The NA64 experiment's primary objective is to search for unknown particles belonging to a hypothetical "dark sector." These particles could represent dark matter itself or act as mediators of a new force connecting visible matter to dark matter, in addition to gravity. A leading candidate among these particles is the dark photon.
To carry out this search, NA64 uses an electron beam with an energy between 100 and 150 GeV, generated by the Super Proton Synchrotron (SPS), which is directed toward a stationary target. Collisions between electrons in the beam and the target's atomic nuclei could produce dark sector particles. Researchers look for signs of these particles by observing known decay products, such as electrons, or by detecting a loss of energy in the collision, indicating that some of the energy was carried away by invisible particles.
In addition to dark photons, NA64 also searches for axions and axion-like particles. These could explain unresolved symmetry properties of the strong force or act as carriers of a new fundamental interaction. The production of these particles would be investigated through interactions between high-energy photons, generated by the electrons in the beam, and virtual photons emitted by the nuclei in the target.
The experiment also plans to expand its reach by using different types of beams. Using a beam of muons—particles similar to the electron but heavier—also from the SPS, it will search for new particles that interact primarily with muons. This could help solve the mystery of the muon's anomalous magnetic moment, a persistent discrepancy between theory and experiment.
Finally, NA64 plans to use SPS hadron beams to investigate new physics phenomena by searching for invisible decays of neutral kaons and other mesons. These investigations could also help identify mirror-like dark matter candidates.
The Millennium Institute SAPHIR continues to strengthen its presence in frontier experiments at CERN, being one of the most active South American players in the exploration of physics beyond the Standard Model. One of its most significant collaborations is in the NA64 experiment, which searches for signals of exotic particles such as dark photons and other forms of dark matter using electron, muon and positron beams. In this context, researchers linked to SAPHIR have participated in the development and operation of a mobile calibration platform (Moving Table) that allows to adjust with high precision the alignment of the detectors during the tests with particle beams, a key tool to guarantee the quality of the experimental data. In addition, SAPHIR is collaborating in the implementation of the Synchrotron Radiation Detector (SRD), a fundamental technology for positron identification in the new hadron physics program at NA64. This detector contributes to improve the selectivity of the experiment by differentiating positrons from other particles present in the beams, which is essential to achieve the required levels of precision in the search for rare signals. Through this technical and scientific participation, the SAPHIR Millennium Institute not only contributes specialized knowledge, but also consolidates its integration in high-impact international research networks, opening opportunities for young researchers and reinforcing Chile's role in the field of experimental particle physics.