Recent Results and Future Prospects of the ALPS II Experiment

The axion, originally introduced to solve the strong CP problem, has been a target of many searches in recent years, particularly because it can be cold dark matter. The Any Light Particle Search II (ALPS II), located at DESY in Hamburg, concluded its first science run in 2024 and set new model-independent exclusion limits on the axion-photon coupling 20 times better than previous light shining through a wall experiments. In such experiments, light is directed through a magnetic field where some photons potentially convert into axions. The light is blocked by a strong wall behind the magnet, but the axions may traverse the wall and then be reconverted back into light in another magnetic field and detected. ALPS II employs two 120 meter long strings of 5.3 Tesla HERA dipole magnets. Additionally, it uses a sophisticated optical system consisting of optical cavities to enhance the conversion rates and a heterodyne detector for sensing the weak reconverted field. This talk will present the results of ALPS II's first science run with a highlight on the speaker's work on the data analysis, as well as the plans to improve the experiment's sensitivity by another two orders of magnitude soon. This talk will also discuss the experiment's promising potential for future experiments such as polarimetric searches for vacuum magnetic birefringence, dark matter halo axions, and high-frequency gravitational waves.