Speaker
Описание
The NA64 experiment at CERN was primarily designed in 2015 - 2016 to search for dark photons using the electron beam and missing energy technique. Subsequently the purpose of the experiment was generalized to search for dark sector particles using high-energy beams from the SPS impinging on a thick active target, adopting an experimental strategy based on multiple measurements and the missing energy / missing momentum techniques, employing electron, positron, muon, and hadron (pi/K) beams. While the main experimental technique is still the missing energy / missing momentum one, the active beam dump method was also used (visible mode).
In the electron and positron invisible modes, a high-energy e^\pm beam impinges on an active thick-target (ECAL), in which DS particles may be produced via bremsstrahlung or annihilation processes. The corresponding signal signature is the observation of events with a large missing energy, consisting in the difference between the energy of the primary electron and that measured in the calorimeter. Background events are identified and rejected via a combination of an upstream beam-tagging system - to reject beam contaminants - and a downstream hadronic calorimeter system, to identify penetrating secondaries produced by hard interactions of the primary beam within the target. In the muon mode, a similar approach is adopted to measure events in which DS particles predominantly coupled to second-generation leptons are produced in the target. For this measurement, the detector package is complemented by a dual tracking system before and after the ECAL, to measure for each impinging muon the missing momentum due to the eventual DS production within the target. Finally, in the hadron invisible mode a missing-energy setup is adopted, exploiting charge-exchange reactions within the active target as a source for the production of high-energy neutral mesons, that could eventually invisibly decay to DS states predominantly coupled to quarks.
The NA64 experiment, running at CERN from 2016, reported competitive results from all these scenarios, already excluding the cosmological hypothesis for the origin of DS particles for selected spin/parity combinations of the latter. The final goal of the experiment is to completely scrutinize the DS parameters space before CERN LS4, to confirm or reject this hypothesis for all possible variations of the model.
In this talk, after a brief introduction to the DS physics case, the latest results from the NA64 experiment will be presented, and the future prospects toward the pre-LS4 goal discussed.
