Improved Dark Photon Sensitivity from a Superconducting-Radio-Frequency-Cavity Experiment

We report the refined dark-photon exclusion bound from Dark SRF’s pathfinder run. Our new result is driven by improved theoretical modeling of frequency instability in high-quality resonant experiments. Our analysis leads to a constraint that is an order of magnitude stronger than previously reported (corresponding to a signal-to-noise ratio that is 4 orders of magnitude larger). This result represents the world-leading constraint on non-dark-matter dark photons over a wide range of masses below <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mn>6</a:mn> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi mathvariant="normal">μ</a:mi> <a:mi>eV</a:mi> </a:math> and translates to the best laboratory-based limit on the photon mass <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:mrow> <d:msub> <d:mrow> <d:mi>m</d:mi> </d:mrow> <d:mrow> <d:mi>γ</d:mi> </d:mrow> </d:msub> <d:mo>&lt;</d:mo> <d:mn>2.9</d:mn> <d:mo>×</d:mo> <d:msup> <d:mrow> <d:mn>10</d:mn> </d:mrow> <d:mrow> <d:mo>−</d:mo> <d:mn>48</d:mn> </d:mrow> </d:msup> <d:mtext> </d:mtext> <d:mtext> </d:mtext> <d:mi mathvariant="normal">g</d:mi> </d:mrow> </d:math> .