Search for resonant absorption of solar axions emitted in an M1 transition in 57Fe nuclei

The resonant absorption of solar axions by 57 Fe nuclei, which is accompanied by the excitation of the first excited nuclear level: A + 57 Fe → 57 Fe* → 57 Fe + γ(14.4 keV), is sought. To seek 14.4-keV photons, a Si(Li) detector and an enriched 57 Fe target are used. The detector and target are placed in a low-background setup equipped with passive and active shieldings. As a result, a new upper limit m A ≤ 360 eV (at 90% C.L.) has been determined for the axion mass.