发表机构
University of California Santa Cruz; Santa Cruz Institute for Particle Physics; ELTE Eötvös Loránd University（加州大学圣克鲁兹分校; 圣克鲁兹粒子物理研究所; 罗兰大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
研究极化$\Lambda_b$重子稀有衰变$\Lambda_b\to\Lambda(\to p\pi^-)\nu\bar{\nu}$的角观测量，发现五个独立观测量可探测正交Wilson系数组合及CP破坏相位，对FCC-ee新物理灵敏度作出评估。
AI 中文摘要
我们研究了在$Z$极点处产生的极化$\Lambda_b$重子的稀有衰变$\Lambda_b \rightarrow \Lambda(\rightarrow p\pi^-)\nu\bar{\nu}$。我们发现微分衰变分布由五个独立的角观测量表征，其中四个需要初始$\Lambda_b$极化。虽然介子$b \rightarrow s \nu \bar{\nu}$衰变（$B \rightarrow K^{(*)} \nu \bar{\nu}$，$B_s \rightarrow \phi \nu \bar{\nu}$）中的标准观测量仅探测短距离Wilson系数的两个组合$|C_L + C_R|$和$|C_L - C_R|$，但$\Lambda_b \rightarrow \Lambda(\rightarrow p\pi^-)\nu\bar{\nu}$中的角观测量能够提供对正交组合$|C_R|^2 - |C_L|^2$和$\text{Im}(C_L C_R^*)$的访问。特别地，我们识别出一个$T$-奇CP不对称量$A_5$，它直接探测短距离有效哈密顿量中的CP破坏相位。我们使用格点QCD形状因子给出了标准模型对分支比和所有角观测量的预测，并评估了FCC-ee上投影的新物理灵敏度。我们的结果表明，重子角观测量对于解决参数简并以及完全表征$b \rightarrow s \nu \bar{\nu}$跃迁中可能的新物理的手征和CP结构至关重要。
英文摘要
We study the rare decay $Λ_b \rightarrow Λ(\rightarrow pπ^-)ν\barν$ of polarized $Λ_b$ baryons produced at the $Z$ pole. We find that the differential decay distribution is characterized by five independent angular observables, four of which require initial $Λ_b$ polarization. While standard observables in mesonic $b \rightarrow s ν\barν$ decays ($B \rightarrow K^{(*)} ν\barν$, $B_s \rightarrow ϕν\barν$) probe only two combinations of short-distance Wilson coefficients, $|C_L + C_R|$ and $|C_L - C_R|$, the angular observables in $Λ_b \rightarrow Λ(\rightarrow pπ^-)ν\barν$ provide access to the orthogonal combinations $|C_R|^2 - |C_L|^2$ and $\text{Im}(C_L C_R^*)$. In particular, we identify a $T$-odd CP asymmetry, $A_5$, that directly probes CP-violating phases in the short-distance effective Hamiltonian. We present Standard Model predictions for the branching ratio and all angular observables using lattice QCD form factors, and evaluate the projected new physics sensitivity at the FCC-ee. Our results demonstrate that baryonic angular observables are essential for resolving parameter degeneracies and for completely characterizing the chiral and CP structure of possible new physics in $b \rightarrow s ν\barν$ transitions.
Comments42 pages, 8 figures
