Phenomenological study on the $\bar p N\to \bar NN\pi\pi$ reactions

TL;DR

This study analyzes antiproton-nucleon reactions producing two pions using an effective Lagrangian approach, highlighting the dominant roles of specific resonances near threshold energies and suggesting experimental opportunities at PANDA/FAIR.

Contribution

It extends previous proton-nucleon reaction studies to antiproton-nucleon reactions, identifying key resonance contributions and their energy-dependent behaviors.

Findings

$N^*(1440)$ resonance dominates near threshold energies.

Double-$ riangle$ and $ riangle(1600)$ resonances are significant at higher energies.

Antinucleon-nucleon reactions provide complementary insights to nucleon-nucleon reactions.

Abstract

We extend our recent phenomenological study of $pN \to NN\pi\pi$ reactions to the $\bar{p}N \to \bar{N}N\pi\pi$ reactions for anti-proton beam momenta up to 3.0 GeV within an effective Lagrangian approach. The contribution of $N^*(1440)$ with its $N\sigma$ decay mode is found to be dominant at the energies close to threshold for $\bar NN\pi^+\pi^-$ and $\bar NN\pi^0\pi^0$ channels. At higher energies or for $p\bar n\pi^-\pi^-$ and $\bar NN\pi^\pm\pi^0$ channels where $N^*(1440)\to N\sigma$ mode cannot contribute, large contributions from double-$\Delta$, $\Delta(1600) \to N^*(1440)\pi$, $\Delta(1600) \to \Delta\pi$ and $\Delta(1620) \to \Delta\pi$ are found. In the near-threshold region, sizeable contributions from $\Delta \to \Delta\pi$, $\Delta \to N\pi$, $N \to \Delta\pi$ and nucleon pole are also indicated. Although these results are similar to those for $pN\to NN\pi\pi$ reactions, the antinucleon-nucleon collisions are shown to be complementary to the nucleon-nucleon collisions and may even have advantages in some aspects. The PANDA/FAIR experiment is suggested to be an excellent place for studying the properties of relevant $N^*$ and $\Delta^*$ resonances.