Proposal for Studying $N^*$ Resonances with $\bar{p}p \to \bar{p}n \pi^+ $ Reaction

TL;DR

This paper theoretically investigates the $ar{p}p o ar{p}n \pi^+$ reaction at 1-4 GeV to identify the dominant contributions and its potential for studying $N^*$ resonances, especially the Roper resonance, in upcoming experiments.

Contribution

It provides a detailed theoretical analysis of the reaction mechanism, highlighting the dominance of the Roper resonance at certain energies and proposing this reaction as a promising probe for $N^*$ states.

Findings

Roper resonance $N^*_{(1440)}$ dominates at 1.5 GeV.

Reaction is suitable for studying $N^*$ and missing resonances.

Reaction can be explored in the upcoming $ar{P}$ANDA$ experiment.

Abstract

A theoretical study of $\bar{p}p \to \bar{p}n \pi^+ $ reaction for anti-proton beam energy from 1 to 4 GeV is made by including contributions from various known $N^*$ and $\Delta^*$ resonances. It is found that for the beam energy around 1.5 GeV, the contribution of the Roper resonance $N^*_{(1440)}$ produced by the t-channel $\sigma$ exchange dominates over all other contributions. Since such reaction can be studied in the forthcoming $\bar{P}$ANDA experiment at Facility of Antiproton and Ion Research (FAIR), the reaction will be realistically the cleanest place for studying the properties of the Roper resonance and the best place for looking for other "missing" $N^*$ resonances with large coupling to $N\sigma$.