Dark matter search with cryogenic
sodium iodide detectors
Felix Wagner
Institute of High Energy Physics, Austrian Academy of Sciences
20th Lomonosov Conference, 24th August 2021
August 24, 2021

Felix Wagner

Dark Matter Direct Detection
Relic dark matter particle scattering off detectormaterial nuclei.

galactic escape velocity
velocity distribution

Expected differential recoil rate:

Astro physics: Velocity distribution, escape velocity minimal velocity toDM-nucleon cross section~ A2 , ~ form factor

produce a recoil above ERParticle physics: Form factor, energy threshold,detector material, dark matter mass

August 24, 2021

Felix Wagner2

Dark Matter Direct Detection
Movement of the earth w.r.t. the sun
introduces an annual modulation in the
expected signal:

B(t) … Background
S0 … Constant signal share
Sm … Modulating signal share (~ 0.05 S0)*
*J. Billard et al. (2021), arXiv:2104.07634, p. 21
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Felix Wagner

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The DAMA/LIBRA results
Observation of positive evidence forthe presence of dark matterparticles via annual modulation.

Location

LNGS

Material

250 kg NaI(Tl)

Signal(s)Light (PMTs)

Particle Discrimination
Energy Threshold

Target: 250 kg sodium iodide
NaI(Tl) crystals.

Data taking

R. Bernabei et al. (2018), DOI:
10.15407/jnpae2018.04.307

August 24, 2021

Felix Wagner

no1keVee
since 1996

The DAMA/LIBRA results

R. Bernabei et al. (2018), DOI:
10.15407/jnpae2018.04.307

Modulation Amplitude: Sm= (0.0103±0.0008) /( keV×kg×day)
Exposure: 2.46 t×year over 20 annual cycles in 2-6 keV
C.L.: 12.9 σAugust 24, 2021

Felix Wagner5* based on standard scenario assumptions.

Dark Matter Landscape
Other experiments with NaI targets:Anais.

J. Amare et al., Phys. Rev. D 103, 102005 (2021)

Sabre.

M. Antonello et al., Eur. Phys. J. C (2019) 79: 363

Cosine.

G. Adhikari et al., Phys. Rev. Lett. 123,031302 (2019)… all of them measure scintillation light,
but no total energy deposition.

J. Billard et al. (2021), arXiv:2104.07634, p. 27
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Felix Wagner

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The COSINUS Experiment●

Two channel approach (heat, light):
In-situ measurement of nuclearenergy scale.

●NaI as target material: Immune
against material dependence.

●Operation as cryogenic detector: <1
keV nuclear recoil energy threshold.

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Felix Wagner

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Cryogenic Calorimeters
Small scintillating crystals (~50 g), operated
at cryogenic temperatures (~10-20 mK).
A particle recoil in the crystal produces heatand scintillation light.
Amount of emitted light depends on particle
type: Light quenching.
Sensitive thermometers (TES - transitionedge sensors) measure the temperature ofthe detector crystal.
August 24, 2021

Felix Wagner8Original detector conceptdeveloped by the CRESST
collaboration!

Cryogenic Calorimeters
Small scintillating crystals (~50 g), operated
at cryogenic temperatures (~10-20 mK).
A particle recoil in the crystal produces heatand scintillation light.
Amount of emitted light depends on particle
type: Light quenching.
Sensitive thermometers (TES - transitionedge sensors) measure the temperature ofthe detector crystal.
August 24, 2021

Felix Wagner

9Cryogenic Calorimeters

Light Yield: Light Energy / Phonon Energy

Small scintillating crystals (~50 g), operated
at cryogenic temperatures (~10-20 mK).
A particle recoil in the crystal produces heatand scintillation light.
Amount of emitted light depends on particle
type: Light quenching.
Sensitive thermometers (TES - transitionedge sensors) measure the temperature of
the detector crystal.
G. Angloher et al. (2016), DOI:
10.1140/epjc/s10052-016-4278-3
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Felix Wagner

