First Experimental Bounds on Transverse Plasmon Solar Axions with ANAIS-112

Abstract

Solar axion-like particles (ALPs) can be resonantly produced through the conversion of transverse plasmons in the magnetic field of the solar interior, introducing a production mechanism complementary to the conventional Primakoff process. In this Letter, we report the first experimental search for solar ALPs produced through this mechanism. Using an exposure of 625.75 kg$\times$yr from ANAIS-112, we search for the annual modulation of the flux induced by the variation of the Earth--Sun distance, assuming detection through inverse Primakoff conversion in the detector. Modulation amplitudes fitted in 1 keV bins between 1--20 keV are consistent with the absence of modulation, yielding the first constraints on the axion--photon coupling that include the resonant transverse-plasmon flux, $g_{a{\hat{I}}^3}<1.32\times 10^{-9}{\mathrm{GeV}}^{-1}$ (90\% C.L.) at $m_a\simeq 150$ eV. This previously unexplored production channel extends the sensitivity of ANAIS-112 in the mass range 35--280 eV, where, for the expected solar magnetic-field models, the transverse-plasmon flux exceeds the Primakoff flux by up to two orders of magnitude.

4 pages 3 figures main text, 4 pages 5 figures Supplemental Material

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