Laboratory limits on solar axions from an ultralow-background germanium spectrometer.

Abstract

Laboratory bounds on the couplings to electrons of light pseudoscalars such as axions, familons, Majorons, etc., are set with an ultralow-background germanium spectrometer using a realistic model for the Sun. In particular Dine-Fischler-Srednicki axion models with F/2${x}_{e}^{\mathcal{'}}$\ensuremath{\lesssim}0.5\ifmmode\times\else\texttimes\fi{}${10}^{7}$ GeV are excluded. It should be emphasized that this is a laboratory bound. It does not rely on a detailed understanding of the dynamics and evolution of red giants, white dwarfs, or other stars as do the more speculative astrophysical bounds which are competitive with our laboratory bound. The lower limit should be improved to F/2${x}_{e}^{\mathcal{'}}$>1.8\ifmmode\times\else\texttimes\fi{}${10}^{7}$ GeV in the near future. It is shown that semiconducting Ge detectors for axions could eventually set limits F/2${x}_{e}^{\mathcal{'}}$${>10}^{8}$ GeV. If discovered, axions or other light weakly interacting bosons would not only allow us to study physics at energies beyond the reach of accelerators but would also provide a new laboratory tool to study the deep interior of stars.