The Any Light Particle Search experiment at DESY

TL;DR

The ALPS II experiment at DESY searches for axion-like particles using an advanced light shining through a wall setup, aiming to detect extremely weak signals and improve sensitivity over previous experiments in the quest for dark matter candidates.

Contribution

This paper presents the design, technical advancements, and current status of the ALPS II experiment, significantly enhancing sensitivity to axion-like particles compared to prior LSW experiments.

Findings

Enhanced magnetic field interaction length to 2×106 m

Implementation of optical cavities for signal amplification

Achieved low dark count photon detection rates

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 $2\times 10^{-11}\,\mathrm{GeV^{-1}}$, 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 $\times$ 106\,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 $\mathcal O(10^{-6}\,\mathrm{Hz})$. 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.