Search for sub-eV mass solar axions by the CERN axion solar telescope with He3 buffer gas

Abstract

The CERN Axion Solar Telescope (CAST) has extended its search for solar axions by using He3 as a buffer gas. At T=1.8K this allows for larger pressure settings and hence sensitivity to higher axion masses than our previous measurements with He4. With about 1 h of data taking at each of 252 different pressure settings we have scanned the axion mass range 0.39eVm a0.64eV. 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 aγ2.3×10 -10GeV -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 a1.15eV, comfortably overlapping with cosmological hot dark matter bounds. Published by the American Physical Society under the terms of the http://creativecommons.org/licenses/by/3.0/Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.