engleski

New solar axion search using the CERN Axion Solar Telescope with He-4 filling

The CERN Axion Solar Telescope (CAST) searches for a -> gamma conversion in the 9 T magnetic field of a refurbished LHC test magnet that can be directed toward the Sun. Two parallel magnet bores can be filled with helium of adjustable pressure to match the x-ray refractive mass m_gamma to the axion search mass m_a. After the vacuum phase (2003-2004), which is optimal for m_a less than or similar to 0.02 eV, we used He-4 in 2005-2007 to cover the mass range of 0.02-0.39 eV and He-3 in 2009-2011 to scan from 0.39 to 1.17 eV. After improving the detectors and shielding, we returned to He-4 in 2012 to investigate a narrow m_a range around 0.2 eV ("candidate setting" of our earlier search) and 0.39-0.42 eV, the upper axion mass range reachable with He-4, to "cross the axion line" for the KSVZ model. We have improved the limit on the axion-photon coupling to g_a_gamma < 1.47 x 10^(-10) GeV^(-1) (95% C.L.), depending on the pressure settings. Since 2013, we have returned to the vacuum and aim for a significant increase in sensitivity.

strong cp problem ; coherent conversion ; cast experiment ; magnetic-field ; invariance ; detectors ; photons

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