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Testing spin-dependent dark matter interactions with lithium aluminate targets in CRESST-III

G. Angloher et al. (CRESST Collaboration)
Phys. Rev. D 106, 092008 – Published 28 November 2022
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  • INTRODUCTION
  • DETECTOR DESIGN AND EXPERIMENTAL SETUP
  • DATA ANALYSIS
  • DARK MATTER RESULTS
  • CONCLUSION
  • ACKNOWLEDGMENTS
    • References

    Abstract

    In the past decades, numerous experiments have emerged to unveil the nature of dark matter, one of the most discussed open questions in modern particle physics. Among them, the Cryogenic Rare Event Search with Superconducting Thermometers (CRESST) experiment, located at the Laboratori Nazionali del Gran Sasso, operates scintillating crystals as cryogenic phonon detectors. In this work, we present first results from the operation of two detector modules which both have 10.46 g LiAlO2 targets in CRESST-III. The lithium contents in the crystal are Li6, with an odd number of protons and neutrons, and Li7, with an odd number of protons. By considering both isotopes of lithium and Al27, we set the currently strongest cross section upper limits on spin-dependent interaction of dark matter with protons and neutrons for the mass region between 0.25 and 1.5  GeV/c2.

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    • Received 25 July 2022
    • Accepted 15 November 2022

    DOI:https://doi.org/10.1103/PhysRevD.106.092008

    © 2022 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Particle dark matter
    1. Physical Systems
    Weakly interacting massive particles
    1. Techniques
    CryogenicsDark matter detectors
    Gravitation, Cosmology & Astrophysics

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    Vol. 106, Iss. 9 — 1 November 2022

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    Images

    • Figure 1
      Figure 1

      The Li1 detector module. Inside the copper housing, a LiAlO2 crystal (right, transparent) as a target for particle scattering is held by three copper sticks as a target for particle scattering. Next to the crystal a SOS light detector (left, gray) is mounted. The inside of the housing is covered with reflective foil, best visible on the detached side of the module (center, lower part of the picture).

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    • Figure 2
      Figure 2

      Overlay of the normalized Li1 light detector energy count distribution of the iron line from scintillation light (black, bottom x axis) and the iron line from direct hits (purple dotted, top x axis). The two x axes are shifted and scaled, such that the average value of the two iron lines overlap. Their ratio determines the collected light of the target (see text).

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    • Figure 3
      Figure 3

      Visualization of the surviving (purple) and cut (gray) events in the Li1 DM dataset. Left: the distribution of decay times in the phonon channel over pulse heights in the phonon channel. The band of recoil events is clearly visible and mostly distinct from the artefact events. For pulse heights below 0.2 V the band widens, which degrades the discriminating power of quality cuts. Right: the distribution of pulse heights in the light channel versus the corresponding pulse height in the phonon channel. Again, the band of particle recoils is clearly visible. For low phonon pulse heights the event class of foil events appears: due to their high pulse height in the light channel, higher than for regular target recoils, these events can be rejected as background. In both pictures the vertical event bands, as well as the secondary horizontal event bands, are SQUID resets caused by high energetic recoils.

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    • Figure 4
      Figure 4

      Recoil energy spectrum for the Li1 (gray) and Li2 (black) modules. Inset: the energy region up to 8 keV. The most prominent event clusters are the LEE and the two iron lines (purple dashed, K−α; purple dotted, K−β). Main figure: the energy region up to 0.5 keV, dominated by the LEE. The Li1’s LEE is less prominent due to the cut based on light channel information, which removes the foil events.

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    • Figure 5
      Figure 5

      The normalized trigger rate (gray) and survival rate (black) of simulated Li1 events (Li2 events in inset), as a function of the simulated recoil energy. The latter provides a realistic estimate of the survival probability. The energy threshold (olive, dashed) is the recoil energy at which the fitted error function (red) drops below 0.5 times the constant triggered fraction above threshold. The constant trigger efficiency for Li1 is (85.71±0.01)% and the trigger energy threshold (83.60±0.02)  eV. For Li2 the trigger efficiency is (81.26±0.08)% and the trigger energy threshold (94.09±0.13)  eV.

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    • Figure 6
      Figure 6

      Fitted light yield bands as a function of the recoil energy in the Li1 neutron (left) and blind (right) datasets, after application of the selection criteria discussed in Sec. 3c. Electron/γ (blue) and nuclear recoils off the nuclei with odd proton number (lithium red, aluminium green) cluster in bandlike structures and are fitted with Gauss distributions, with energy-dependent means and standard deviations. The acceptance region for DM candidates (light green) is chosen as the lower half of the lithium and aluminium bands, mitigating the EM background.

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    • Figure 7
      Figure 7

      Recoil energy spectrum of particle events inside the target of Li1. Left: the recoil spectrum up to 30 keV (black), the ROI for the DM search ends at 5.5 keV, indicated by the gray shade. The choice of the ROI is motivated in the text. The three prominent contributions are the clearly visible iron line (purple dashed, K−α; purple dotted, K−β), the tritium background (olive line to guide the eye), and the LEE. The events within the acceptance region are considered nuclear recoil candidates (red). Right: the region below 0.5 keV, which is dominated by the LEE. The recoil energy spectrum of all recoil candidate events (black dots) can be fitted with the sum of an exponential (gray, dotted) and a power law component (gray, dashed).

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    • Figure 8
      Figure 8

      The exclusion limits for proton-only (left) and neutron-only (right) spin-dependent DM-nucleus cross sections versus DM particle mass set by various experiments compared with the two lithium modules described in this work with Li6, Li7, and Al27. This work gives the most stringent limits between 0.25 and 2.5  GeV/c2 for proton only and between 0.16 and 1.5  GeV/c2 for neutron-only interactions. The solid red line shows the Li1 limits which includes the scintillation light information and the dashed red line shows the Li2 limits where no light information was available (hence worse). The previous aboveground results from CRESST using the same detector material and procedure with higher threshold and lower exposure are also shown with the solid black line [7]. Also, CRESST-III 2019 results for neutron-only interactions using O17 are shown also with the dashed light-blue line (right) [4]. Additionally, we show the limits from other experiments: EDELWEISS [38] and CDMSlite with Ge73 [39], PICO with F19 [40], LUX [41] which use Xe129+Xe131, J. I. Collar with H1 [42], and the constraint derived in [43] from Borexino.

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