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arXiv · 1503.00610

New solar axion search in CAST with $^4$He filling

Abstract

The CERN Axion Solar Telescope (CAST) searches for $a\to\gamma$ 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 $m_a\lesssim0.02$ eV, we used $^4$He in 2005--2007 to cover the mass range of 0.02--0.39 eV and $^3$He in 2009--2011 to scan from 0.39--1.17 eV. After improving the detectors and shielding, we returned to $^4$He 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 $^4$He, to "cross the axion line" for the KSVZ model. We have improved the limit on the axion-photon coupling to $g_{a\gamma}< 1.47\times10^{-10} {\rm GeV}^{-1}$ (95% C.L.), depending on the pressure settings. Since 2013, we have returned to vacuum and aim for a significant increase in sensitivity.

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M. Arik, S. Aune, K. Barth, A. Belov, H. Bräuninger, J. Bremer, V. Burwitz, G. Cantatore, J. M. Carmona, S. A. Cetin, J. I. Collar, E. Da Riva, T. Dafni, M. Davenport, A. Dermenev, C. Eleftheriadis, N. Elias, G. Fanourakis, E. Ferrer-Ribas, J. Galán, J. A. García, A. Gardikiotis, J. G. Garza, E. N. Gazis, T. Geralis, E. Georgiopoulou, I. Giomataris, S. Gninenko, M. Gómez Marzoa, M. D. Hasinoff, D. H. H. Hoffmann, F. J. Iguaz, I. G. Irastorza, J. Jacoby, K. Jakovčić, M. Karuza, M. Kavuk, M. Krčmar, M. Kuster, B. Lakić, J. M. Laurent, A. Liolios, A. Ljubičić, G. Luzón, S. Neff, T. Niinikoski, A. Nordt, I. Ortega, T. Papaevangelou, M. J. Pivovaroff, G. Raffelt A. Rodríguez, M. Rosu, J. Ruz, I. Savvidis, I. Shilon, S. K. Solanki, L. Stewart, A. Tomás, T. Vafeiadis, J. Villar, J. K. Vogel, S. C. Yildiz, K. Zioutas. 2015-03-02. New solar axion search in CAST with $^4$He filling. https://doi.org/10.1103/physrevd.92.021101

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