Kavli Affiliate: T. Higuchi
| First 5 Authors: Belle II Collaboration, F. Abudinén, I. Adachi, L. Aggarwal, H. Aihara
| Summary:
The dark photon $A^prime$ and the dark Higgs boson $h^prime$ are
hypothetical particles predicted in many dark sector models. We search for the
simultaneous production of $A^prime$ and $h^prime$ in the dark Higgsstrahlung
process $e^{+}e^{-}rightarrow A^prime , h^prime$ with $A^prime rightarrow
mu^+mu^-$ and $ h^prime$ invisible in electron-positron collisions at a
center-of-mass energy of 10.58 GeV 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
1.7–5.0 fb on the cross section and in the range $1.7 times10^{-8}$–$200
times10^{-8}$ on the effective coupling $varepsilon^2 times alpha_D$, for
$A^prime$ mass 4.0 GeV/$c^2$ $< M_{A^prime}< 9.7$ GeV/$c^2$ and $h^prime$
mass $M_{h^prime} < M_{A^prime}$, where $varepsilon$ is the mixing strength
between the Standard Model and the dark photon and $alpha_D$ is the coupling
of the dark photon to the dark Higgs boson. Our limits are the first in this
mass range.
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