New experiment on search for the resonance absorption of solar axion emitted in the M1 transition of $^{83}$Kr nuclei

Axions with an energy of $9.4$ keV emitted in the M1 transition of $^{83}$Kr nuclei in the Sun have been sought in the resonance absorption reaction $A+{^{83}\text{Kr}}\rightarrow{^{83}\text{Kr}^*} \rightarrow {^{83}\text{Kr}} + \gamma,e$ ($9.4$ keV). A proportional gas chamber filled with krypton and placed in a low-background setup at the underground laboratory of the Baksan neutrino observatory was used to detect $\gamma$-ray photons and electrons appearing after the decay of a nuclear level. As a result, a new constraint has been determined on the isoscalar and isovector coupling constants of the axion with nucleons: $|g^3_{AN} - g^0_{AN}|\leq 1.29\times10^{-6}$. This constraint results in the following new bound on the mass of the axion in the hadronic axion model: $m_A\leqslant 100$ eV ($95$% C.L.).