Cross Section Measurements of $\bar{n}p \rightarrow K^{+}K^{-}π^{+}(π^{0})$ via Antineutrons Produced by $J/ψ\to p π^{-} \bar{n}$ Decays

Abstract

Based on a novel method for producing antineutrons via $J/ψ$ decays, we report a study of $\bar{n}p$ inelastic scattering into final states containing kaons. The analysis uses $(10087\pm44)\times 10^6$ $J/ψ$ events collected at the BESIII detector operating at the BEPCII storage ring. Antineutrons are produced via $J/ψ\to p π^{-} \bar{n}$ decays and tagged by the detected protons and pions, resulting in antineutron momenta ranging from 0 to 1174~MeV/$c$, while target protons are provided by the hydrogen in the beam-pipe material. The cross sections of the reactions $\bar{n}p \rightarrow K^{+}K^{-}π^{+}$ and $\bar{n}p \rightarrow K^{+}K^{-}π^{+}π^{0}$ are measured to be $0.53^{+0.15}_{-0.12} \pm 0.08$~mb and $1.09^{+0.36}_{-0.30} \pm 0.31$~mb respectively, where the first uncertainties are statistical and the second systematic. Due to limited statistics, the intermediate states in these processes are not investigated. The observation of clean antineutron-proton scattering events indicates the potential of this approach for future investigations of antineutron-proton interactions.

Figures (5)

• Figure 1: The distribution of $RM(p\pi^-)$. The dots with error bars are data, the blue solid line is the total fit, the red dashed line is the signal shape, and the green dashed line is the background shape.
• Figure 2: The momentum distribution of tagged antineutrons when $RM(p\pi^-)\in [0.92,0.96]\mathrm{\ Ge V}/c^2 {\textrm{Ge V}/$c^2$}$.
• Figure 3: The distribution of $R_{xy}$. A clear peak is observed, which is consistent with the beam pipe radius [3.15, 3.37] cm.
• Figure 4: The distributions of $\Delta E$ for $\bar{n}p \rightarrow K^{+}K^{-}\pi^{+}$ (left) and $\bar{n}p \rightarrow K^{+}K^{-}\pi^{+}\pi^0$ (right). The dots with error bars are data, the blue solid lines are the total fits, the red dashed lines are the signal shapes, and the green dashed lines are the background shapes.
• Figure 5: The distributions of the invariant masses of $K^+K^-$ for $\bar{n}p \rightarrow K^{+}K^{-}\pi^{+}$ (left) and $\bar{n}p \rightarrow K^{+}K^{-}\pi^{+}\pi^0$ (right) in data.