Observation of Λ ¯ p → K + π + π − π 0 and Λ ¯ p → K + π + π − 2 π 0

Using (10 087±44)×10⁶ J/ψ events collected with the BESIII detector at a center-of-mass energy of sqrt[s]=3.097 GeV, the antihyperon-nucleon annihilation processes Λ[over ¯]p→K⁺π⁺π⁻+kπ⁰ (k=1, 2, 3) are studied at an incident Λ[over ¯] momentum of approximately 1.074 GeV/c. The reactions Λ[over ¯]p→K⁺π⁺π⁻π⁰ and Λ[over ¯]p→K⁺π⁺π⁻2π⁰ are observed for the first time, with corresponding cross sections σ_{Λ[over ¯]p→K⁺π⁺π⁻π⁰}=8.5-1.1+1.2(stat)±0.4(syst) mb and σ_{Λ[over ¯]p→K⁺π⁺π⁻2π⁰}=7.9-1.7+1.9±0.4 mb. No significant signal is found for Λ[over ¯]p→K⁺π⁺π⁻3π⁰, and an upper limit of 7.2 mb is set at a 90% confidence level. Evidence for the K*(892)⁺ resonance is seen in the K⁺π⁰ invariant mass spectrum M_{K⁺π⁰} for k=1, and the corresponding cross section for Λ[over ¯]p→K*(892)⁺π⁺π⁻ is measured to be σ_{Λ[over ¯]p→K*(892)⁺π⁺π⁻}=12.5-3.4+3.8±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.