First study of antihyperon-nucleon scattering $\bar{\hat{I}}›p\to \bar{\hat{I}}›p$ and measurement of $\hat{I}›p\to \hat{I}›p$ cross section

Abstract

Using $(10.087\pm 0.044)\times 10^9$ $J/\ddot{I}ˆ$ events collected with the BESIII detector at the BEPCII storage ring, the processes $\hat{I}›p\to \hat{I}›p$ and $\bar{\hat{I}}›p\to \bar{\hat{I}}›p$ are studied, where the $\hat{I}›/\bar{\hat{I}}›$ baryons are produced in the process $J/\ddot{I}ˆ\to \hat{I}›\bar{\hat{I}}›$ and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in $-0.9\le \cos \hat{\mathrm{I}}{¸}_{\hat{\mathrm{I}}›/\overline{\hat{\mathrm{I}}}›}\le 0.9$ are measured to be $\ddot{I}ƒ(\hat{I}›p\to \hat{I}›p)=(12.2\pm 1.6_{\mathrm{stat}}\pm 1.1_{\mathrm{sys}})$ mb and $\ddot{I}ƒ(\bar{\hat{I}}›p\to \bar{\hat{I}}›p)=(17.5\pm 2.1_{\mathrm{stat}}\pm 1.6_{\mathrm{sys}})$ mb at the $\hat{I}›/\bar{\hat{I}}›$ momentum of $1.074$ GeV/$c$ within a range of $\pm 0.017$ GeV/$c$, where the $\hat{I}{¸}_{\hat{I}›/\bar{\hat{I}}›}$ are the scattering angles of the $\hat{I}›/\bar{\hat{I}}›$ in the $\hat{I}›p/\bar{\hat{I}}›p$ rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for $\hat{I}›p\to \hat{I}›p$, and a strong forward peak for $\bar{\hat{I}}›p\to \bar{\hat{I}}›p$. We present an approach to extract the total elastic cross sections by extrapolation. The study of $\bar{\hat{I}}›p\to \bar{\hat{I}}›p$ represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction.

9 pages, 5 figures