Measurement of inelastic scattering $\Lambda (\overline{\Lambda })+p\to {\Sigma }^0({\overline{\Sigma }}^0)+p$ via $e^{+}{e}^{-}\to J/\psi \to \Lambda \overline{\Lambda }$

Abstract

Using a sample of $(10087\pm 44)\times 10^6$ $J/\psi$ events collected with the BESIII detector, we investigate the inelastic scattering processes $\Lambda +p\to {\Sigma }^0+p$ and $\overline{\Lambda }+p\to {\overline{\Sigma }}^0+p$, exploiting hyperons from $J/\psi \to \Lambda \overline{\Lambda }$ decays as an effective beam and the beam-pipe materials as targets. The processes $\Lambda +{}^9\mathrm{Be}\to {\Sigma }^0+p+{}^8\mathrm{Li}$ and $\overline{\Lambda }+{}^9\mathrm{Be}\to {\overline{\Sigma }}^0+p+{}^8\mathrm{Li}$ are measured at a hyperon momentum of $1.074\mathrm{GeV}/c$, with cross sections of $(10.1\pm 1.4_{\mathrm{stat}}\pm 0.7_{\mathrm{syst}})$ mb and $(1.7\pm 0.6_{\mathrm{stat}}\pm 0.4_{\mathrm{syst}})$ mb, respectively. Under the assumption of surface-dominated hyperon-nucleus scattering, these measurements are used to extract the corresponding proton-target cross sections. Independently, direct measurements using the hydrogen component of the beam-pipe oil yield $(3.2\pm 1.1_{\mathrm{stat}}\pm 0.5_{\mathrm{syst}})$ mb for $\Lambda +p\to {\Sigma }^0+p$ and $(1.5\pm 0.5_{\mathrm{stat}}\pm 0.1_{\mathrm{syst}})$ mb for $\overline{\Lambda }+p\to {\overline{\Sigma }}^0+p$, consistent with the indirect determinations. The combined cross sections are $(4.7\pm 0.7)$ mb and $(1.1\pm 0.3)$ mb, respectively. The $\overline{\Lambda }+p\to {\overline{\Sigma }}^0+p$ signal constitutes the first evidence for anti-hyperon inelastic scattering with baryonic final states, with a significance of $3.1\sigma$. The pronounced difference between the $\Lambda p$ and $\overline{\Lambda }p$ inelastic scattering cross sections provides new experimental constraints on hyperon-nucleon and anti-hyperon-nucleon interactions.