ALPS II reports improved axion search sensitivity without a detection

The ALPS II collaboration reported that its first science campaign was more than 20 times more sensitive to hypothetical axion particles than previous experiments of the same kind. The results, posted as a preprint, found no evidence for axions. The apparatus uses magnetic fields to try to convert laser photons into axions that could pass through an opaque wall, then convert them back into detectable light. The campaign ran from February to May 2024. An apparent excess signal was very likely caused by stray light reaching the detector at two photons per hour.