Evidence for $\Delta(2200)7/2^-$ from photoproduction and consequence for chiral-symmetry restoration at high mass

TL;DR

This study provides evidence for the $ ext{Δ}(2200)7/2^-$ resonance through photoproduction data analysis, challenging the idea that chiral symmetry restoration leads to degeneracy between parity partner resonances at high mass.

Contribution

The paper identifies the $ ext{Δ}(2200)7/2^-$ resonance and compares its mass to its parity partner, providing new insights into baryon resonance structure and chiral symmetry restoration.

Findings

Evidence for the $ ext{Δ}(2200)7/2^-$ resonance was found.

The mass difference between $ ext{Δ}(2200)7/2^-$ and $ ext{Δ}(1950)7/2^+$ contradicts chiral symmetry restoration predictions.

Abstract

We report a partial-wave analysis of new data on the double-polarization variable $E$ for the reactions $\gamma p\to \pi^+ n$ and $\gamma p\to \pi^0 p$ and of further data published earlier. The analysis within the Bonn-Gatchina (BnGa) formalism reveals evidence for a poorly known baryon resonance, the one-star $\Delta(2200)7/2^-$. This is the lowest-mass $\Delta^*$ resonance with spin-parity $J^P=7/2^-$. Its mass is significantly higher than the mass of its parity partner $\Delta(1950)7/2^+$ which is the lowest-mass $\Delta^*$ resonance with spin-parity $J^P=7/2^+$. It has been suggested that chiral symmetry might be restored in the high-mass region of hadron excitations, and that these two resonances should be degenerate in mass. Our findings are in conflict with this prediction.