The NA48/2 experiment at CERN reports the first observation of the [Formula: see text] decay from an exposure of [Formula: see text] charged kaon decays recorded in 2003–2004. A sample of 4919 candidates with 4.9% background contamination allows the determination of the branching ratio in the full kinematic region. The study of the kinematic space shows evidence for a structure-dependent contribution in agreement with predictions based on chiral perturbation theory. Several [Formula: see text]- and [Formula: see text]-violating asymmetries are also evaluated. The most precise measurement of the charged kaon semi-leptonic form factors obtained by NA48/2 with 4.4 million [Formula: see text] and 2.3 million [Formula: see text] events collected in 2004 will also be presented.

中文翻译：

---

来自 NA48/2 实验的罕见 kaon 衰变的最新结果@CERN

欧洲核子研究中心的 NA48/2 实验报告了对 2003-2004 年记录的 [公式：见文本] 带电 kaon 衰变暴露造成的 [公式：见文本] 衰变的首次观察。具有 4.9% 背景污染的 4919 个候选样本允许确定整个运动学区域中的分支比。对运动学空间的研究显示了与基于手性微扰理论的预测一致的结构相关贡献的证据。还评估了几个违反 [公式：参见文本] 和 [公式：参见文本] 的不对称性。NA48/2 在 2004 年收集到的 440 万个 [公式：见文本] 和 230 万个 [公式：见文本] 事件获得的带电 kaon 半轻子形式因子的最精确测量也将呈现。