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arXiv 1708.09148hep-ex
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LHCb半轻子衰变轻子味普适性的检验

Tests of Lepton Flavour Universality with Semileptonic Decays at LHCb

Federico Betti

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摘要：

可观测的$\mathcal{R} \left( D^{(*)} \right) = \mathcal{B}\left( B^{0}\to D^{(*)-} τ^{+} ν_τ \right) / \mathcal{B}\left( B^{0}\to D^{(*)-} μ^{+} ν_μ \right)$是轻子普适性破坏的探针，因此它对新物理过程很敏感。$\mathcal{R} \left( D^{(*)} \right)$测量值的当前组合与标准模型预测值不同，具有$4σ$显著性。在LHCb进行了使用三管$τ$衰变的$\mathcal{R} ( D^* )$测量，得到了$\mathcal{R}(D^*) = 0.285 \pm 0.019 (\text{stat}) \pm 0.025(\text{syst}) \pm 0.014 (\text{ext})$。该值与用$τ\to μν_τ\barν_μ$衰变获得的LHCb结果相结合，给出了${\mathcal{R}}(D^*) = 0.306 \pm 0.016 (\text{stat}) \pm 0.022 (\text{syst})$，与世界平均值一致，比SM预测高2.1个标准差。

英文摘要：

The observable $\mathcal{R} \left( D^{(*)} \right) = \mathcal{B}\left( B^{0}\to D^{(*)-} τ^{+} ν_τ \right) / \mathcal{B}\left( B^{0}\to D^{(*)-} μ^{+} ν_μ \right)$ is a probe for Lepton Universality violation, so it is sensitive to New Physics processes. The current combination of the measurements of $\mathcal{R} \left( D^{(*)} \right)$ differs from Standard Model predictions with a $4σ$ significance. A measurement of $\mathcal{R} ( D^* )$ using three-prong $τ$ decays has been performed at LHCb, resulting in $\mathcal{R}(D^*) = 0.285 \pm 0.019 (\text{stat}) \pm 0.025(\text{syst}) \pm 0.014 (\text{ext})$. This value, combined with the LHCb result obtained with $τ\to μν_τ\barν_μ$ decays, gives ${\mathcal{R}}(D^*) = 0.306 \pm 0.016 (\text{stat}) \pm 0.022 (\text{syst})$, consistent with the world average and 2.1 standard deviations above the SM prediction.

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