# Unexpected neutron/proton ratio and isospin effect in low-energy antiproton induced reactions

## TL;DR

This study investigates neutron/proton ratios in low-energy antiproton-nucleus collisions, revealing isospin effects influenced by symmetry energy and pion-nucleon interactions, with implications for nuclear matter properties.

## Contribution

First application of the Lanzhou quantum molecular dynamics model to analyze neutron/proton ratios in antiproton-induced reactions, highlighting isospin effects and constraining symmetry energy.

## Key findings

- Neutron/proton ratio differs from pion and proton induced reactions due to isospin effects.
- Pion-nucleon interactions, especially π−-neutron collisions, enhance neutron emission.
- A soft symmetry energy with γ_s=0.5 is consistent with the data.

## Abstract

The inclusive spectra of preequilibrium nucleons produced in low-energy antiproton-nucleus collisions are thoroughly investigated within the framework of the Lanzhou quantum molecular dynamics model for the first time. All possible reaction channels such as elastic scattering, annihilation, charge exchange and inelastic scattering in antibaryon-baryon, baryon-baryon and meson-baryon collisions have been included in the transport model. The unexpected neutron/proton ratio in comparison to the pion and proton induced reactions is caused from the isospin effects of pion-nucleon collisions and the density dependence of symmetry energy. It is found that the $\pi^{-}$-neutron collisions enhance the neutron emission in the antiproton annihilation in a nucleus. Different to heavy-ion collisions, the isospin effects are pronounced at the low kinetic energies. A soft symmetry energy with the stiffness of $\gamma_{s}=$0.5 at subsaturation densities is constrained from the available data of the neutron/proton spectra.