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Latest results of CRESST- IIIs search for sub-GeV/c dark matter Holger Kluck on behalf of the CRESST collaboration 16th International Conference on September 10, 2019 Topics in Astroparticle and Underground Physics (TAUP2019) Latest

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

16th International Conference on Topics in Astroparticle and Underground Physics (TAUP2019) Holger Kluck

  • n behalf of the CRESST collaboration

September 10, 2019

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Outline

  • CRESST basics:

How the experiment works

  • Searching for low-mass DM with CRESST-III

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

CRESST basics

September 10, 2019 3

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

September 10, 2019

Expected spectrum of DM induced elastic, nuclear recoils:  Spectrum is steep for low mass DM  Search for light DM requires a low detection threshold  Interactions traditionally classified as spin-independent (SI) or spin-dependent (SD)

𝑒𝑆 𝑒𝐹 ∝ 𝜍0 𝑛𝐸𝑁 න

𝑤𝑛𝑗𝑜(𝐹) 𝑤𝑓𝑡𝑑

𝑒3 Ԧ 𝑤 𝑔 Ԧ 𝑤 𝑤 𝑒𝜏 𝐹, 𝑤 𝑒𝐹

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

The CRESST collaboration

September 10, 2019 5

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

The CRESST experiment

  • Target: CaWO4 @ O(10mK)
  • Signature: recoiling

nucleus induced by scattering off dark matter particle

  • @ LNGS

September 10, 2019

DM

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

The CRESST experiment

  • Target: CaWO4
  • Signature: recoiling

nucleus

  • Phonon signal:

measurement of recoil energy ΔE/C = ΔT 1keV ~ 1µK

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

The CRESST experiment

  • Target: CaWO4
  • Signature: recoiling

nucleus

  • Phonon signal: energy
  • Read-out by a TES

(transition edge sensor)

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

The CRESST experiment

  • Target: CaWO4
  • Signature: recoiling

nucleus

  • Phonon signal: energy
  • Read-out by a TES
  • Scintillation light signal:

separated detector placed inside a reflective & scintillating housing, particle dependent

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

The CRESST experiment

  • Target: CaWO4
  • Signature: recoiling

nucleus

  • Phonon signal: energy
  • Read-out by a TES
  • Scintillation light signal:

particle dependent  Particle identification

September 10, 2019 10

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

The CRESST experiment

September 10, 2019

Energy / keV Light yield=light signal/phonon signal e-/γ α O W Ca

Normalized to 1 by calibration Quenched light for nuclear recoils

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

The CRESST experiment

September 10, 2019

Energy / keV Light yield=light signal/phonon signal e-/γ α O W Ca Discrimination between

  • electron recoils,

i.e. dominant radioactive background

  • nuclear recoils,

i.e. potential DM signal

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Searching for low-mass DM with CRESST-III

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

SI results of CRESST-II phase 2

September 10, 2019

[Eur.Phys.J. C76(2016)25]

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

SI results of CRESST-II phase 2

September 10, 2019

Light yield Energy / keV

[Eur.Phys.J. C76(2016)25]

CRESST-II phase 2 (2014), Eur.Phys.J. C74 (2015)3184 aka ‚TUM40‘

  • TUM40: successfully

reduced intrinsic background via in-house grown crystals

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

SI results of CRESST-II phase 2

September 10, 2019

Light yield Energy / keV

[Eur.Phys.J. C76(2016)25]

  • TUM40:

successfully reduced intrinsic background

  • Modelling
  • f em. background

with Geant4 [arXiv:1908.06755]  Poster V. Mokina

[arXiv:1908.06755]

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

SI results of CRESST-II phase 2

September 10, 2019

  • TUM40:

successfully reduced intrinsic background

  • Lise: low

threshold 307eV  open up sub-GeV/c²regime

[Eur.Phys.J. C76(2016)25]

CRESST-II phase 2 (2015), Eur.Phys.J. C76 (2016)25 aka ‚Lise‘

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

SI results of CRESST-II phase 2

September 10, 2019

  • TUM40: successfully

reduced intrinsic background

  • Lise: low

threshold 307eV

  • combine both

in CRESST-III lower threshold

[Eur.Phys.J. C76(2016)25]

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Optimized detector design

September 10, 2019

Detector design optimized for low-mass dark matter:

  • cuboid crystal with strongly reduced dimension: 20 × 20 × 10 mm3 and ≈ 24g
  • goal: detection threshold of 𝟐𝟏𝟏 𝐟𝐖
  • self-grown crystal with low total background of ≈ 3 keV−1kg−1d−1 in 1,40 keV
  • veto against surface related background: fully scintillating housing +

instrumented sticks (“iSticks”) instrumented CaWO4 sticks (with holding clamps and TES) reflective and scintillating housing light detector (with TES) block-shaped target crystal (with TES)

