Searching for Dark Matter Axions via Atomic Excitations

Abstract

Axions can be considered as good dark matter candidates. The detection of such light particles can be achieved by observing axion-induced atomic excitations. The target is in a magnetic field so that the m-degeneracy is removed, and the energy levels can be suitably adjusted. Using an axion-electron coupling indicated by the limit obtained by the Borexino experiment, which is quite stringent, reasonable axion absorption rates have been obtained for various atomic targets The obtained results depend, of course, on the atom considered through the parameters ϵ (the spin−orbit splitting) as well as δ ( the energy splitting due to the magnetic moment interaction). This assumption allows axion masses in the tens of μeV if the transition occurs between members of the same multiplet, i.e., |J1,M1=−J1⟩→|J1,M1=−J+1⟩,J1≠0, and axion masses in the range 1 meV–1 eV for transitions of the spin−orbit splitting type |J1,M=−J1⟩→|J2,M2=−J1+q⟩,q=−1,0,1, i.e., three types of transition. The axion mass that can be detected is very close to the excitation energy involved, which can vary by adjusting the magnetic field. Furthermore, since the axion is absorbed by the atom, the calculated cross-section exhibits the behavior of a resonance, which can be exploited by experiments to minimize any background events.