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 antineutron sources in sufficient intensity and wide energy range. As antineutron are abundantly produced by many physics process, it would be particularly useful to improve understanding of the interactions of antineutrons with CsI crystals.

We propose to use decay of \(J/\psi \rightarrow p\pi ^-\bar{n}\) $J/\psi \to p{\pi }^{-}\overline{n}$ at a \(J/\psi \) $J/\psi$ factory as a source of antineutrons and a CsI target added between the beam pipe and the detector to study such interactions. We use Monte Carlo simulation at the BESIII experiment as a proof of the concept. The simulation with varying thicknesses of CsI target is performed to validate the approach and optimize the target thickness.

Selecting charged particle tracks (p and \(\pi ^-\) ${\pi }^{-}$ ) from the Monte Carlo sample, 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 \(p\pi ^-\) $p{\pi }^{-}$ part 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 such as liquid hydrogen/deuterium and other baryons such as \(\Lambda \) $\mathrm{\Lambda }$ and \(\Xi \) $\mathrm{\Xi }$ .