The red-giant branch (RGB) in globular clusters is extended to larger brightness if the degenerate helium core loses too much energy in ``dark channels.'' Based on a large set of archival observations, we provide high-precision photometry for the Galactic globular cluster M5 (NGC 5904), allowing for a detailed comparison between the observed tip of the RGB with predictions based on contemporary stellar evolution theory. In particular, we derive 95% confidence limits of ${g}_{ae}<4.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ on the axion-electron coupling and ${\ensuremath{\mu}}_{\ensuremath{\nu}}<4.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}{\ensuremath{\mu}}_{B}$ (Bohr magneton ${\ensuremath{\mu}}_{B}=e/2{m}_{e}$) on a neutrino dipole moment, based on a detailed analysis of statistical and systematic uncertainties. The cluster distance is the single largest source of uncertainty and can be improved in the future.

Neutrino and Axion Bounds from the Globular Cluster M5 (NGC 5904)