论文标题
$ b^0 _ {（s）} \toπ^0π^0 $和$ b^0 _ {（s）} \toη$模式和对应的$ cp $ dymmetries的前景
Prospects for $B^0_{(s)}\toπ^0π^0$ and $B^0_{(s)}\toηη$ modes and corresponding $CP$ asymmetries at Tera-$Z$
论文作者
论文摘要
测量$ b^0 _ {（s）} \toπ^0π^0 $和$ b^0 _ {（s）} \toη$衰减的物理潜力通过TERA- $ Z $相位的CEPC或FCC-EE的Tera- $ Z $阶段在本文中进行了研究。我们提出了一个具有高能量分辨率和出色的分离功率的电磁热量表（ECAL），以有效地从具有高光子多重性的HADRONIC最终状态重建$π^0 $和$η$。由此产生的$ b $ -Meson质量分辨率约为30 meV，允许在$ b^0 $和$ b_s^0 $之间进行3 $σ$分离。在$ b $ -JET标签的帮助下，相对敏感性对$ b^0 \toπ^0π^0 $，$ b^0_s \toπ^0π^0 $，$ b^0 \toη$，以及$ b^0_s \ tohη$ to tera- $ z $ as tera- $ z $ as as Tera- $ z $ as as Tera- $ z $ as as Tera- $ z $ as as Tera- $ z $ as as Tera- $ z $ as as Tera-$ z $ as as tera-n $ 0.45％均为0.45％，4.5％，和4.5％，18％，和4.5％。还讨论了它们对各种检测器性能的依赖。此外，$ b^0 \toπ^0π^0 $及其两个与同胞相关的模式特别注意，因为它们在确定CKM角$α$（$ ϕ_2 $）中的作用。评估了其分支比率的预期精度和$ CP $ -Asmmemetry在TERA- $ Z $上的测量。我们表明，时间集成的$ b^0 \toπ^0π^0 $ $ $ $ $ cp $不对称的测量是与$ b $ -factory的互补的。 $α$结合$ z $ - 和$ b $ - $ $ $ $ $α$的精确度达到$ 0.4^\ Circ $，低于Isospin Breaking附加的系统不确定性。
The physics potential of measuring $B^0_{(s)}\toπ^0π^0$ and $B^0_{(s)}\toηη$ decays via four-photon final states at Tera-$Z$ phase of CEPC or FCC-ee is investigated in this paper. We propose an electromagnetic calorimeter (ECAL) with both high energy resolution and excellent separation power to efficiently reconstruct $π^0$ and $η$ from hadronic final states with high photon multiplicity. The resulting $B$-meson mass resolution is approximately 30 MeV, allowing 3 $σ$ separation between $B^0$ and $B_s^0$. With the assistance of the $b$-jet tagging, the relative sensitivities to $B^0\toπ^0π^0$, $B^0_s\toπ^0π^0$, $B^0\toηη$, and $B^0_s\toηη$ signal strengths at Tera-$Z$ are projected as 0.45%, 4.5%, 18%, and 0.95%, respectively. Their dependence on various detector performances is also discussed. In addition, $B^0\toπ^0π^0$ and its two isospin-related modes are paid special attention due to their roles in the determination of the CKM angle $α$ ($ϕ_2$). The anticipated precisions of their branching-ratio and $CP$-asymmetry measurements at Tera-$Z$ are evaluated. We show that the measurement of the time-integrated $B^0\toπ^0π^0$ $CP$ asymmetry at Tera-$Z$ is complementary to $B$-factory ones. The precision on $α$ combining $Z$- and $B$-factory results reaches $0.4^\circ$, lower than the systematic uncertainties attached to isospin breaking.
