Prospects of solar axion searches with crystal detectors

A calculation of the expected signal due to Primakoff coherent conversion of solar axions into photons via Bragg scattering in several crystal detectors is presented. The results are confronted with the experimental sensitivities of present and future experiments concluding that the sensitivity of crystal detectors does not challenge the globular cluster limit on the axion-photon coupling g_aγγ. In particular, in the axion mass window m_a 0.03 eV explored with this technique (not accessible at present by other methods), g_aγγ might be constrained down to 10⁻⁹ GeV⁻¹ (the recent helioseismological bound) provided that significant improvements in the parameters and performances of these detectors be achieved and large statistics accumulated. This bound should be considered as a minimal goal for the sensitivity of future crystal experiments. Consequently, finding a positive signal at this level of sensitivity would necessarily imply revisiting other more stringent astrophysical limits derived for the same range of m_a values.