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  • Letter
  • Open Access

Optical transitions near the elusive 5s−4f level crossing in highly charged osmium with sensitivity to physics beyond the standard model

Nils-Holger Rehbehn1, Lakshmi Priya Kozhiparambil Sajith1,2, Michael K. Rosner1, Charles Cheung3, Sergey G. Porsev3, Marianna S. Safronova3, Steven Worm2, Dmitry Budker4,5,6,7, Thomas Pfeifer1 et al.

José R. Crespo López-Urrutia1,* and Hendrik Bekker4,5,6,†

  • *Contact author: crespojr@mpi-hd.mpg.de
  • †Contact author: hbekker@uni-mainz.de
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Phys. Rev. A 112, L061101 – Published 5 December, 2025

DOI: https://doi.org/10.1103/p347-47ys

Abstract

Optical transitions in highly charged ions can be very sensitive to hypothetical beyond-the-standard-model phenomena. Those near the degeneracy due to the 5s−4f level crossing are especially promising. We present measurements of Os15,16,17+ ions at an electron beam ion trap and corresponding predictions of several transitions that show a high sensitivity to hypothetical fifth forces and possible violations of local Lorentz invariance. We found electric quadrupole transitions in Os16+, which are suitable for frequency metrology due to linewidths down to 44µHz. Our calculations show the need for including enough inner-shell excitations to avoid an overestimation of interconfiguration transition rates, which were too faint for detection at the present signal-to-noise ratio.

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Phys. Rev. A 112, L061101– Published 5 December, 2025
  • Received 22 September 2025
  • Accepted 7 November 2025
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