{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"2956a44869a19de068775222f18643f320209e8b33b0e2c023c6a8f9fded5e5f","created":"2026-10-03T07:18:05Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"181d45373fed1c713003bf2740e04e6ac770df7602ac0dfca7aaa809402ee87c","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"hep.sub-gev-detection.single-phonon-calorimetry","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"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.","posed_since":"","precise":"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.","problem_ref":null,"references":"","settled_by":"A calibrated single-phonon-scale threshold measured in a gram-scale crystal underground, with the background rate measured at that threshold.","status_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.","title":"Can calorimeters detect single optical phonons with low 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