KARLA A.ALAMO-MART′I NEZ We study the very rich globular cluster(GC)system in the massive galaxy cluster Abell 1689,with the goals of testing the existence of a universal et(GC formation efficiency per total mass,εt=MGC/Mtotal)in an extreme system,and exploring the relationship between GCs and dark matter.Using HST/ACS data in the F814W filter,we estimate that the total number of GCs within a projected radius of 400kpc is~163000.This is the largest GC population found to date.From the surface number density of GCs,the galaxy luminosity model,the lensing-derived mass distribution,and the X-ray emitting gas,we estimate the mass of each of these components,and construct its projected radial mass profile.We calculate the radial profile of et,and find that the previous values from the literature are consistent with ours when comparing within the same physical radius.On the other hand,εt varies with radius in a manner that appears similar for different clusters.We conclude that,although the GC formation efficiency is not universal,the GCs are good tracers of the total mass(baryonic and non-baryonic).It seems that the dark matter halo density governs the GC formation efficiency.