  The amount of mass lost by stars during the red-giant branch (RGB) phase is
one of the main parameters to understand and correctly model the late stages of
stellar evolution. Nevertheless, a fully-comprehensive knowledge of the RGB
mass loss is still missing.
  Galactic Globular Clusters (GCs) are ideal targets to derive empirical
formulations of mass loss, but the presence of multiple populations with
different chemical compositions has been a major challenge to constrain stellar
masses and RGB mass losses. Recent work has disentangled the distinct stellar
populations along the RGB and the horizontal branch (HB) of 46 GCs, thus
providing the possibility to estimate the RGB mass loss of each stellar
population. The mass losses inferred for the stellar populations with pristine
chemical composition (called first-generation or 1G stars) tightly correlate
with cluster metallicity. This finding allows us to derive an empirical RGB
mass-loss law for 1G stars.
  In this paper we investigate seven GCs with no evidence of multiple
populations and derive the RGB mass loss by means of high-precision {\it
Hubble-Space Telescope} photometry and accurate synthetic photometry.
  We find a cluster-to-cluster variation in the mass loss ranging from
$\sim$0.1 to $\sim$0.3 $M_{\odot}$.
  The RGB mass loss of simple-population GCs correlates with the metallicity of
the host cluster. The discovery that simple-population GCs and 1G stars of
multiple population GCs follow similar mass-loss vs. metallicity relations
suggests that the resulting mass-loss law is a standard outcome of stellar
evolution.
