arXiv subjects

Michael R. Williams

Publications and source records attributed to Michael R. Williams.

4 recordsLinked to original sources

arXiv2026

Ultralow-Energy Measurements using the Startpoint of $β$ Decays

We propose a novel measurement of $β$ decays using low-temperature solid-state detector technologies. The $β$ startpoint, where the $β$ kinetic energy is zero, offers a unique probe of weak nuclear physics that has not yet been exploited experimentally. We describe how this technique enables searches for heavy sterile neutrinos in the keV--MeV energy range and show that, with current technologies, sensitivities to sterile neutrino coupling to electrons can be achieved that exceed the current best constraints. The spectrum produced by the recoiling daughter ion also offers a calibration of the nuclear recoil response, addressing key assumptions in sub-GeV dark matter searches. We outline a potential experimental scheme using neutron activation to produce $^{32}$P $\textit{in situ}$ in a silicon substrate, discuss projected sensitivities to sterile neutrinos, and evaluate the prospects for nuclear recoil calibrations.

hep-ex↗

arXiv2026

Photon Calibration Techniques for High Resolution Cryogenic Detectors

Monoenergetic photons from a pulsed laser diode or LED are commonly used to calibrate the detector response of high-resolution calorimetric detectors. However, when the detector's resolution is larger than the energy of a single photon, a calibration is normally derived using Poisson statistics. In this paper, we clarify the assumptions implicit in this calibration method, before considering how a more realistic model of a detector's performance will violate these assumptions, biasing the calibration. Finally, we judge the individual impact of specific detector parameters on our calibration, and conclude with discussion of both the limits of our calculations and the implications for state-of-the art detectors.

physics.ins-det↗

arXiv2025

Low Energy Backgrounds and Excess Noise in a Two-Channel Low-Threshold Calorimeter

We describe observations of low energy excess (LEE) events, background events observed in all light dark matter direct detection calorimeters, and noise in a Transition Edge Sensor based two-channel silicon athermal phonon detector with 375 meV baseline energy resolution. We measure two distinct LEE populations: ``shared'' multichannel events with a pulse shape consistent with substrate athermal phonon events, and sub-eV events that couple nearly exclusively to a single channel with a significantly faster pulse shape. These ``singles'' are consistent with events occurring within the aluminum athermal phonon collection fins. Similarly, our measured detector noise is higher than the theoretical expectation. Measured noise can be split into an uncorrelated component, consistent with shot noise from small energy depositions within the athermal phonon sensor itself, and a correlated component, consistent with shot noise from energy depositions within the silicon substrate's phonon system.

physics.ins-det↗

arXiv2024

A Stress Induced Source of Phonon Bursts and Quasiparticle Poisoning

The performance of superconducting qubits is degraded by a poorly characterized set of energy sources breaking the Cooper pairs responsible for superconductivity, creating a condition often called ``quasiparticle poisoning". Both superconducting qubits and low threshold dark matter calorimeters have observed excess bursts of quasiparticles or phonons that decrease in rate with time. Here, we show that a silicon crystal glued to its holder exhibits a rate of low-energy phonon events that is more than two orders of magnitude larger than in a functionally identical crystal suspended from its holder in a low-stress state. The excess phonon event rate in the glued crystal decreases with time since cooldown, consistent with a source of phonon bursts which contributes to quasiparticle poisoning in quantum circuits and the low-energy events observed in cryogenic calorimeters. We argue that relaxation of thermally induced stress between the glue and crystal is the source of these events.

physics.ins-det↗