Searching for dark matter with the Th-229 nuclear lineshape from laser spectroscopy

TL;DR

This paper explores using laser spectroscopy of Th-229 nuclear lineshape to detect ultralight dark matter, promising to improve sensitivity beyond current atomic clock bounds and set new constraints on dark matter models.

Contribution

It introduces a novel method leveraging Th-229 nuclear excitation spectra for dark matter detection and provides initial experimental constraints from recent laser excitation data.

Findings

First dark matter search using Th-229 excitation spectrum.

Current constraints are below existing clock experiment sensitivities.

Projected measurements will surpass current bounds.

Abstract

The recent laser excitation of the low-lying Th-229 isomer transition is starting a revolution in ultralight dark matter searches. The enhanced sensitivity of this transition to the large class of dark matter models dominantly coupling to quarks and gluons will ultimately allow us to probe coupling strengths eight orders of magnitude smaller than the current bounds from optical atomic clocks, which are mainly sensitive to dark matter couplings to electrons and photons. We argue that, with increasing precision, observations of the Th-229 excitation spectrum will soon give world-leading constraints. Using data from the pioneering laser excitation of Th-229 by Tiedau et al. [Phys. Rev. Lett. 132, 182501 (2024)], we present a first dark matter search in the excitation spectrum. While the exclusion limits of our detailed study of the lineshape are still below the sensitivity of currently operating clock experiments, we project the measurement of Zhang et al. [Nature 663, 63 (2024)] to surpass it.