Investigation on effects of new physics in transitions *
Investigation on effects of new physics in transitions *
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DOI：
10.1088/1674-1137/abf489
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发表时间：
2020-11
期刊：
影响因子：
--
通讯作者：
X. Leng;Xiaolan Mu;Z. Zou;Ying Li
中科院分区：
文献类型：
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作者：
X. Leng;Xiaolan Mu;Z. Zou;Ying Li
最近由$B\to c \ell^- \bar\nu_\ell$跃迁引起的衰变反常现象提出了关于由$c\to（s，d）\ell^+\nu_\ell$跃迁引起的$D$衰变中这种现象的问题。在实验方面，对纯轻子和半轻子$D$衰变的电流测量与标准模型的预言一致，这种一致性可以用来约束新物理（NP）的贡献。在这项工作中，我们通过假设描述$c\to（s，d）\ell^+\nu_\ell$跃迁的一般有效哈密顿量来扩展标准模型，包括完整的四费米子算符集。在最新的实验数据中，我们对每个算子对应的Wilson系数进行了最小拟合。结果表明，μ介子扇区中标量算符的Wilson系数为10 - 2量级，其它标量算符的Wilson系数为10 - 3量级.标量算符可能违反轻子味普适性。我们还用标量算符和张量算符的Wilson系数计算了末态矢量介子和轻子的分支分数、前后不对称性和极化率。结果表明，纯轻子衰变对标量算符非常敏感。NP对有电子的半轻子衰变的影响可以忽略不计，而对有μ子的半轻子衰变，标量算符的影响将表现在μ子的前后向不对称性和μ子的极化上。BESIII和贝儿II实验的测量结果将有助于我们检验NP效应和进一步检验新的物理模型。
Recent anomalies in decays induced by $b\to c \ell^- \bar\nu_\ell$ transitions raise the question about such phenomena in the $D$ decays induced by $c\to (s,d)\ell^+\nu_\ell$ transitions. In the experimental side, current measurements on the pure leptonic and semileptonic $D$ decays agree with the standard model predictions, such agreements can be used to constrain the new physics (NP) contributions. In this work, we extend the standard model by assuming general effective Hamiltonians describing the $c\to (s,d)\ell^+\nu_\ell$ transitions including the full set of the four-fermion operators. Within the latest experimental data, we perform a minimum $\chi^2$ fit of the Wilson coefficient corresponding to each operator. The results show that the Wilson coefficients of scalar operators in muon sector are at the order of ${\cal O}(10^{-2})$, and others are at the order of ${\cal O}(10^{-3})$. The lepton flavor universality could be violated by the scalar operators. We also calculate the branching fractions, the forward-backward asymmetries and polarizations of final vector mesons and leptons with the fitted Wilson coefficients of scalar and tensor operators. It is found that the pure leptonic decays are very sensitive to the scalar operators. The effects of NP on the semileptonic decays with electron are negligible, while for the semileptonic decays with muon the effects of scalar operators will show up in the forward-backward asymmetries and polarizations of muon of $D \to P\mu^+ \nu_\mu$. The future measurements in BESIII and Belle II experiments will help us to test effects of NP and to further test new physics models.