# Dark matter search in missing energy events with NA64

## TL;DR

The NA64 experiment searched for sub-GeV dark matter mediated by a dark photon in missing energy events and set new constraints on its properties, demonstrating the effectiveness of active beam dump methods.

## Contribution

This work provides the most stringent constraints to date on dark photon mixing and dark matter parameter space below 0.2 GeV using an active beam dump approach.

## Key findings

- No evidence of dark photon production was observed.
- New limits on dark photon mixing strength were established.
- Constraints on scalar and fermionic dark matter models were improved.

## Abstract

A search for sub-GeV dark matter production mediated by a new vector boson $A'$, called dark photon, is performed by the NA64 experiment in missing energy events from 100 GeV electron interactions in an active beam dump at the CERN SPS. From the analysis of the data collected in the years 2016, 2017, and 2018 with $2.84\times10^{11}$ electrons on target no evidence of such a process has been found. The most stringent constraints on the $A'$ mixing strength with photons and the parameter space for the scalar and fermionic dark matter in the mass range $\lesssim 0.2$ GeV are derived, thus demonstrating the power of the active beam dump approach for the dark matter search.