Solar axion search with the CAST experiment

The CAST (CERN Axion Solar Telescope) experiment is searching for solar axions by their conversion into photons inside the magnet pipe of a LHC prototype dipole. In the phase II, CAST is operating with a buffer gas inside the magnet bore apertures in order to extent the sensitivity of the experiment to larger axion masses. Preliminary results from the analysis of this second phase with He inside the magnet pipes excludes axions down to $g_{aγ}$ < 2.2 · $10^{−10}GeV^{−1}$ at 95% C.L. for 0.02 eV < $m_{\alpha}$ < 0.39 eV. The data analysis has resulted in the most restrictive experimental limit on the coupling constant of axions to photons and for the first time experimental result has entered the theory motivated axion parameter space. At the beginning of 2008, data started to be taken with He in the magnet pipes in order to extend the sensitivity to axion masses up to 1.2 eV.