发表机构
Amity International School; Centre for High Energy Physics, Kyungpook National University（Amity国际学校; 庆北大学高能物理中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文研究暗费米子圈真空极化修正的 $Z'$ 传播子对 $B \to K^*\mu^+\mu^-$ 角观测量 $P'_5$ 反常的影响，通过参数扫描和 $\chi^2$ 拟合发现矢量主导且手征不对称的解，将偏差降低约96%，为LHCb Run 3提供基准。
AI 中文摘要
稀有味改变中性流衰变，如 $B \to K^{*}\mu^{+}\mu^{-}$，为超越标准模型（SM）的物理提供了灵敏的探针，因为这类衰变在树图级别被禁止，仅通过圈诱导过程产生。角分析给出了对短距离动力学敏感的观测量。优化观测量 $P'_5$ 在 $q^{2}\in[1.1,6.0]\\,\mathrm{GeV}^{2}$ 区间内显示出与标准模型预测约 $3\sigma$ 的持续偏差，这促使人们修改 Wilson 系数。本文研究了一个具有理论动机的框架，其中 Dirac 暗费米子 $\chi$ 的真空极化修改了重 $Z'$ 玻色子的传播子，从而诱导出对 $C_{9}(q^{2})$ 的动量依赖贡献。圈修正后的传播子被纳入 $b\to s\ell^{+}\ell^{-}$ 的有效弱哈密顿量中。使用 \texttt{flavio} 计算了分箱平均的角观测量，并对 $Z'$ 耦合的不同手征结构扫描了 $34{,}997$ 个参数点。$\chi^{2}$ 分析确定了偏好区域，这些区域是矢量主导且手征不对称的。最佳拟合解显著缓解了 $P'_5$ 张力，将中心 $q^{2}$ 箱中的偏差降至 $0.12\sigma$，相对于标准模型改善了约 $96\\%$。这一改善由树图级 $Z'$ 交换驱动，诱导出 $\Delta C_{9}\simeq-1.2$，与全局拟合一致，并与其他角观测量及 $B_{s}\to\mu^{+}\mu^{-}$ 兼容。暗费米子真空极化给 $C_{9}$ 增加了次主导的 $q^{2}$ 依赖；它不主导拟合，但提供了独特的阈值结构，可通过更精细的分箱进行检验。这些结果表明，$Z'$ 门户到暗费米子为 $P'_5$ 反常提供了现象学上一致的解释，并为 LHCb Run~3 分析提供了具体基准。
英文摘要
Rare flavour changing neutral current decays such as $B \to K^{*}μ^{+}μ^{-}$ provide sensitive probes of physics beyond the Standard Model (SM), being forbidden at tree level and arising only through loop induced processes. Angular analyses yield observables sensitive to short distance dynamics. The optimized observable $P'_5$ shows a persistent $\sim 3σ$ deviation from SM predictions in $q^{2}\in[1.1,6.0]\,\mathrm{GeV}^{2}$, motivating modified Wilson coefficients. A theoretically motivated framework is investigated in which vacuum polarization of a Dirac dark fermion $χ$ modifies the propagator of a heavy $Z'$ boson, inducing a momentum dependent contribution to $C_{9}(q^{2})$. The loop corrected propagator is incorporated into the effective weak Hamiltonian for $b\to s\ell^{+}\ell^{-}$. Bin averaged angular observables are computed with \texttt{flavio}, and $34{,}997$ parameter points are scanned over different chiral structures of the $Z'$ couplings. A $χ^{2}$ analysis identifies preferred regions that are vector dominated and chirally asymmetric. The best fit solution significantly alleviates the $P'_5$ tension, reducing the deviation in the central $q^{2}$ bin to $0.12σ$, an improvement of approximately $96\%$ relative to the SM. This improvement is driven by tree level $Z'$ exchange, which induces $ΔC_{9}\simeq-1.2$, consistent with global fits and compatible with other angular observables and $B_{s}\toμ^{+}μ^{-}$. Dark fermion vacuum polarization adds a subleading $q^{2}$ dependence to $C_{9}$; it does not dominate the fit, but supplies a distinctive threshold structure testable with finer binning. These results show that a $Z'$ portal to a dark fermion provides a phenomenologically consistent description of the $P'_5$ anomaly and a concrete benchmark for LHCb Run~3 analyses.
