Search for Sub-eV Mass Solar Axions by the CERN Axion Solar Telescope with ~3He Buffer Gas

摘要

The CERN Axion Solar Telescope (CAST) has extended its search for solar axions by using ~3He as a buffer gas. At T = 1.8 K this allows for larger pressure settings and hence sensitivity to higher axion masses than our previous measurements with ~4He. With about 1 h of data taking at each of 252 different pressure settings we have scanned the axion mass range 0.39 eV ≤ m_a ≤ 0.64 eV. From the absence of excess x rays when the magnet was pointing to the Sun we set a typical upper limit on the axion-photon coupling of g_(aγ) ≤ 2.3 × 10~(10) GeV~(-1) at 95% C.L., the exact value depending on the pressure setting. Kim-Shifman-Vainshtein-Zakharov axions are excluded at the upper end of our mass range, the first time ever for any solar axion search. In the future we will extend our search to m_a ≤1.15 eV, comfortably overlapping with cosmological hot dark matter bounds.