PHYSICAL REVIEW LETTERS 130, 071804 (2023)

ISSN: 0031-9007, SCIE

Search for a Dark Photon and an Invisible Dark Higgs Boson in μ + μ − and Missing Energy Final States with the Belle II Experiment

F. Abudinén et al. (Belle II Collaboration)

The dark photon A0 and the dark Higgs boson h0 are hypothetical particles predicted in many dark sector models. We search for the simultaneous production of A0 and h0 in the dark Higgsstrahlung process eþe− → A0 h0 with A0 → μþμ− and h0 invisible in electron-positron collisions at a center-of-mass energy of 10.58 GeV in data collected by the Belle II experiment in 2019. With an integrated luminosity of 8.34 fb−1, we observe no evidence for signal. We obtain exclusion limits at 90% Bayesian credibility in the range of 1.7–5.0 fb on the cross section and in the range of 1.7 × 10−8–200 × 10−8 on the effective coupling ε2 × αD for the A0 mass in the range of 4.0 GeV=c2 < MA0 < 9.7 GeV=c2 and for the h0 mass Mh0 < MA0 , where ε is the mixing strength between the standard model and the dark photon and αD is the coupling of the dark photon to the dark Higgs boson. Our limits are the first in this mass range.

DOI: 10.1103/PhysRevLett.130.071804

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