发表机构
Shanghai Jiao Tong University（上海交通大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究提出利用横向τ自旋关联在未来的Z工厂探测CP破坏，通过避免手征抑制并增强响应，显著提高弱电偶极矩的测量精度，比现有实验改进多个数量级。
AI 中文摘要
在$Z$极点处的τ自旋关联探测CP破坏，其灵敏度强烈依赖于自旋投影。对于固定的$Z$样本，横向矩避免了纵向和三重乘积可观测量中的手征抑制，将响应增强因子$m_Z/2m_\tau=26$。两个横向矩还选择轴向τ电荷，获得$|a_\tau/v_\tau|=13.5$的增益；符号加权的法向矩的响应是三重乘积的$521$倍。这两个横向矩给出的单参数不确定度不超过我们计算的Cramér-Rao下界的$14\\%$，用于独立的单π测量，接近该分析中的最佳精度。使用$5\\%$离峰亮度的五矩拟合，在FCC-ee（CEPC）上对$\operatorname{Re}\widetilde{d}_\tau^W$和$\operatorname{Im}\widetilde{d}_\tau^W$的统计不确定度分别为$4.5 (5.5)\times10^{-7}$和$2.7 (3.2)\times10^{-6}$，比ALEPH提高三个数量级。电磁偶极矩不确定度在$\operatorname{Re}\widetilde{d}_\tau^\gamma$上为$9.6 (12)\times10^{-6}$，比Belle超出两个数量级。这些预测假设理想的角重建和扫描中恒定的形状因子。
英文摘要
Tau spin correlations at the $Z$ pole probe CP violation with a sensitivity that depends strongly on the spin projection. For a fixed $Z$ sample, transverse moments avoid the chirality suppression of longitudinal and triple-product observables, enhancing the response by a factor $m_Z/2m_τ=26$. Two transverse moments also select the axial tau charge, gaining $|a_τ/v_τ|=13.5$; the sign-weighted normal moment has a response $521$ times that of the triple product. These two transverse moments give single-parameter uncertainties no more than $14\%$ above our calculated Cramer-Rao bound for independent single-pion measurements, approaching the best precision within this analysis. A five-moment fit with $5\%$ off-peak luminosity yields statistical uncertainties of $4.5 (5.5)\times10^{-7}$ and $2.7 (3.2)\times10^{-6}$ on $\operatorname{Re}\widetilde{d}_τ^W$ and $\operatorname{Im}\widetilde{d}_τ^W$, respectively, at FCC-ee (CEPC), improving on ALEPH by three orders of magnitude. The electromagnetic-dipole uncertainty is $9.6 (12)\times10^{-6}$ on $\operatorname{Re}\widetilde{d}_τ^γ$, two orders beyond Belle. These projections assume ideal angular reconstruction and constant form factors across the scan.
Comments8 pages, 2 figures, 1 table
