  Sub-MeV cold dark-matter particles are unable to produce electronic recoil in
conventional dark-matter direct detection experiments such as XENONnT and
LUX-ZEPLIN above the detector threshold. The mechanism of boosted dark matter
comes into picture to constrain the parameter space of such low mass dark
matter from direct detection experiments. We consider the effect of the leading
components of cosmic rays to boost the cold dark matter, which results in
significant improvements on the exclusion limits compared to the existing ones.
To present concrete study results, we choose to work on models consisting of a
dark-matter particle $\chi$ with an additional $U(1)'$ gauge symmetry including
the secluded dark photon, $U(1)_{B-L}$, and $U(1)_{L_e-L_\mu}$. We find that
the energy dependence of the scattering cross section plays a crucial role in
improving the constraints. In addition, we systematically estimate the Earth
shielding effect on boosted dark matter in losing energy while traveling to the
underground detector through the Earth.