10Superconducting Thermometers
A Transition Edge Sensor (TES)
measures the temperature of thedetector crystal.
A small increase in temperature
produces a large increase in resistance.
The changing electrical current is runthrough a coil, inducing a magnetic fieldchange.
The field is measured by a SQUID
amplifier, producing a voltage signal.
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Felix Wagner

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F. Pröbst et al., J. Low Temp. Phys. 100, 69 (1995)

Detector Response Model
Equivalent thermal circuit of the detector components
provides matrix-valued differential equation for all
temperatures:

Solution for thermometer temperature after particle recoilin the crystal:August 24, 2021

Felix Wagner

12Analysis Methods
Continuous data taking enables offline triggeringand various simulation methods.
Two independent software packages forvalidation:●●CAT (Cryogenic Analysis Tools):
ROOT/C++-based standard analysis.
Cait (Cryogenic Artificial Intelligence Tools):
Open Source Python Package for machinelearning-based raw data analysis.

August 24, 2021

Felix Wagner

F. Wagner (2021), DOI:
10.5281/zenodo.5091416

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Time Scale
COSINUS – 1π (2022-2025)
Exclude or confirm nuclear recoil
origin of DAMA, independent ofdark matter halo, for any interactionof dark matter with nuclei.
COSINUS – 2π (≥2026)
Investigate annual modulation
signature with COSINUS.

“It has been evaluated that if COSINUS excludes a DM scattering rate ofabout 0.01 events/( kg×day), with an energy threshold of 1.8keV, it will ruleout the explanations of DAMA/LIBRA in terms of DM scattering off sodium
and/or iodine.” - 2021 APPEC Committee Report
J. Billard et al. (2021), arXiv:2104.07634, p. 27
F. Kahlhöfer et al., JCAP 1805 (2018) no.05, 074

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Setup @ LNGS

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G. Angloher et al. (2021), arXiv:2106.07390

Setup @ LNGS
Construction @ LNGS (3600 mwe), starting 2021.
A PMT-equipped water tank acts as passive
shielding and active veto.
Result of simulation studies:
●
●
●

●

Cylindrical water tank, 7 m height anddiameter.
8 cm Cu.
No lead (Pb) layer: Water provides enoughshielding against gammas, lessmuon-induced events in Cu.
No polyethylen (PE) layer: Contaminations
could cause additional neutrons.

August 24, 2021

Felix Wagner16Baseline Design
Measurement at LNGS (2017).
66 g NaI crystal, 1.32 kg days exposure.
241

Am source (~60 keV).

Beaker-shaped light detector (Si).

NaI crystal

HP lightdetector

Three thermal components: Absorbercopper
crystal, thermometer and carrier crystal. housingTESinterface
F. Reindl et al., J. Phys. Conf. Ser. 1342 012099 (2020)
Schäffner, K. et al. J Low Temp Phys (2018)
August 24, 2021

Felix Wagner17Baseline Design
Measurement at LNGS (2017).
66 g NaI crystal, 1.32 kg days exposure.
241

Am source (~60 keV).

Beaker-shaped light detector (Si).

NaI crystal

HP lightdetector

Three thermal components: Absorbercopper
crystal, thermometer and carrier crystal. housing

TESinterface
F. Reindl et al., J. Phys. Conf. Ser. 1342 012099 (2020)
Schäffner, K. et al. J Low Temp Phys (2018)
August 24, 2021

Felix Wagner

18Challenges:● hygroscopicity● high Debye temperature● potassium (K) contamination

Baseline Design
Energy Threshold NaI:
8.26 +/- 0.02 keVEnergy Resolution NaI:
1.1 keV (baseline) - 4.5 keV (60 keV)
Energy Resolution Light:~0.6 keVee
Pulse shape identification of carrier
events.
August 24, 2021

F. Reindl et al., J. Phys. Conf. Ser. 1342 012099 (2020)
Schäffner, K. et al. J Low Temp Phys (2018)
Felix Wagner

19Current developments: Extended Pulse Shape Modelphonon part

Preliminary!

light part

Preliminary!

