Kavli Affiliate: Jia Liu
| First 5 Authors: Mingxuan Du, Jia Liu, Xiao-Ping Wang, Tianhao Wu,
| Summary:
We investigate the enhancement of dark sector particle production within the
scattering dominant regime. These particles typically exhibit a slight mixing
with Standard Model particles through various portals, allowing for their
generation through in-medium oscillation from Standard Model particle sources.
Our analysis reveals that in the scattering dominance regime, with a
significantly smaller scattering mean free path $lambda_{rm sca}$ compared to
the absorption mean free path $lambda_{rm abs}$, the nonresonant production
of sterile states can experience an enhancement by a factor of $lambda_{rm
abs}/lambda_{rm sca}$. This phenomenon is demonstrated within the context of
kinetic mixing dark photon production at a reactor, precisely satisfying this
condition. By incorporating this collisional enhancement, we find that the
current sensitivity to the mixing parameter $epsilon$ for dark photons in the
TEXONO experiment can be significantly improved across a range spanning from
tens of eV to MeV. This advancement establishes the most stringent laboratory
constraint within this mass spectrum for the dark photon. Sterile neutrino
production, however, does not exhibit such enhancement, either due to the
failure to meet the scattering dominance criterion or the neutrino damping in
resonant production.
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