Search for the dark photon in $π^0$ decays by the NA48/2 experiment at CERN

Abstract

A sample of $4.687\times 10^6$ fully reconstructed $K^\pm\toπ^\pmπ^0_D$, $π^0_D\toγe^+e^-$ decay candidates in the kinematic range $m_{ee}>10~{\rm MeV}/c^2$ 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 $K^\pm\toπ^\pmπ^0$, $π^0\toγA'$, $A'\to e^+e^-$. No signal is observed, and preliminary exclusion limits on space of dark photon mass $m_A'$ and mixing parameter $\varepsilon^2$ are reported.