Search for a dark vector gauge boson decaying to π+π- using η →π+π-γ decays

Abstract

We report a search for a dark vector gauge boson U′ that couples to quarks in the decay chain D∗+→D0π+,D0→KS0η,η→U′γ, U′→π+π-. No signal is found and we set a mass-dependent limit on the baryonic fine structure constant of 10-3-10-2 in the U′ mass range of 290 to 520 MeV/c2. This analysis is based on a data sample of 976 fb-1 collected by the Belle experiment at the KEKB asymmetric-energy e+e- collider.