Axion Searches in the Past, at Present, and in the Near Future

TL;DR

This work surveys experimental strategies to detect axions and axion-like particles across dark matter, solar, laser-induced, KK-axion, and collider contexts. It emphasizes the Primakoff-based conversion mechanism in magnets, detail increasingly sophisticated coherence control (e.g., buffer gases) and detection technologies, and compares laboratory bounds with astrophysical limits. The paper highlights CAST, ADMX, ALPS, BMV, OSQAR, and KK-axion TPC approaches as leading efforts, discusses the PVLAS hint as a catalyst for new experiments, and outlines near-term prospects that could probe substantial portions of the axion parameter space. The overall message is that a multi-pronged experimental program—spanning resonant cavities, helioscopes, crystal diffraction, vacuum birefringence tests, and large-volume detectors—offers the most comprehensive path to discovering or constraining axions and related particles in the coming years.

Abstract

Theoretical axion models state that axions are very weakly interacting particles. In order to experimentally detect them, the use of colorful and inspired techniques becomes mandatory. There is a wide variety of experimental approaches that were developed during the last 30 years, most of them make use of the Primakoff effect, by which axions convert into photons in the presence of an electromagnetic field. We review the experimental techniques used to search for axions and will give an outlook on experiments planned for the near future.

Figures (26)

• Figure 1: Schematic principle of the microwave cavity experiment to look for cold dark matter axions. First an axion would be resonantly converted into a quasi-monochromatic photon in the magnetic-field permeated microwave cavity. Then an ultra-low-noise receiver is set to detect this photon as an excess on the cavity power output
• Figure 2: Left: Representation of the signal expected in a microwave cavity experiment, where the photon signal appears as an excess over the noise in the power frequency spectrum. The width of the signal would be related with the predicted axion halo velocities. Right: Zoom showing the possible fine structure details in the expected signal
• Figure 3: Left: 2D representation of the axion surface luminosity seen from the Earth ex-Andriamonje:2007ew as a function of the solar radius and the axion energy. Right: Comparison of the solar axion flux calculated using an older version of the standard solar model from 1982 (dashed line) and a more recent version from 2004 one (solid line) ex-bahcall:04a. Here an axion-photon coupling constant of $1 \times 10^{-10}\, {\rm GeV}^{-1}$ is assumed
• Figure 4: Working principle of an axion helioscope. Axions produced in the Sun core by the Primakoff effect would be converted back into photons in a strong magnetic field. Eventually these photons, which have the same energy spectrum as the incoming axions, could be collected by a X-ray detector placed a the end of the magnet field area
• Figure 5: Experimental setup of the CAST experiment at CERN. From the left to the right the Helium cryogenic system, the CAST superconducting magnet, and the tracking system is shown. The tracking system allows to follow the Sun $1.5\,\text{h}$ per day during sunrise and sunset