Search for solar axions emitted in an M1 transition in 7Li* nuclei

The resonance absorption of solar axions by ⁷Li nuclei, which is accompanied by the excitation of the first nuclear level of lithium a + ⁷Li → ⁷Li* → ⁷Li + γ, is sought. To this end, the energy spectrum has been measured by an HPGe detector that is surrounded by a LiOH layer. A new upper limit m _a ≤ 16 keV (at 90% C.L.) has been determined for the mass of the hadron axion.