Search for solar axions produced by Primakoff conversion using resonant absorption by 169Tm nuclei

The search for resonant absorption of the Primakoff solar axions by 169Tm nuclei have been performed. Such an absorption should lead to the excitation of low-lying nuclear energy level: A+Tm169→Tm∗169→Tm169+γ (8.41 keV). The Si(Li) detector and 169Tm target placed inside the low-background setup were used for that purpose. As a result, a new restriction on the axion–photon coupling and axion mass was obtained: gAγ(GeV−1)⋅mA(eV)⩽1.36×10−5 (90% c.l.). In model of hadronic axion this restriction corresponds to the upper limit on axion mass — mA⩽191 eV for 90% c.l.