Towards the first axion search results of the Any Light Particle Search II experiment

Abstract

Any Light Particle Search II (ALPS II) is a dual optical cavity enhanced light-shining-through-a-wall (LSW) experiment at DESY in Hamburg looking for axions and axion-like particles with a target search sensitivity of $g_{a \gamma \gamma}$ down to $2 \times 10^{-11}\,\textrm{GeV}^{-1}$ for masses $m_a \leq 0.1\,\textrm{meV}$. Two 120$\,$m long strings of superconducting dipole magnets have been set up, each providing a magnetic field-length product of $560\,\textrm{T}\cdot\textrm{m}$. A resonant optical cavity with a record-worthy storage time of as high as 7$\,$ms has been constructed to encompass one magnet string. During its initial data-taking phase ALPS II will be operated with a simplified optical configuration that facilitates the characterization of the experiment. The first ALPS II science run took place in May/June 2023 and achieved an estimated search sensitivity of $g_{a \gamma \gamma}$ of around $6 \times 10^{-10}\,\textrm{GeV}^{-1}$ for $m_a \leq 0.1\,\textrm{meV}$. Data analysis and further data runs are under way. Final results on axion-photon coupling from the initial science runs of ALPS II are expected in early 2024.