Observation of $\bar{\Lambda}p\to K^{+}\pi^{+}\pi^{-}\pi^{0}$ and $\bar{\Lambda}p\to K^{+}\pi^{+}\pi^{-}2\pi^{0}$

TL;DR

This paper reports the first observation of specific antihyperon-nucleon annihilation processes using a large dataset from BESIII, measuring cross sections and identifying resonance contributions to enhance understanding of these interactions.

Contribution

The study provides the first measurements of cross sections for $ar{ ext{Lambda}} p$ annihilation into multi-pion and kaon final states, including evidence for the $K^{*}(892)^+$ resonance.

Findings

First observation of $ar{ ext{Lambda}} p o K^+ ext{pion} ext{final states}$

Measured cross sections: 8.5 mb and 7.9 mb for two channels

Evidence for $K^{*}(892)^+$ resonance in the $K^+ ext{pi}^0$ spectrum

Abstract

Using $(10087 \pm 44) \times 10^6$ $J/\psi$ events collected with the BESIII detector at a center-of-mass energy of $\sqrt{s}=3.097$ GeV, the antihyperon-nucleon annihilation processes $\bar{\Lambda} p \to K^+ \pi^+ \pi^- + k\pi^0$ ($k=1,2,3$) are studied at an incident $\bar{\Lambda}$ momentum of approximately 1.074 GeV/$c$. The reactions $\bar{\Lambda} p \to K^+ \pi^+ \pi^- \pi^0$ and $\bar{\Lambda} p \to K^+ \pi^+ \pi^- 2\pi^0$ are observed for the first time, with corresponding cross sections $\sigma_{\bar{\Lambda} p \to K^+ \pi^+ \pi^- \pi^0} = 8.5^{+1.2}_{-1.1} (\rm{stat.}) \pm 0.4 (\rm {syst.})$ mb and $\sigma_{\bar{\Lambda} p \to K^+ \pi^+ \pi^- 2\pi^0} = 7.9^{+1.9}_{-1.7} \pm 0.4$ mb. No significant signal is found for $\bar{\Lambda} p \to K^+ \pi^+ \pi^- 3\pi^0$, and an upper limit of 7.2 mb is set at a 90\% confidence level. An evidence for the $K^{*}(892)^+$ resonance is seen in the $K^+\pi^0$ invariant mass spectrum $M_{K^+\pi^0}$ for $k=1$, and the corresponding cross section for $\bar{\Lambda} p \to K^{*}(892)^+ \pi^+ \pi^-$ is measured to be $\sigma_{\bar{\Lambda} p \to K^{*}(892)^+ \pi^+ \pi^-} = 12.5^{+3.8}_{-3.4} \pm 1.2$ mb. Owing to the limited statistics, possible interference effects are not considered. These findings offer crucial input to deepen our understanding of the antihyperon-nucleon interactions.