Despite the fact that the existence of dark matter is now supported by numerous astrophysical observations — indicating that it makes up about 85% of the total mass of the Universe — the microscopic nature of this new form of matter remains completely unknown. The experimental investigation of possible new particles and their interactions is one of the broadest and most central topics in contemporary physics.
In this context, the “light dark matter” hypothesis assumes that dark matter consists of particles with a mass similar to or smaller than that of the proton, interacting with ordinary matter through a new force.
The NA64 experiment at CERN investigates the existence of light dark matter by searching for missing energy events. A high-energy electron beam is directed onto a thick active target (an electromagnetic calorimeter), which measures the energy deposited by each incoming particle on an event-by-event basis. The possible production of light dark matter particles through the interaction of the incident electrons with the target material would give rise to events characterized by a large amount of missing energy, defined as the difference between the nominal beam energy and the energy measured by the calorimeter.
So far, NA64 has accumulated about 1×10¹² electrons on target, without observing any signal-like events. This result has made it possible to exclude the existence of light dark matter in a wide region of the parameter space (mass and coupling). The final goal of the experiment for the post-CERN LS3 period (2030–2035) is to complete the experimental investigation by probing the parameter space down to the coupling values predicted by cosmological models.
The Genoa group plays a leading role in the experiment, with responsibilities in detector construction, operation, and data analysis. Since 2022 the group has also promoted a new research line based on the use of a positron beam, exploiting a production mechanism involving the resonant annihilation of positrons with atomic electrons in the target.
The NA64 experiment is co-funded in Italy by the National Institute for Nuclear Physics (INFN).
