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The impact of metallicity on the mass-loss rate from red giant branch (RGB)stars is studied through its effect on the parameters of horizontal branch (HB)stars. The scaling factors from Reimers (1975) and Schroder & Cuntz (2005) aredetermined for 56 well-studied Galactic globular clusters (GCs). The medianvalues among clusters are, respectively, {\eta}_R = 0.477 +/- 0.070(+0.050/-0.062) and {\eta}_SC = 0.172 +/- 0.024 (+0.018/-0.023) (standarddeviation and systematic uncertainties, respectively). Mass-loss mechanisms onthe RGB have very little metallicity dependence: over a factor of 200 in ironabundance, {\eta} varies by <~30 per cent, within the current systematicuncertainties on cluster ages and evolution models. Since {\eta} incorporatescluster age, the low standard deviation of {\eta} among clusters (~14 per cent)suggests that age can almost entirely account for the "second parameterproblem". The remaining spread in {\eta} correlates with cluster mass anddensity, suggesting helium enrichment provides the third parameter explainingHB morphology of GCs. The metallicity variation is reduced further if globularclusters are more co-eval than generally thought. This would also betterreproduce the observed AGB tip luminosities, which are not well modelled byextrapolating the RGB {\eta} to later evolutionary epochs.

Mass loss on the red giant branch: the value and metallicity dependence of Reimers' {\eta} in globular clusters