发表机构
Nanjing Normal University; University of Chinese Academy of Sciences; Institute of High Energy Physics, Chinese Academy of Sciences（南京师范大学; 中国科学院大学; 中国科学院高能物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
BESIII合作组分析ψ(2S)→p$\bar{p}$η的不变质量谱，发现1.564GeV处的类尖点结构与三角奇异性预言位置吻合，纳入该效应后拟合显著性达3.8σ，为三角奇异性提供首个实验证据。
AI 中文摘要
三角奇异性由朗道于1959年预言，是强子再散射圈产生的纯运动学增强效应。尽管其被认为在多种反常衰变过程和奇特强子候选体中起作用，六十多年来却始终缺乏直接实验证实。我们分析了BESIII合作组测量的ψ(2S)→p$\bar{p}$η过程中的pη/$\bar{p}$η不变质量谱，数据在N(1535)区域的1.564GeV附近呈现清晰的类尖点结构，与三角奇异性预言的运动学位置精确吻合。在拟合中纳入三角奇异性圈后，对数据的描述大幅改善，χ²/自由度从1.22降至0.90，对应三角奇异性贡献的显著性约为3.8σ。观测到的 excess 与预言的运动学位置精确对齐，为三角奇异性效应提供了首个令人信服的证据。
英文摘要
Triangle singularities, predicted by Landau in 1959, are purely kinematic enhancements arising from hadronic rescattering loops. Despite their proposed role in various anomalous decay processes and exotic hadron candidates, a direct experimental confirmation has remained elusive for more than six decades. We analyze the $pη/\bar{p}η$ invariant mass spectrum in $ψ(2S) \to p\bar{p}η$ measured by the BESIII Collaboration. The data exhibit a clear cusp-like structure around 1.564~GeV in the $N(1535)$ region, in precise agreement with the kinematic position predicted for the triangle singularity. Including the triangle singularity loop in the fit substantially improves the description of the data, with $χ^2/\mathrm{d.o.f.}$ decreasing from 1.22 to 0.90, corresponding to a significance of $\sim 3.8σ$ for the triangle singularity contribution. The precise alignment of the observed excess with the predicted kinematic position provides the first compelling evidence for the triangle singularity effect.
