Any Light Particle Searches with ALPS II: Description of the first science campaign

TL;DR

ALPS II's first science campaign used light-shining-through-a-wall technique to search for beyond-Standard-Model bosons, achieving high sensitivity but finding no evidence of new particles.

Contribution

First experimental results from ALPS II using advanced optical and magnet setups to search for pseudo-Goldstone bosons beyond the Standard Model.

Findings

No evidence for new bosons was observed.

Photon-boson conversion sensitivity reached 10^{-13}.

Optical system upgrades aim to improve sensitivity by four orders of magnitude.

Abstract

From February to May of 2024 the Any Light Particle Search II (ALPS II) conducted its first science campaign using the `light-shining-through-a-wall' technique to search for pseudo-Goldstone bosons that lie beyond the Standard Model of particle physics and which are inaccessible by accelerator-based experiments. The experimental setup consists of two strings of superconducting dipole magnets, each more than 100 m long, that are separated by a wall. Laser light is directed through the first magnet string and a heterodyne detection system is used to measure the electromagnetic power that traverses a wall via the conversion to and then from a bosonic field. After the wall, a high-finesse optical cavity resonantly enhances the signal power. Two searches were carried out, one with the laser polarized perpendicular to the magnetic field direction and another with its polarization state aligned parallel to the magnetic field. No evidence for the existence of new bosons was found. In its first science campaign, ALPS II reached photon-boson conversion probability sensitivities of a few $10^{-13}$. The ongoing upgrade of the optical system aims to increase this sensitivity by about four orders of magnitude.