New Exclusion Limits for Dark Gauge Forces from Beam-Dump Data

We re-analyze proton beam dump data taken at the U70 accelerator at IHEP Serpukhov with the $\nu$-calorimeter I experiment in 1989 to set mass-coupling limits for dark gauge forces. The corresponding data have been used for axion and light Higgs particle searches in Refs. before. We determine new mass and coupling exclusion bounds for dark gauge bosons.