Belle II 实验中 B±→ωK± 与 B±→ωπ± 衰变的分支比与直接 CP 不对称性测量

Abstract

我们报告了基于详尽的蒙特卡洛模拟衰变模型，对无味强子衰变 B⁺→ωK⁺ 和 B⁺→ωπ⁺ 的支分数及直接 CP 电荷不对称性进行可行性研究的结果。 此模拟采用完整的 LS1 探测器几何结构和响应，针对 Υ(4S) 共振下相当于 362 fb⁻¹ 的数据量（约 (387±1)×10⁶ 对 B B̄）。ω→π⁺π⁻π⁰ 末态通过基于事件形状和运动学特征训练的多变量分类器进行重建，以优化信号选择并抑制连续体背景。信号产额通过对束约束质量 M_bc 和能量差 ΔE 的无分箱扩展极大似然拟合提取。我们评估支分数在 10⁻⁶ 量级的统计精度，并预计 CP 不对称灵敏度达百分数水平。 我们从控制信道 B⁺→D̄⁰π⁺ 样本中逐事件提取数据对 MC 的校正因子，校正跟踪效率、PID 及分类器性能，以降低系统偏差并增强灵敏度预测。 最终结果将在未来 Belle II 实际数据去盲后给出。本研究验证了分析策略，并表明我们已做好应对即将到来数据集的准备。

We report on feasibility studies of branching fractions and direct CP-violating charge asymmetries in the charmless hadronic decays B⁺→ωK⁺ and B⁺→ωπ⁺ based on detailed Monte Carlo simulations of our decay model. The simulation uses the full LS1 detector geometry and response corresponding to 362 fb⁻¹ at the Υ(4S) resonance, equivalent to (387±1)×10⁶ B B̄ pairs. The ω→π⁺π⁻π⁰ final states are reconstructed with a multivariate classifier trained on event-shape and kinematic features to optimize signal selection and suppress continuum backgrounds. Signal yields are extracted via unbinned extended maximum-likelihood fits to the beam-constrained mass M_bc and energy difference ΔE. We assess the expected statistical precision on branching fractions at the 10⁻⁶ level and project sensitivity to CP asymmetries at the few-percent level. We derive event-by-event data-to-MC scale factors from control-channel B⁺→D̄⁰π⁺ samples—correcting tracking, PID, and classifier performance—to reduce systematic biases and strengthen our sensitivity projections. Final results will be obtained upon unblinding of real data in future Belle II analyses. These studies validate our analysis strategy and demonstrate readiness for the upcoming dataset.