$B_{(s)} \to ρρ、ρK^\ast$ 和 $K^\ast K^\ast$ 衰变中的极化分数和螺旋度相关的 CP 不对称性
Polarization fractions and helicity-dependent CP asymmetries in $B_{(s)} \to ρρ, ρK^\ast$ and $K^\ast K^\ast$ decays
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中文总结 AI 辅助
研究利用 pQCD 计算对 $B_{(s)} \to \rho\rho、\rho K^\ast$ 和 $K^\ast K^\ast$ 衰变进行唯象分析，扩展了先前研究。对部分模式的分支比和极化分数预测与实验吻合，但存在差异，凸显解决两体 $B$ 衰变极化难题需进一步理论研究。
中文摘要 AI 辅助
本文利用最先进的微扰 QCD（pQCD）计算对 $B_{(s)} \to \rho\rho、\rho K^\ast$ 和 $K^\ast K^\ast$ 衰变进行了唯象分析。近期 LHCb 和 Belle II 合作组的极化测量显著提高了极化分数精度并首次全面确定了极化相关的 CP 不对称性，促使了本研究。此工作扩展了之前关于无 charm 两体 $B$ 衰变的综合 pQCD 研究，特别关注极化可观测量，尤其是各螺旋度态的 CP 不对称性。对 $B^0 \to K^{\ast 0} {\bar K}^{\ast 0}$ 和 $B^+ \to \rho^0 K^{\ast +}$ 模式的分支比和纵向极化分数的预测与新实验数据吻合良好，但 $B_s \to K^{\ast 0} {\bar K}^{\ast 0}$ 的计算纵向极化分数比 LHCb 测量值大得多，且 $B^+ \to \rho^0 K^{\ast +}$ 中预测的（螺旋度相关）CP 不对称性比观测值小约 $30\%$。这些差异表明不同拓扑振幅间存在复杂相互作用，凸显了进一步理论研究以解决两体 $B$ 衰变为矢量介子中长期存在的极化难题的必要性。
英文摘要
In this paper, we present a phenomenological analysis of $B_{(s)} \to ρρ, ρK^\ast$ and $K^\ast K^\ast$ decays using state-of-the-art perturbative QCD (pQCD) calculations. Our study is primarily motivated by recent polarization measurements from the LHCb and Belle II collaborations, which have significantly improved the precision of polarization fractions and enabled the first full determination of polarization-dependent CP asymmetries. This work extends the comprehensive pQCD study of charmless two-body $B$ decays reported in our previous paper [Chin. Phys. C 46 (2022) 123103], with a particular focus on polarization observables, especially the CP asymmetries in each helicity state, which reflect distinct orbital angular momentum configurations between the two vector mesons. Our predictions for the branching ratios and longitudinal polarization fractions in the $B^0 \to K^{\ast 0} {\bar K}^{\ast 0}$ and $B^+ \to ρ^0 K^{\ast +}$ modes are in good agreement with the new experimental data. However, the calculated longitudinal polarization fraction for $B_s \to K^{\ast 0} {\bar K}^{\ast 0}$ is significantly larger than the LHCb measurement. Moreover, the predicted (helicity-dependent) CP asymmetries in $B^+ \to ρ^0 K^{\ast +}$ are about $30 \%$ smaller than the observed values. These discrepancies point to a rich interplay between different topological amplitudes, highlighting the need for further theoretical investigation to resolve the long-standing polarization puzzle in two-body $B$ decays into vector mesons.
