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First results from the CRESST-III low-mass dark matter program

CRESST Collaboration, A. H. Abdelhameed, G. Angloher, P. Bauer, A. Bento, E. Bertoldo, C. Bucci, L. Canonica, A. D'Addabbo, X. Defay, S. Di Lorenzo, A. Erb, F. v. Feilitzsch, S. Fichtinger, N. Ferreiro Iachellini, A. Fuss, P. Gorla, D. Hauff, J. Jochum, A. Kinast, H. Kluck, H. Kraus, A. Langenkämper, M. Mancuso, V. Mokina, E. Mondragon, A. Münster, M. Olmi, T. Ortmann, C. Pagliarone, L. Pattavina, F. Petricca, W. Potzel, F. Pröbst, F. Reindl, J. Rothe, K. Schäffner, J. Schieck, V. Schipperges, D. Schmiedmayer, S. Schönert, C. Schwertner, M. Stahlberg, L. Stodolsky, C. Strandhagen, R. Strauss, C. Türkoglu, I. Usherov, M. Willers, V. Zema

TL;DR

This paper reports the inaugural results from the CRESST-III low-mass dark matter program, achieving a nuclear-recoil threshold of 30.1 eV in a ~24 g CaWO4 detector with phonon-light readout, enabling sensitivity to DM masses as low as 160 MeV/c^2. It introduces new data-processing techniques, including an offline optimum-filter trigger and a robust neutron-calibration framework to define light-yield bands and quenching factors, and presents a detailed efficiency and exposure analysis for a low-threshold search. The results yield the strongest limits to date for sub-GeV DM in CaWO4 and demonstrate significant gains over previous phases, while also reporting intriguing low-energy features and a 540 eV line that merit further hardware investigation. The work also provides first steps in spin-dependent searches using the 17O isotope, illustrating the broader scientific potential of the CRESST-III low-threshold approach.

Abstract

The CRESST experiment is a direct dark matter search which aims to measure interactions of potential dark matter particles in an earth-bound detector. With the current stage, CRESST-III, we focus on a low energy threshold for increased sensitivity towards light dark matter particles. In this manuscript we describe the analysis of one detector operated in the first run of CRESST-III (05/2016-02/2018) achieving a nuclear recoil threshold of 30.1eV. This result was obtained with a 23.6g CaWO$_4$ crystal operated as a cryogenic scintillating calorimeter in the CRESST setup at the Laboratori Nazionali del Gran Sasso (LNGS). Both the primary phonon/heat signal and the simultaneously emitted scintillation light, which is absorbed in a separate silicon-on-sapphire light absorber, are measured with highly sensitive transition edge sensors operated at ~15mK. The unique combination of these sensors with the light element oxygen present in our target yields sensitivity to dark matter particle masses as low as 160MeV/c$^2$.

First results from the CRESST-III low-mass dark matter program

TL;DR

This paper reports the inaugural results from the CRESST-III low-mass dark matter program, achieving a nuclear-recoil threshold of 30.1 eV in a ~24 g CaWO4 detector with phonon-light readout, enabling sensitivity to DM masses as low as 160 MeV/c^2. It introduces new data-processing techniques, including an offline optimum-filter trigger and a robust neutron-calibration framework to define light-yield bands and quenching factors, and presents a detailed efficiency and exposure analysis for a low-threshold search. The results yield the strongest limits to date for sub-GeV DM in CaWO4 and demonstrate significant gains over previous phases, while also reporting intriguing low-energy features and a 540 eV line that merit further hardware investigation. The work also provides first steps in spin-dependent searches using the 17O isotope, illustrating the broader scientific potential of the CRESST-III low-threshold approach.

Abstract

The CRESST experiment is a direct dark matter search which aims to measure interactions of potential dark matter particles in an earth-bound detector. With the current stage, CRESST-III, we focus on a low energy threshold for increased sensitivity towards light dark matter particles. In this manuscript we describe the analysis of one detector operated in the first run of CRESST-III (05/2016-02/2018) achieving a nuclear recoil threshold of 30.1eV. This result was obtained with a 23.6g CaWO crystal operated as a cryogenic scintillating calorimeter in the CRESST setup at the Laboratori Nazionali del Gran Sasso (LNGS). Both the primary phonon/heat signal and the simultaneously emitted scintillation light, which is absorbed in a separate silicon-on-sapphire light absorber, are measured with highly sensitive transition edge sensors operated at ~15mK. The unique combination of these sensors with the light element oxygen present in our target yields sensitivity to dark matter particle masses as low as 160MeV/c.

Paper Structure

This paper contains 19 sections, 2 equations, 9 figures.

Table of Contents

  1. Introduction
  2. CRESST-III Setup and Detector Design
  3. Experimental Setup
  4. CRESST-III Detector Design
  5. Dead-time free Recording and Offline Triggering
  6. Optimal Trigger Threshold
  7. Energy Calibration and Event Selection
  8. Energy Calibration
  9. Light Yield Description using Neutron Calibration Data
  10. Data Pre-Selection
  11. Event Selection
  12. Efficiency / Signal Survival Probability
  13. Light Yield
  14. Energy Spectrum
  15. Results
  16. ...and 4 more sections

Figures (9)

  • Figure 1: Schematic of a CRESST-III detector module (not to scale). Parts in blue are made from CaWO$_4$, the TESs are sketched in red. The block-shaped target (absorber) crystal has a mass of [$\sim$24]g, its dimensions are [(20x20x10)]mm$^{3}$. It is held by three instrumented CaWO$_4$ holding sticks (iSticks), two at the bottom and one on top. Three non-instrumented CaWO$_4$ holding sticks keep the square-shaped silicon-on-sapphire light detector in place. Its dimensions are [(20x20x0.4)]mm$^3$.
  • Figure 2: Number of expected noise triggers surviving event selection per []kg day as function of a chosen trigger threshold for detector A. The threshold chosen for this work is indicated by the dashed line at [30.1]eV.
  • Figure 3: Neutron calibration data for detector A in the light yield versus energy plane. We fit these data to determine the bands for $\beta$/$\gamma$-events (blue), nuclear recoils off oxygen (red) and tungsten (green), where the respective lines correspond to the upper and lower [90]% boundaries of the respective band. The band description follows strauss_energy-dependent_2014.
  • Figure 4: Efficiency obtained from simulated events and defined as probability for a valid signal event to be triggered (light gray) and pass the selection criteria (dark gray) as a function of injected (simulated) energy. The red line is a fit of the threshold with an error function, confirming the claimed value of [30.1]eV.
  • Figure 5: Light yield versus energy of events in the dark matter dataset, after selection criteria are applied (see section \ref{['subsec:eventselection']}). The blue band indicates the [90]% upper and lower boundaries of the $\beta$/$\gamma$-band, red and green the same for oxygen and tungsten, respectively. The yellow area denotes the acceptance region reaching from the mean of the oxygen band (red dashed line) down to the [99.5]% lower boundary of the tungsten band. Events in the acceptance region are highlighted in red. The position of the bands is extracted from the neutron calibration data as shown in figure \ref{['fig:neutroncalibration']}.
  • ...and 4 more figures