An approach to study interactions of antineutrons with CsI at a $J/\psi$ factory

Cesium Iodide (CsI) crystals are widely used in high-energy physics for their scintillation properties that enable detection of charged and neutral particles via direct and indirect ionization and form the basis of electromagnetic calorimeters. However, knowledge of antineutron interactions with CsI is limited due to the difficulty of obtaining sources of antineutron of sufficient intensity and energy definition. As antineutron are abundantly produced by many processes it would be particularly useful to improve understanding of the interactions of antineutrons with CsI crystals. We propose to use the decay $J/\psi\to p\pi^-\bar{n}$ at the BEPCII $J/\psi$ factory as a source of antineutrons using the BESIII detector with a CsI target added between the beam pipe and the detector. The BESIII Monte Carlo simulation with varying thicknesses of CsI target is used to validate the approach and optimize the target thickness. Selecting $p\pi^-$ charged particle tracks from the Monte Carlo we obtain clean antineutron samples with well defined momentum and direction. The selection efficiency, momentum and angular resolutions, as well as the interaction probability between antineutron and the CsI target are estimated. As the CsI thickness is increased more antineutron CsI interactions are obtained,however the quality of the $p\pi^-$ selection is degraded. The Monte Carlo study yields an optimum thickness that balances these effects. This approach can be applied to similar experiments with other types of target materials to measure baryons such as liquid hydrogen/deuterium and $\Lambda/\Xi$ hyperons.