Kavli Affiliate: T. Higuchi
| First 5 Authors: Belle II Collaboration, I. Adachi, L. Aggarwal, H. Ahmed, H. Aihara
| Summary:
Inelastic dark matter models that have two dark matter particles and a
massive dark photon can reproduce the observed relic dark matter density
without violating cosmological limits. The mass splitting between the two dark
matter particles $chi_{1}$ and $chi_{2}$, with $m(chi_{2}) > m(chi_{1})$,
is induced by a dark Higgs field and a corresponding dark Higgs boson
$h^{prime}$. We present a search for dark matter in events with two vertices,
at least one of which must be displaced from the interaction region, and
missing energy. Using a $365,mbox{fb}^{-1}$ data sample collected at Belle
II, which operates at the SuperKEKB $e^+e^-$ collider, we observe no evidence
for a signal. We set upper limits on the product of the production cross
section $sigmaleft(e^+e^- to h^prime chi_1 chi_2right)$, and the product
of branching fractions $mathcal{B}left(chi_2tochi_1 e^+
e^-right)timesmathcal{B}left(h^primeto x^+x^-right)$, where $x^+x^-$
indicates $mu^+mu^-, pi^+pi^-$, or $K^+K^-$, as functions of $h^{prime}$
mass and lifetime at the level of $10^{-1},mbox{fb}$. We set model-dependent
upper limits on the dark Higgs mixing angle at the level of $10^{-5}$ and on
the dark photon kinetic mixing parameter at the level of $10^{-3}$. This is the
first search for dark Higgs bosons in association with inelastic dark matter.
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