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arXiv 1504.07928hep-phhep-ex
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一般$Z^\prime$模型中轻子味破坏的$B$衰变

Lepton-flavour violating $B$ decays in generic $Z^\prime$ models

Andreas Crivellin, Lars Hofer, Joaquim Matias, Ulrich Nierste, Stefan Pokorski, Janusz Rosiek

备注：
7 pages, 4 figures, constraints from B->Knunu added, typos corrected
发表信息：
Phys. Rev. D 92, 054013 (2015)
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摘要：

LHCb报告了$b\to sμ^+μ^-$跃迁偏离标准模型的情况，其中一个新的中性规范玻色子是解释的主要候选者。由于这种规范玻色子必须以非普适的方式与μ子和电子耦合，才能解释$R_K$，因此研究轻子味也被违反的可能性是很有趣的，特别是考虑到$h\toτ^\pmμ^\mp$中的CMS过剩。本文探讨了发现轻子味破坏模$B\to K^{(*)}τ^\pmμ^\mp$、$B_s\to τ^\pmμ^\mp$和$B\to K^{(*)} μ^\pm e^\mp$、$B_s\to μ^\pm e^\mp$的前景。为此，我们考虑一个简化的模型，其中新的物理效应起源于一个额外的中性规范玻色子（PDMATHAMT）与夸克和轻子的一般耦合。从$τ\to3μ$，$τ\toμν\barν$，$μ\to eγ$，$g_μ-2$，半轻子$b\to sμ^+μ^-$衰变，$B\to K^{(*)}νν$和$B_s$ -$\overline{B}_s$混合的约束进行检查。从这些衰变，我们确定的轻子味违反$B$衰变的衰变率的上限。对于矢量（左手）轻子耦合，$Br(B\to Kνν)$将LFV $B$衰变的分支比限制为小于$8\times 10^{-5} (2\times 10^{-5})$。然而，通过对$B_s$ -- $\overline{B}_s$、$τ\to3μ$、$τ\toμν\barν$和其他稀有衰变的联合分析，可以得到更强的边界。边界取决于对$B_s$ - $\overline{B}_s$混合的贡献之间的微调量。允许在百分比水平上进行微调，我们发现$10^{-6}$阶的上界为$τμ$最终状态的分支比，而$B_s\to μ^\pm e^\mp$被强烈抑制，只有$B\to K^{(*)} μ^\pm e^\mp$可以通过实验获得（具有$10^{-7}$阶的分支比）。

英文摘要：

LHCb has reported deviations from the Standard Model in $b\to sμ^+μ^-$ transitions for which a new neutral gauge boson is a prime candidate for an explanation. As this gauge boson has to couple in a flavour non-universal way to muons and electrons in order to explain $R_K$, it is interesting to examine the possibility that also lepton flavour is violated, especially in the light of the CMS excess in $h\toτ^\pmμ^\mp$. In this article, we investigate the perspectives to discover the lepton-flavour violating modes $B\to K^{(*)}τ^\pmμ^\mp$, $B_s\to τ^\pmμ^\mp$ and $B\to K^{(*)} μ^\pm e^\mp$, $B_s\to μ^\pm e^\mp$. For this purpose we consider a simplified model in which new-physics effects originate from an additional neutral gauge boson ($Z^\prime$) with generic couplings to quarks and leptons. The constraints from $τ\to3μ$, $τ\toμν\barν$, $μ\to eγ$, $g_μ-2$, semi-leptonic $b\to sμ^+μ^-$ decays, $B\to K^{(*)}νν$ and $B_s$--$\overline{B}_s$ mixing are examined. From these decays, we determine upper bounds on the decay rates of lepton flavour violating $B$ decays. $Br(B\to Kνν)$ limits the branching ratios of LFV $B$ decays to be smaller than $8\times 10^{-5} (2\times 10^{-5})$ for vectorial (left-handed) lepton couplings. However, much stronger bounds can be obtained by a combined analysis of $B_s$--$\overline{B}_s$, $τ\to3μ$, $τ\toμν\barν$ and other rare decays. The bounds depend on the amount of fine-tuning among the contributions to $B_s$--$\overline{B}_s$ mixing. Allowing for a fine-tuning at the percent level we find upper bounds of the order of $10^{-6}$ for branching ratios into $τμ$ final states, while $B_s\to μ^\pm e^\mp$ is strongly suppressed and only $B\to K^{(*)} μ^\pm e^\mp$ can be experimentally accessible (with a branching ratio of order $10^{-7}$).

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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