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

DAQ

September 10, 2019

  • New DAQ in CRESST-III:

dead-time free, continuous sampling

  • f pulse traces (25kS/s, 50TB/year)

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Filtering

September 10, 2019

  • New DAQ in CRESST-III:

dead-time free, continuous sampling

  • Maximize signal-to-noise ratio in

frequency space via optimum filter:  use Gatti-Manfredi-filter for

  • triggering
  • and pulse height evaluation

 precise threshold value in energy units Pulse template Baseline Before filtering After filtering

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Threshold

September 10, 2019

Amplitude distribution of a typical empty base line pulse trace

  • New DAQ in CRESST-III:

dead-time free, continuous sampling

  • Maximize signal-to-noise ratio in

frequency space via optimum filter

  • Set threshold based on noise

distribution after optimum filter

30.1 eV

22 (Detector specific)

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Efficiency determination

September 10, 2019

+ =

Empty baseline from recorded data stream Pulse template Artificial pulse Feed in analysis chain, incl. triggers and cuts All triggered events Passing selection criterions  Efficiency ≳60%

  • ver several decades

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Status of CRESST-III phase 1

  • May 2016:

10 CRESST-III modules installed

  • Jul 2016 – Feb 2018:

data taking (80% blinded, 20% training set)

  • Detector A

 lowest nuclear recoil threshold so far: 30.1 eV

  • Target crystal mass: 23.6g
  • Gross exposure: 5.6 kg d
  • [arXiv:1904.00498],

accepted by Phys.Rev.D  this talk

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: neutron calibration

  • Quenching factors from

neutron beam measurements

  • Unbinned maximum

likelihood fit

September 10, 2019

e-/g W O

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: physics data

September 10, 2019

e-/g O W

179Ta + e-  179Hf + ne (T1/2=1.8yr)

M-shell 2.6 keV L-shell 11.3 keV

e-/g O W

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: physics data

September 10, 2019

e-/g O W 50% O recoils below 99.5% W recoils above 30.1eV 441 events accepted

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16keV

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: physics data

September 10, 2019

e-/g O W 50% O recoils below 99.5% W recoils above 411 events accepted

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 Currently ongoing: run for detector tests and development; active magnetic field compensation 30.1eV 16keV

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: physics data

September 10, 2019

e-/g O W 50% O recoils below 99.5% W recoils above 411 events accepted Assume all accepted events are dark-matter caused  Use Yellin‘s optimum interval method to set an exclusion limit

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 Currently ongoing: run for detector tests and development; active magnetic field compensation 30.1eV 16keV

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: exclusion limit SI

September 10, 2019

[arXiv:1904.00498]

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: exclusion limit SI

September 10, 2019

[arXiv:1904.00498]

Factor 10 improvement at 500 MeV/c²

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: exclusion limit SI

September 10, 2019

[arXiv:1904.00498]

Experimental range extended down to 160 MeV/c²

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: exclusion limit SI

September 10, 2019

[arXiv:1904.00498]

Unexpected rise of event rate <200eV

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: exclusion limit SD neutron

September 10, 2019

[arXiv:1904.00498]

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: exclusion limit SD neutron

September 10, 2019

Same data as before but analyzed with spin-dependent signal expectation “target”: 17O, natural abundance ~0.04%  4.6 ⋅ 10−4 kg days of 17O exposure

[arXiv:1904.00498]

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Detector A: exclusion limit SD neutron

September 10, 2019

Li2MoO4, Eur.Phys.J. C79 (2019)630 10h measurement above ground  7.91 ⋅ 10−5 kg days of 7Li exposure

[arXiv:1904.00498]

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Summary

  • First run of CRESST-III phase 1: Jul 2016 – Feb 2018

– Detector A: unprecedented low threshold of 30eV for nuclear recoils – x10 improvement @ 500 MeV/c² – Extend range down to 160 MeV/c² – Leading sensitivity from 160 MeV/c² to 1.8 GeV/c²

  • But that is not the end:

– Data taking to understand backgrounds with upgraded detectors – Ongoing modelling of background sources

New frontiers: new potentials & new challenges!

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

Backup

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

New Migdal Results

September 10, 2019

Spin-Independent (SI) Spin-Dependent (SD)

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Latest results of CRESST-III’s search for sub-GeV/c² dark matter

The CRESST experiment

September 10, 2019

n shield: 45cm PE + inner PE Active µ veto γ shield: 20cm Pb 14cm Cu against background from Pb Cryostat

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