The Any Light Particle Search Experiment at DESY

Abstract

The Any Light Particle Search (ALPS II) is a light shining through a wall (LSW) experiment searching for axion-like elementary particles in the sub-eV mass range, which are motivated by astrophysics and cosmology and fulfill the requirements for being dark matter. ALPS II aims to measure an axion-to-photon coupling of $2\times 10^{-11}\textrm{ GeV}^{-1}$, which is several orders of magnitude better than that of previous LSW experiments and will thus investigate a new parameter range. The increased performance is achieved by enhancing the magnetic field interaction length to $2\times 10^{6}$ m and by amplifying the signal in an optical cavity on each side of a light-tight barrier. The expected signal is in the order of 1 photon per day, which will be measured by photon detectors with very low dark count rates of $\mathcal{O}(10^{-6}\textrm{ Hz})$. This article gives a technical overview on the experiment design, previous and ongoing investigations, and the current status with focus on the single photon detection