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

TL;DR

This study searches for dark photons in kaon decays using a large dataset from the NA48/2 experiment, setting new exclusion limits on dark photon parameters without observing a signal.

Contribution

It provides the first search for dark photons in kaon decays with a large dataset, establishing new exclusion limits on dark photon mass and mixing parameters.

Findings

No dark photon signal observed.

Preliminary exclusion limits set on dark photon parameters.

Large dataset of kaon decay events analyzed.

Abstract

A sample of $4.687\times 10^6$ fully reconstructed $K^\pm\to\pi^\pm\pi^0_D$, $\pi^0_D\to\gamma e^+e^-$ 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 $K^\pm\to\pi^\pm\pi^0$, $\pi^0\to\gamma A'$, $A'\to e^+e^-$. No signal is observed, and preliminary exclusion limits on space of dark photon mass $m_A'$ and mixing parameter $\varepsilon^2$ are reported.