Based on F. Pröbst et al., J. Low Temp. Phys.
100, 69 (1995)
developed by V. Zema, paper in preparation
August 24, 2021

Felix Wagner

20Current developments: remoTES

remoTES idea first suggested by
M. Pyle et al. in 2015,
arXiv:1503.01200

NaI has to be exclusively handled incontrolled atmosphere:●●●●avoid the carrier crystal, thus avoid
that phonons have topass through another material
except of NaI
avoid the amorphous interface (e.g.
glue, grease, oil, …)
instead: profit from good e-phcoupling of Au

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Felix Wagner21

remoTES idea first suggested by
M. Pyle et al. in 2015,
arXiv:1503.01200

Current developments: remoTES
NaI has to be exclusively handled incontrolled atmosphere:●●●●

Results from above-ground test measurements

avoid the carrier crystal, thus avoid
that phonons have topass through another material
except of NaI
avoid the amorphous interface (e.g.
glue, grease, oil, …)
instead: profit from good e-phcoupling of Au

August 24, 2021

Felix Wagner

Absorbermaterial

Au-padSi

sputteredAu wireThreshold(eV)Preliminary!
Preliminary!
TeO2foil, glued

glued on pad

323

Preliminary!
2 wedge
bonds

1100

22

Current developments: remoTES
Measurement of first NaI remo-TES
detector is running this week in cryo2 of
CRESST at MPP.

Preliminary!

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Felix Wagner

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Todo List for Dark Matter Module👍 Operate NaI as cryogenic detector.
👍 Beaker-shaped light detector.
👍 Radiopure NaI crystals.

Prototype measurement results:
G. Angloher et al. JINST 12
P11007 (2017)
F. Reindl et al., J. Phys. Conf.
Ser. 1342 012099 (2020)
Schäffner, K. et al. J Low Temp
Phys (2018)

👍 Extended pulse shape model for NaI detector.
🚧 Phonon threshold of 1 keV (current: 8.23 keV).
August 24, 2021

Felix Wagner24Summary
Cosinus provides:●

Particle identification on event-by-event basis,●Low(er) threshold for nuclear recoils,●Precise energy information independent of event type,●Same sensitivity at smaller target mass (~1kg for COSINUS vs. 250kg forDAMA),… and brings therefore everything we need to validate the DAMA claim.

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The Collaborationwww.cosinus.it
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Backup

August 24, 2021

Felix Wagner

27Quenching Factor Uncertainty
Measurements of quenching factors atroom temperature disagree at low
energies.
This introduces an uncertainty on thenuclear recoil energy scale.

H. Joo et al., Astropart. Phys. 108 (2019), pp. 50–56

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Felix Wagner

28Perspective
Collection of a net exposure of 100kg days,
with 10 modules (50g) for 1 year (efficiency0.5), in a low-background cryogenic facility.
COSINUS – 1π (2022-2025)
Exclude or confirm nuclear recoil
origin of DAMA, independent ofdark matter halo, for any interactionof dark matter with nuclei.
COSINUS – 2π (≥2026)
Investigate annual modulation
signature with COSINUS.
August 24, 2021

“It has been evaluated that if COSINUS
excludes a DM scattering rate of about 0.01
events/( kg×day), with an energy thresholdof 1.8keV, it will rule out the explanations ofDAMA/LIBRA in terms of DM scattering off
sodium and/or iodine.” - 2021 APPEC
Committee Report
J. Billard et al. (2021), arXiv:2104.07634, p. 27
F. Kahlhöfer et al., JCAP 1805 (2018) no.05, 074

Felix Wagner

29Perspective

Dark matter exclusion limits for different
recoil energy thresholds, understandard scenario assumptions.

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Time Scale

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