First measurement of $\hat{I}{\pounds }^{+}n\to \hat{I}›p$ and $\hat{I}{\pounds }^{+}n\to \hat{I}{\pounds }^{0}p$ cross sections via $\hat{I}{\pounds }^{+}$-nucleus scattering at an electron-positron collider

Abstract

Using $(1.0087\pm 0.0044)\times 10^{10}$ $J/\ddot{I}ˆ$ events collected with the BESIII detector at the BEPCII storage ring, the reactions $\hat{I}{\pounds }^{+}n\to \hat{I}›p$ and $\hat{I}{\pounds }^{+}n\to \hat{I}{\pounds }^{0}p$ are studied, where the $\hat{I}{\pounds }^{+}$ baryon is produced in the process $J/\ddot{I}ˆ\to \hat{I}{\pounds }^{+}\bar{\hat{I}}{\pounds }^{-}$ and the neutron is a component of the ${}^9\mathrm{Be}$, ${}^{12}\mathrm{C}$ and ${}^{197}\mathrm{Au}$ nuclei in the beam pipe. Clear signals of these two reactions are observed for the first time. Their cross sections are measured to be $\ddot{I}ƒ(\hat{I}{\pounds }^{+}+{}^9\mathrm{Be}\to \hat{I}›+p+X)=(45.2\pm 12.1_{\mathrm{stat}}\pm 7.2_{\mathrm{sys}})$ mb and $\ddot{I}ƒ(\hat{I}{\pounds }^{+}+{}^9\mathrm{Be}\to \hat{I}{\pounds }^0+p+X)=(29.8\pm 9.7_{\mathrm{stat}}\pm 6.9_{\mathrm{sys}})$ mb for a $\hat{I}{\pounds }^{+}$ average momentum of $0.992$ GeV/$c$, within a range of $\pm 0.015$ GeV/$c$, where $X$ represents the residual nucleus. This is the first study of $\hat{I}{\pounds }^{+}$-nucleon scattering at an electron-positron collider.

9 pages, 2 figures