Constraints on the Interactions between Dark Matter and Baryons from the X-ray Quantum Calorimetry Experiment

TL;DR

This work addresses constraints on spin-independent dark matter–baryon interactions by leveraging the XQC rocket calorimeter’s high-altitude, low-shielding environment. It employs a detailed Monte Carlo framework to simulate DM propagation through the atmosphere and the XQC detector, incorporating coherent and incoherent scattering via a nuclear form factor $F(q,R)$ and a cross section $\sigma_\mathrm{Dn}$, yielding predicted recoil spectra as functions of $m_\mathrm{dm}$ and $\sigma_\mathrm{Dn}$. The authors derive a 90%–confidence exclusion region in the $(m_\mathrm{dm},\sigma_\mathrm{Dn})$ plane, showing that the XQC data rule out a wide range of cross sections around the barn scale for $m_\mathrm{dm}$ between $0.01$ and $10^5$ GeV, with features explained by coherent scattering at low masses and form-factor suppression at high masses. They also explore the impact of varying the local DM density and discuss how a future XQC-like mission with lower energy thresholds and longer exposure could extend these constraints, providing a complementary probe to CMB/LSS and other astrophysical limits on strongly interacting DM.

Abstract

Although the rocket-based X-ray Quantum Calorimetry (XQC) experiment was designed for X-ray spectroscopy, the minimal shielding of its calorimeters, its low atmospheric overburden, and its low-threshold detectors make it among the most sensitive instruments for detecting or constraining strong interactions between dark matter particles and baryons. We use Monte Carlo simulations to obtain the precise limits the XQC experiment places on spin-independent interactions between dark matter and baryons, improving upon earlier analytical estimates. We find that the XQC experiment rules out a wide range of nucleon-scattering cross sections centered around one barn for dark matter particles with masses between 0.01 and 10^5 GeV. Our analysis also provides new constraints on cases where only a fraction of the dark matter strongly interacts with baryons.

Figures (9)

• Figure 1: A vertical cross section of an XQC calorimeter. The relative thicknesses of the layers are drawn to scale, as are their relative lengths, but the two scales are not the same. To facilitate the display of the layers, the vertical dimension has been stretched relative to the horizontal dimension.
• Figure 2: A top view of an XQC calorimeter. The absorber is the top layer and underneath it lies the spacer, followed by the pixel body. These dimensions are drawn to scale.
• Figure 3: The points depict the MSIS-E-90 density profiles for the seven most prevalent constituents of the atmosphere above the XQC detector, and the lines show the piecewise exponential fits used in our analysis.
• Figure 4: Top panel: The XQC energy spectrum from 0 - 4 keV in 5 eV bins. This spectrum does not have non-linearity corrections applied (see Ref. big), so the calibration lines at 3312 eV and 3590 eV appear slightly below their actual energies. The cluster of counts to the left of each calibration peak result from X-rays passing through the HgTe layer and being absorbed in the Si components where up to 12% of the energy may then be trapped in metastable states. Bottom panel: The XQC energy spectrum from 0 - 2.5 keV in 5 eV bins. This spectrum, combined with the over-saturation rate of 0.6 events per second with energies greater than 4000 eV, was used in our analysis.
• Figure 5: Simulated event spectra for dark matter particles with masses of 1, 10 and 100 GeV and a total nucleon-scattering cross section of $10^{-27.3}$ cm$^2$. In addition to the events depicted in these spectra, the simulations predict $1300 \pm 160$ events with energies greater than 4000 eV when $m_\mathrm{dm}=10$ GeV and $10,000 \pm 1200$ such events when $m_\mathrm{dm}=100$ GeV. The histogram represents the XQC observations.