Probing the Dark Sector with NA64 and POKER at CERN SPS
Despite its great successes, the Standard Model (SM) of particle physics is far from complete, as suggested by many facts, such as the astrophysical evidences of Dark Matter, the baryon asymmetry observed in the universe and the unsolved problem of the origin of the neutrino masses. The search for DM, in particular, is one of the hottest topics of modern physics. Despite the various astrophysical and cosmological observations proving its existence, its particle properties remain to date unknown. In a theoretically motivated and largely unexplored scenario, DM could interact with the SM through a new force, mediated by a new vector boson (dark photon or $A'$), kinetically mixed with the SM photon.
The NA64-$e$ experiment at CERN aims to produce DM particles using the 100 GeV SPS electron beam impinging on a thick electromagnetic calorimeter. The DM production signature consists in a large observed missing energy, defined as the difference between the energy of the 100 GeV primary electron and the energy deposited in the calorimeter, coupled with no activity in the downstream veto systems. NA64-$e$ its a versatile experiment, featuring a significant sensitivity to several beyond SM extensions involving new feebly interacting particles, as proved by the exclusion limits set by the NA64 collaboration in the ALPs and $L_\mu - L_\tau$ scenarios. In the last years, the collaboration has performed preliminary studies with the aim to run the experiment with a positron beam, in order to exploit the potential of the $e^+ - e ^-$ resonant annihilation for the $A'$ search, according with the ERC-funded POKER (POsitron resonant annihilation into darK mattER) project.
This work presents the latest NA64-$e$ results and its future prospects, reporting the sensitivity of the experiment to different theoretical scenarios. Finally, the progresses and prospects of the POKER project are presented.
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