Evidence for $\Delta (2200)7/2^{-}$ 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 $\gamma p\to {\pi }^{+}n$ 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 ${\Delta }^{\ast }$ 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 ${\Delta }^{\ast }$ 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.

Comments: 5 pages, 3 figures; Physics Letters B in press