{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"5d0297fa21afd2b532ba2a48617cfa70cdd246896954fa3d684d1f10763e8e76","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b","e0f309a65d83f23efd1242f6a4e4fd2f6025683cb46e0c1bc8610eae28a088ab"],"salt":"d170adef8505e575ce89c6b0f54c76f9f89fa2e66d59dac6006228b13487b768","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":"2","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, $\\mathrm{Al_2O_3}$, $\\mathrm{SiO_2}$). 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":"e0f309a65d83f23efd1242f6a4e4fd2f6025683cb46e0c1bc8610eae28a088ab","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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