Search for the dark photon in π0 decays by the NA48/2 experiment at CERN

Abstract

A sample of 4.687 × 106 fully reconstructed K+ → π+π0D, π0D → γe+e- decay candidates in the kinematic range mee > 10 MeV/c2 with a negligible background contamination collected by the NA48/2 experiment at CERN in 2003-04 is analysed to search for the dark photon (A') via the decay chain K+ → π+π0, π0 → γA', A' → e+e-. No signal is observed, and preliminary exclusion limits on space of dark photon mass m'A and mixing parameter ϵ2 are reported.