Sensitivity of Hongmeng 21cm experiment on scattering dark matter

Scattering between dark matter and baryon can cool intergalactic medium temperature and deepen the 21cm signal. Such interactions have been proposed to explain the unusually deep 21cm absorption signal reported by EDGES in 2018. This paper explores the potential to detect dark matter - baryon scattering with the Hongmeng project, an upcoming lunar orbiting satellite experiment dedicated to measuring global 21cm signal between redshifts $11-46$. We self-consistently forward-model the simulated sky temperature data, jointly varying both the astrophysical and foreground models. We show that even with a very conservative observational strategy in which the experiment only takes data when both the Earth and the Sun are shielded by the Moon, Hongmeng can tighten the current constraints on dark matter - baryon scattering cross-section $\sigma_0$ by a factor of 21 after the full mission which lasts for five years. The prospective upper limit on $\sigma_0$ can reach $4 \times 10^{-43} {\rm cm^2}$ for dark matter masses between 0.1 MeV and 0.4 GeV. Even after only one month of observation, a factor of 3 improvement relative to current $\sigma_0$ limits can be expected.