Dark sector searches with the NA64/POKER experiment at CERN

by Andrea Celentano (INFN Genova)

Thursday 5 Jun 2025, 11:00 → 12:00 Europe/Rome

Aula R (Dipartimento di Fisica e Astronomia - Edificio Marzolo)

One of the strongest motivations to search for physics beyond the Standard Model (SM) is explaining the nature of Dark Matter (DM). Despite extensive direct, indirect, and collider searches, no conclusive results have been found. A compelling DM candidate is Light Dark Matter (LDM), with masses between 1–1000 MeV, which becomes viable if a new interaction mechanism with SM particles is introduced. A simple model adds a new vector boson (Dark Photon, $A^\prime$) that mixes weakly with the SM photon and couples to DM. The $A^\prime$ can be produced in charged particle interactions and decay to LDM pairs.

The NA64 experiment at CERN uses a 100 GeV electron beam on a thick active target (ECAL) to search for $A^\prime$ production. If produced, the LDM particles escape undetected, resulting in measurable missing energy. NA64 looks for such events with no downstream veto activity. With $10^{13}$ electrons-on-target and no signal observed, NA64 has set the most competitive limits in the LDM parameter space. A complementary positron beam measurement—supported by the POKER ERC project—was also performed to exploit the annihilation channel. Two successful tests at 100 and 70 GeV demonstrated the feasibility of this approach and motivate a high-statistics program post-LS3.

NA64 has also launched a parallel program using a 160 GeV muon beam to explore higher-mass LDM ($\gtrsim 300$ MeV), where electron/positron sensitivity decreases. This strategy involves precise momentum measurements before and after the target to identify missing momentum from LDM production. A successful pilot run in 2022 with $2 \times 10^{12}$ muons-on-target confirmed the potential of this technique.