Phys. Rev. D 109, 112015 (2024)

ISSN: 2470-0010, SCIE

Search for a 𝜇+⁢𝜇− resonance in four-muon final states at Belle II

Belle II Collaboration (I. Adachi, ..., N. Anh Ky, ...)

We report on a search for a resonance X decaying to a pair of muons in eþe− → μþμ−X events in the 0.212–9.000 GeV=c2 mass range, using 178 fb−1 of data collected by the Belle II experiment at the SuperKEKB collider at a center of mass energy of 10.58 GeV. The analysis probes two different models of X beyond the standard model: a Z0 vector boson in the Lμ − Lτ model and a muonphilic scalar. We observe no evidence for a signal and set exclusion limits at the 90% confidence level on the products of cross section and branching fraction for these processes, ranging from 0.046 fb to 0.97 fb for the Lμ − Lτ model and from 0.055 fb to 1.3 fb for the muonphilic scalar model. For masses below 6 GeV=c2 , the corresponding constraints on the couplings of these processes to the standard model range from 0.0008 to 0.039 for the Lμ − Lτ model and from 0.0018 to 0.040 for the muonphilic scalar model. These are the first constraints on the muonphilic scalar from a dedicated search.

DOI: https://doi.org/10.1103/PhysRevD.109.112015