# Search for production of an invisible dark photon in $\pi^0$ decays

## TL;DR

This paper reports a search for an invisible dark photon produced in neutral pion decays, setting new limits on its coupling and significantly improving constraints on related rare decay processes.

## Contribution

It presents the first search for a dark photon in $ au^0$ decays at the NA62 experiment, establishing new bounds on dark photon properties in the 60--110 MeV/$c^2$ mass range.

## Key findings

- No dark photon signal observed in the data.
- Set upper limits on dark photon coupling strength.
- Improved the limit on the $ au^0 o ext{invisible}$ decay branching ratio.

## Abstract

The results of a search for $\pi^0$ decays to a photon and an invisible massive dark photon at the NA62 experiment at the CERN SPS are reported. From a total of $4.12\times10^8$ tagged $\pi^0$ mesons, no signal is observed. Assuming a kinetic-mixing interaction, limits are set on the dark photon coupling to the ordinary photon as a function of the dark photon mass, improving on previous searches in the mass range 60--110 MeV/$c^2$. The present results are interpreted in terms of an upper limit of the branching ratio of the electro-weak decay $\pi^0 \to \gamma \nu \overline{\nu}$, improving the current limit by more than three orders of magnitude.