We conduct the first “light-shining-through-wall” (LSW) search for dark photons using two state-of-the-art high-quality-factor superconducting radio frequency (SRF) cavities —Dark SRF—and report the results of its pathfinder run. Our new experimental setup enables improvements in sensitivity over previous searches and covers new dark photon parameter space. We design delicate calibration and measurement protocols to utilize the high-$Q$ setup at Dark SRF. Using cavities operating at 1.3 GHz, we establish a new exclusion limit for kinetic mixing as small as $\epsilon =1.6\times {10}^{-9}$ and provide the world’s best constraints on dark photons in the $2.1\times {10}^{-7}–5.7\times {10}^{-6}\mathrm{eV}$ mass range. Our result is the first proof of concept for the enabling role of SRF cavities in LSW setups, with ample opportunities for further improvements. In addition, our data set a competitive lab-based limit on the standard model photon mass by searching for longitudinal photon polarization.

• Received 28 January 2023
• Accepted 23 May 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.261801

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society