ppb] Crystal [ppb]

K 3.5 (18)* 100 ∼13Rb 0.2 n.a. < 0.35U < 1.7 (< 10−3)** ∼ 0.02 0.5 –7.5×10−3

Th < 0.5 (< 10−3)** ∼ 0.02 0.7 –10×10−3

* Independent measurement** Preliminary measurement at PNNL; full validation needed.

Bernabei et al., NIM A592 (2008) 297-315



High Purity Crystal

First Larger Crystal

2-kg crystal made out of Astrogradepowder

88-mm diameter similar to final crystals

Good scintillation properties

〈Rb〉 < 0.1 ppb (DAMA < 0.35 ppb)

39K [ppb] Seastar PNNL DAMA

A 9± 1 10.0± 0.7B 7± 1 9.1± 0.3D 11± 1 9.7± 0.4E 9± 1 9.8± 0.4

Average 9 9.6 13



Improved Performance

Higher light yield, lower threshold

PMTs directly coupled to crystal

Pre-amplifier developed at LNGS to suppressafterglow coincidence rate

Improved PMTs

High quantum efficiency: ∼ 35 %

Low radioactivity: ∼ 1 mBq U, Th, Co; ∼ 10 mBq K

Further improvements in development

Development by Hamamatsu in collaboration withPrinceton



Two Locations: Northern and Southern Hemisphere

∼ 3000 m.w.e shielding at both locations

Twin detectors for optimum comparability

Both detectors will run in parallel

LNGS, Italy SUPL, Australia

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Background Expectations

Total Background Crystals

)eeEnergy (keV0 5 10 15 20 25 30

)ee

Rat

e (c

pd/k

g/ke

V

0.1

0.2

0.3

0.4

0.5

0.6

0.7VetoNo Veto

shielding power4Total expected SABRE backgrounds with 10

No Veto

Veto

Crystal background only

Energy (keV)0 1 2 3 4 5 6 7 8 9 10

)ee

Cou

nt R

ate

(cpd

/kg/

keV

0

0.05

0.1

0.15

0.2

0.25

Total with veto

Rb (upper limit)

K crystals others

other backgrounds



ExpectationsSensitivity

Sensitivity

3 years stable detector operations

No other seasonal effect in ROI(2-6 keVee)

50 kg NaI(Tl) array

0.15 cpd/kg/keV totalbackground in ROI

⇒ 6σ to refute modulation

⇒ 4σ to verify modulation



SABRE North: Proof of Principle

Proof-of-Principle: 5.5-kg ultra high-purity NaI(Tl) crystals

φ1.4× 1.5 m veto filled with pseudocumene + PPO

Additional water / lead / polyethylene shielding around the veto



Proof of Principle

Goals

Measure impurity levels of firsthigh-purity crystal(s)

Determine effectiveness of veto

Status

Many components available

Commissioning of vessel inPrinceton completed, delivered toLNGS

Preparations at LNGS in progress



Stawell Underground Physics Laboratory (SUPL)

First underground lab insouthern hemisphere

∼ 240 km west of Melbourne

Decline gold mine

Site 1.02 km deep (∼ 3 km.w.e.similar to LNGS)

Electricity & optical fibreavailable

Can be reached by truck/car

Clean room design similar toSNOLab

Construction started; expectedto finish in late 2017

P."Urquijo,"SABRE"&"SUPL,"Cosmo"2016

gradient fill acronym only

VIBRATION This concept is high tech, providing a combination of a focal point andconcentric rings. This style implies several relevant themes: the perspectiveof looking down a tunnel (into the earth from above); revolving computer spools;and a maze surrounding a central truth. The colourway is cool and suggests a laboratory, and the font is modern, clean and friendly.

STAWELL UNDERGROUND PHYSICS LABORATORY

OVERVIEW

COLOUR

VARIANTS

STAWELL

PHYSICS LABUNDERGROUND

SUPL

20

SUPL Detail SUPL"Floor"Plan

10

34.5 m

Future"expansion"allowed"in"design

10 m

CleanKroom,"low"radon"areas

Concept Progress Status Conclusions

Collaboration

SABRE

SABRE

Adelaide UniversityAustralian National UniversitySwinburne UniversityUniversity of Melbourne

LNGS & GSSIINFN RomeUniversity of Milano & INFN

Imperial College London

PNNLPrinceton University




Collaboration

SABRE

SABRE

Adelaide UniversityAustralian National UniversitySwinburne UniversityUniversity of Melbourne

LNGS & GSSIINFN RomeUniversity of Milano & INFN

Imperial College London

LLNLPNNLPrinceton University



Conclusions & Outlook

Conclusions

WIMP interpretation of DAMA modulation signal in tension with otherexperiments

Independent NaI(Tl) experiments needed⇒ SABRE

Ultra high purity NaI(Tl) in preparation⇒ first breakthrough!

Low background with high purity materials and active veto

High light yield & lower threshold due to improved, pre-amplifiedPMTs directly coupled to crystal

Outlook

First high-purity NaI(Tl) crystal grown

Proof of principle at LNGS in preparation

Full-scale twin detectors in preparation at LNGS (Italy) and SUPL(Australia)


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