First measurement of Σ⁺n→Λ p and Σ⁺n→Σ⁰p cross-sections via Σ⁺-nucleus scattering at an electron-positron collider

Using (1.0087±0.0044)×10¹⁰ J/ψ events collected with the BESIII detector at the BEPCII storage ring, the reactions Σ⁺n→Λ p and Σ⁺n→Σ⁰p are studied, where the Σ⁺ baryon is produced in the process J/ψ→Σ⁺Σ̄⁻ and the neutron is a component of the ⁹Be, ¹²C and ¹⁹⁷Au nuclei in the beam pipe. Clear signals of these two reactions are observed for the first time. Their cross-sections are measured to be σ(Σ⁺+⁹Be→Λ+p+⁸Be)=(45.2±12.1ₛₜₐₜ±7.2sys) mb and σ(Σ⁺+⁹Be→Σ⁰+p+⁸Be)=(29.8±9.7ₛₜₐₜ±6.9sys) mb for a Σ⁺ average momentum of $0.992$ GeV/c, within a range of ±0.015 GeV/c. This is the first study of Σ⁺-nucleon scattering at an electron-positron collider.