Search for dark photon decays to $\mu^+\mu^-$ at NA62

• DOI: 10.48550/arxiv.2303.08666
• Publication Date: 2023-01-01
• Authors: NA62 Collaboration
• Keywords: High Energy Physics - Experiment (hep-ex); FOS: Physical sciences; 7. Clean energy; High Energy Physics - Experiment

The NA62 experiment at CERN, designed to study the ultra-rare decay $K^+ \to π^+ν\overlineν$, has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to $μ^+μ^-$ pairs is reported, based on a sample of $1.4 \times 10^{17}$ protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV$/c^2$.<br/>23 pages, 16 figures, final version, accepted for publication in JHEP<br/>