Search for 8.4-keV Solar Axions Emitted in the M1 Transition in 169Tm Nuclei

Abstract

Axions with an energy of 8.4 keV emitted in the М1 transition in 169Tm nuclei in the Sun are sought in the $$A + {{\;}^{{169}}}{\kern 1pt} {\text{Tm}}$$ → 169Tm* → $$^{{169}}{\text{Tm}} + (\gamma ,e)$$ (8.4 keV) reaction of resonant absorption by 169Tm nuclei on the Earth using a $${\text{T}}{{{\text{m}}}_{{\text{3}}}}{\text{A}}{{{\text{l}}}_{{\text{5}}}}{{{\text{O}}}_{{{\text{12}}}}}$$ thulium garnet crystal as a bolometric detector. The flux of monochromatic 8.4‑keV axions has been calculated. New constraints on the axion–nucleon coupling constants have been obtained and, as a result, new upper bounds on the axion mass $$m_{A}^{{{\text{KSVZ}}}} \leqslant {\text{141}}$$ eV and $$m_{A}^{{{\text{DFSZ}}}} \leqslant {\text{244}}$$ eV have been obtained at 90% C.L. in the KSVZ and DFSZ models, respectively.