We propose a novel method to probe the persistent hints of lepton flavor universality violation observed in semileptonic $B$ decays. Relying on the specific properties of the Belle II experiment, it consists in comparing the inclusive rates of $\mathrm{\Upsilon }(4S)\to e^{\pm }{\mu }^{\mp }X$, $\mathrm{\Upsilon }(4S)\to {\mu }^{\pm }{\tau }_{\mathrm{had}}^{\mp }X$ and $\mathrm{\Upsilon }(4S)\to e^{\pm }{\tau }_{\mathrm{had}}^{\mp }X$. We show that such a measurement can be directly related to the ratio $R(X{)}_{\tau \ell }\equiv \mathrm{\Gamma }(B\to X\tau \nu )/\mathrm{\Gamma }(B\to X\ell \nu )$ ($\ell =e$ or $\mu$), once appropriate experimental cuts are applied to suppress the effects of neutral $B$ mixing and leptons emitted through charm or tau decays. Such a measurement would thus constitute an additional and potentially competitive probe of lepton flavor universality in $b\to c\ell \nu$ transitions, complementary to existing exclusive measurements, accessible in the Belle II environment.

中文翻译：

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在ϒ(4S) 衰变中测试轻子风味的普遍性

我们提出了一种新方法来探测在半轻子中观察到的轻子风味普遍性违反的持续暗示 $乙$腐烂。依靠 Belle II 实验的特定属性，它包括比较包含率$\mathrm{⒈}(4秒)\to {\mathrm{电子}}^{\pm }{\mu }^{\mp }X$, $\mathrm{⒈}(4秒)\to {\mu }^{\pm }{\tau }_{有}^{\mp }X$ 和 $\mathrm{⒈}(4秒)\to {\mathrm{电子}}^{\pm }{\tau }_{有}^{\mp }X$. 我们表明这样的测量可以与比率直接相关$\mathrm{电阻}(X{)}_{\tau \ell }\equiv \mathrm{\Gamma }(乙\to X\tau \nu )/\mathrm{\Gamma }(乙\to X\ell \nu )$ ($\ell =\mathrm{电子}$ 或者 $\mu$)，一旦应用适当的实验削减来抑制中性的影响 $乙$通过魅力或 tau 衰变发出的混合和轻子。因此，这样的测量将构成对轻子风味普遍性的额外的和潜在的竞争性探索。$乙\to C\ell \nu$ 过渡，补充现有的独家测量，可在 Belle II 环境中访问。