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At the DESY lab, the ALPS II experiment was launched to hunt for axions — hypothetical ghost particles that might make up dark matter. This invisible mass acts like a skeleton, preventing galaxies from flying apart due to their spin. Discovering the axion would mean a breakthrough beyond the current table of elementary particles. The setup 'shines through a wall': a super-powerful laser fires at an opaque barrier, hoping that some light will briefly turn into ghosts and leak through to be detected on the other side. Over four months, more photons were sent through the wall than there are stars in the observable universe, but not a single one transformed into an axion. That's not a failure, though — the instrument worked perfectly and tightened the limits on how strongly axions interact with light by a factor of 20. Now the system is being upgraded: mirrors and laser are being improved to boost sensitivity another hundredfold.

Original abstract

as written by the authors arXiv:2512.14110

The light-shining-through-a-wall experiment ALPS II at DESY in Hamburg searched for axions and similar lightweight particles in its first science campaign from February to May 2024. No evidence for the existence of such particles was found. For pseudoscalar bosons like the axion, with masses below about 0.1 meV, we achieved a limit for the di-photon coupling strength of 1.5e-9 1/GeV at a 95% confidence level. This is more than a factor of 20 improvement compared to all previous similar experiments. We also provide limits on photon interactions for scalar, vector and tensor bosons. An achievement of this first science campaign is the demonstration of stable operation and robust calibration of the complex experiment. Currently, the optical system of ALPS II is being upgraded aiming for another two orders of magnitude sensitivity increase.