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

Abstract

We report a partial-wave analysis of new data on the double-polarization variable $E$ for the reactions $γp\to π^+ n$ and $γp\to π^0 p$ 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 $Δ(2200)7/2^-$. This is the lowest-mass $Δ^*$ resonance with spin-parity $J^P=7/2^-$. Its mass is significantly higher than the mass of its parity partner $Δ(1950)7/2^+$ which is the lowest-mass $Δ^*$ 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.

5 pages, 3 figures; Physics Letters B in press