Can calorimeters detect single optical phonons with low background?
In plain words
Dark matter between about a hundred and a hundred thousand times lighter than a proton would make a crystal vibrate with only one quantum of vibration energy, a few hundredths of an electron volt. Detectors are not yet sensitive enough to count these single quanta.
Precise statement
Dark matter of mass $m_{\chi} \sim 10\,\mathrm{keV} - 10\,\mathrm{MeV}$ scattering via a dark-photon or hadrophilic mediator excites single optical or acoustic phonons of energy $\omega \sim 10-100\,\mathrm{meV}$ in polar crystals (GaAs, Al2O3, SiO2). The question is whether a phonon sensor (transition-edge sensor, kinetic-inductance detector, superconducting qubit) can reach an energy threshold below 100 meV with dark-count rate below about 1 event/(kg day) at that threshold. An answer is a demonstrated threshold and background, or a proof-of-limit from sensor noise and phonon down-conversion losses.
What would settle it
A calibrated single-phonon-scale threshold measured in a gram-scale crystal underground, with the background rate measured at that threshold.
Status in the literature
Unverified note
TESSERACT (Phys. Rev. Lett. 2025) set first limits for 44-87 MeV dark matter with an athermal phonon detector at eV-scale threshold; single-phonon sensitivity is not demonstrated, and the low-energy excess sets the present background.
See also
- Related Detect single-graviton absorption in a massive acoustic resonator
- Related Unexplained low-energy excess in sensitive detectors
- Related Can daily modulation in anisotropic crystals identify light dark matter?
- Related Can detectors reach the sub-MeV freeze-in dark matter benchmark?
- Related Can single-magnon counting probe spin-coupled sub-MeV dark matter?
- Related Does the Migdal effect occur at the predicted rate in detector media?