First measurement of $\Sigma^{+}n\rightarrow\Lambda p$ and $\Sigma^{+}n\rightarrow\Sigma^{0}p$ cross sections via $\Sigma^+$-nucleus scattering at an electron-positron collider

TL;DR

This paper reports the first measurement of specific $oldsymbol{ ext{Sigma}^+ n}$ scattering cross sections at an electron-positron collider, using $J/ ext{psi}$ decays to produce $ ext{Sigma}^+$ baryons and analyzing their interactions with nuclei.

Contribution

It provides the first experimental measurements of $ ext{Sigma}^+ n$ scattering cross sections at an electron-positron collider, expanding understanding of hyperon-nucleon interactions.

Findings

Measured cross sections for $ ext{Sigma}^+ + ^9 ext{Be} ightarrow ext{Lambda} + p + X$ and $ ext{Sigma}^+ + ^9 ext{Be} ightarrow ext{Sigma}^0 + p + X$.

First observation of these reactions in this experimental setup.

Cross sections are approximately 45.2 mb and 29.8 mb with statistical and systematic uncertainties.

Abstract

Using $(1.0087\pm0.0044)\times10^{10}$ $J/\psi$ events collected with the BESIII detector at the BEPCII storage ring, the reactions $\Sigma^{+}n\rightarrow\Lambda p$ and $\Sigma^{+}n\rightarrow\Sigma^{0}p$ are studied, where the $\Sigma^{+}$ baryon is produced in the process $J/\psi\rightarrow\Sigma^{+}\bar{\Sigma}^-$ and the neutron is a component of the $^9\rm{Be}$, $^{12}\rm{C}$ and $^{197}\rm{Au}$ nuclei in the beam pipe. Clear signals of these two reactions are observed for the first time. Their cross sections are measured to be $\sigma(\Sigma^{+}+{^9\rm{Be}}\rightarrow\Lambda+p+X)=(45.2\pm12.1_{\rm{stat}}\pm7.2_{\rm{sys}})$ mb and $\sigma(\Sigma^{+}+{^9\rm{Be}}\rightarrow\Sigma^{0}+p+X)=(29.8\pm9.7_{\rm{stat}}\pm6.9_{\rm{sys}})$ mb for a $\Sigma^{+}$ average momentum of $0.992$ GeV/$c$, within a range of $\pm0.015$ GeV/$c$, where $X$ represents the residual nucleus. This is the first study of $\Sigma^{+}$-nucleon scattering at an electron-positron collider.