{CERN} Axion Solar Telescope
Previous solar axion searches have been carried out in Brookhaven (1990) and in Tokyo (2000), tracking the Sun with a dipole magnet. The solar neutrino anomaly amply demonstrates that the Sun is a very useful source of weakly interacting particles for fundamental research. Axions can be produced in the Sun’s core through the scattering of thermal photons in the Coulomb field of electric charges (Primakoff effect). In a transverse magnetic field the Primakoff effect can work in reverse, coherently converting the solar axions back into X-ray photons of a few keV. The conversion efficiency increases with (B L)2. In the CAST experiment an LHC prototype dipole magnet (B=9 T and L=10 m) with straight beam pipes provides a conversion efficiency exceeding that of the two earlier solar axion telescopes by almost a factor of 100. This magnet is mounted on a moving platform and coupled to both gas filled and solid-state low-background X-ray detectors on either end allowing it to observe the Sun for nearly 1.5 hours at both sunrise and sunset. The rest of the day will be devoted to background measurements and, because of the Earth motion, to observations of a large portion of the sky. The 42 mm aperture of the LHC magnet beam pipe requires correspondingly large X-ray detectors, implying a large level of noise. To overcome this problem, CAST will use an X-ray mirror system from the German space program, the converted X-rays will be focused to a ~1.5 mm spot, improving the signal-to-noise ratio significantly over the original CAST proposal and the earlier solar axion telescopes. CAST has the potential to reach an axion detection sensitivity about ten times higher than that of the previous experiments, extending for the first time, the axion searches beyond the limit dictated by astrophysical considerations. In addition, because of the lower threshold, CAST will also be able to search for axions in an energy region previously inaccessible, leaving room for possible surprises. astro
Classification: Dark matter search experiments › Axion search experiments
People in this graph
- Karl van Bibber (25 papers)