Search for sub-GeV dark particles in $\hat{I}\cdot \to \ddot{I}{€}^0+\mathrm{invisible}$ decay

Abstract

Using (10087$\pm$44)$\times$10${}^6$ $J/\ddot{I}ˆ$ events collected with the BESIII detector at the BEPCII collider at the center-of-mass energy of $\sqrt{s}=3.097\mathrm{GeV}$, we report the first search for $\hat{I}\cdot \to \ddot{I}{€}^{0}S\to \ddot{I}{€}^0\ddot{I}‡\bar{\ddot{I}}‡$ with $S$ denotes an on-shell dark scalar boson and $\ddot{I}‡$ an invisible dark matter particle. No significant signals are observed with $S$ mass ranging from 0 to 400 $\mathrm{MeV}/{\mathrm{c}}^2$. The upper limits on the branching fractions and the new physics coupling strengths between $S$ and quarks are set to be $(1.8\sim 5.5)\times 10^{-5}$ and $(1.3\sim 3.2)\times 10^{-5}$ at the 90% confidence level, respectively. The constraints on the dark-matter-nucleon scattering cross section is improved by approximately 5 orders of magnitude over previous dark-matter-nucleon scattering experiments, providing unique insights into sub-GeV dark matter.

13 pages, 7 figures