Latest results of CRESST- III’s search for sub-GeV/c² 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 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 September 10, 2019 2
Latest results of CRESST- III’s search for sub-GeV/c² dark matter CRESST basics September 10, 2019 3
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Expected spectrum of DM induced elastic, nuclear recoils: 𝑤 𝑓𝑡𝑑 𝑒𝑆 𝜍 0 𝑤 𝑤 𝑒𝜏 𝐹, 𝑤 𝑒 3 Ԧ 𝑒𝐹 ∝ න 𝑤 𝑔 Ԧ 𝑛 𝐸𝑁 𝑒𝐹 𝑤 𝑛𝑗𝑜 (𝐹) 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) September 10, 2019 4
Latest results of CRESST- III’s search for sub-GeV/c² dark matter The CRESST collaboration September 10, 2019 5
Latest results of CRESST- III’s search for sub-GeV/c² dark matter The CRESST experiment • Target: CaWO 4 @ O(10mK) • Signature: recoiling nucleus induced by scattering off dark matter particle • @ LNGS DM September 10, 2019 6
Latest results of CRESST- III’s search for sub-GeV/c² dark matter The CRESST experiment • Target: CaWO 4 • Signature: recoiling nucleus • Phonon signal: measurement of recoil energy Δ E/C = Δ T 1keV ~ 1µK September 10, 2019 7
Latest results of CRESST- III’s search for sub-GeV/c² dark matter The CRESST experiment • Target: CaWO 4 • Signature: recoiling nucleus • Phonon signal: energy • Read-out by a TES (transition edge sensor) September 10, 2019 8
Latest results of CRESST- III’s search for sub-GeV/c² dark matter The CRESST experiment • Target: CaWO 4 • Signature: recoiling nucleus • Phonon signal: energy • Read-out by a TES • Scintillation light signal: separated detector placed inside a reflective & scintillating housing, particle dependent September 10, 2019 9
Latest results of CRESST- III’s search for sub-GeV/c² dark matter The CRESST experiment • Target: CaWO 4 • Signature: recoiling nucleus • Phonon signal: energy • Read-out by a TES • Scintillation light signal: particle dependent Particle identification September 10, 2019 10
Latest results of CRESST- III’s search for sub-GeV/c² dark matter The CRESST experiment Normalized to 1 e - / γ Light yield=light signal/phonon signal by calibration α O Quenched light Ca for nuclear recoils W Energy / keV September 10, 2019 11
Latest results of CRESST- III’s search for sub-GeV/c² dark matter The CRESST experiment e - / γ Light yield=light signal/phonon signal Discrimination between • electron recoils, i.e. dominant radioactive background • nuclear recoils, i.e. potential DM signal α O Ca W Energy / keV September 10, 2019 12
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Searching for low-mass DM with CRESST-III September 10, 2019 13
Latest results of CRESST- III’s search for sub-GeV/c² dark matter SI results of CRESST-II phase 2 [Eur.Phys.J. C76(2016)25] September 10, 2019 14
Latest results of CRESST- III’s search for sub-GeV/c² dark matter SI results of CRESST-II phase 2 CRESST-II phase 2 (2014), Eur.Phys.J. C74 (2015)3184 [Eur.Phys.J. C76(2016)25] aka ‚TUM40‘ • TUM40: successfully reduced intrinsic background via in-house grown crystals Light yield Energy / keV September 10, 2019 15
Latest results of CRESST- III’s search for sub-GeV/c² dark matter SI results of CRESST-II phase 2 [Eur.Phys.J. C76(2016)25] • TUM40: successfully [arXiv:1908.06755] reduced intrinsic background • Modelling of em. background with Geant4 [arXiv:1908.06755] Light yield Energy / keV Poster V. Mokina September 10, 2019 16
Latest results of CRESST- III’s search for sub-GeV/c² dark matter SI results of CRESST-II phase 2 CRESST-II phase 2 (2015), Eur.Phys.J. C76 (2016)25 [Eur.Phys.J. C76(2016)25] aka ‚ Lise ‘ • TUM40: successfully reduced intrinsic background • Lise: low threshold 307eV open up sub-GeV/c²regime September 10, 2019 17
Latest results of CRESST- III’s search for sub-GeV/c² dark matter SI results of CRESST-II phase 2 [Eur.Phys.J. C76(2016)25] • TUM40: successfully reduced intrinsic lower threshold background • Lise: low threshold 307eV • combine both in CRESST-III September 10, 2019 18
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Optimized detector design reflective and scintillating housing block-shaped target crystal (with TES) light detector (with TES) instrumented CaWO 4 sticks (with holding clamps and TES) Detector design optimized for low-mass dark matter : cuboid crystal with strongly reduced dimension : 20 × 20 × 10 mm 3 and ≈ 24g • • goal: detection threshold of 𝟐𝟏𝟏 𝐟𝐖 self-grown crystal with low total background of ≈ 3 keV −1 kg −1 d −1 in 1,40 keV • • veto against surface related background : fully scintillating housing + instrumented sticks (“ iSticks ”) September 10, 2019 19
Latest results of CRESST- III’s search for sub-GeV/c² dark matter DAQ • New DAQ in CRESST-III: dead-time free, continuous sampling of pulse traces (25kS/s, 50TB/year) September 10, 2019 20
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Filtering • New DAQ in CRESST-III: dead-time free, continuous sampling Pulse template • Maximize signal-to-noise ratio in frequency space via optimum filter: use Gatti-Manfredi-filter for • triggering Baseline • and pulse height evaluation precise threshold value in energy units Before filtering After filtering September 10, 2019 21
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Threshold • 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 Amplitude distribution of a typical empty base line pulse trace (Detector specific) 30.1 eV September 10, 2019 22
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Efficiency determination Empty baseline Pulse Artificial = from recorded template pulse + data stream All triggered events Efficiency ≳ 60% over several decades Feed in analysis Passing selection criterions chain, incl. triggers and cuts September 10, 2019 23
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 September 10, 2019 24
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Detector A: neutron calibration • Quenching factors from neutron beam measurements e - / g • Unbinned maximum likelihood fit O W September 10, 2019 25
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Detector A: physics data e - / g 179 Ta + e - 179 Hf + n e (T 1/2 =1.8yr) e - / g L-shell M-shell O 11.3 keV 2.6 keV W O W September 10, 2019 26
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Detector A: physics data e - / g 441 events accepted 50% O recoils below 99.5% W recoils above O W 30.1eV 16keV September 10, 2019 27
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Detector A: physics data e - / g 411 events accepted 50% O recoils below Currently ongoing: run for detector tests and development; active magnetic 99.5% W recoils above field compensation O W 30.1eV 16keV September 10, 2019 28
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Detector A: physics data e - / g 411 events accepted 50% O recoils below Currently ongoing: run for detector tests and development; active magnetic 99.5% W recoils above field compensation O W 30.1eV 16keV Assume all accepted events are dark-matter caused Use Yellin‘s optimum interval method to set an exclusion limit September 10, 2019 29
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Detector A: exclusion limit SI [arXiv:1904.00498] September 10, 2019 30
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Detector A: exclusion limit SI [arXiv:1904.00498] Factor 10 improvement at 500 MeV/c² September 10, 2019 31
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Detector A: exclusion limit SI [arXiv:1904.00498] Experimental range extended down to 160 MeV/c² September 10, 2019 32
Latest results of CRESST- III’s search for sub-GeV/c² dark matter Detector A: exclusion limit SI [arXiv:1904.00498] Unexpected rise of event rate <200eV September 10, 2019 33
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