论文标题
美元
$|V_{cb}|$, LFU and $SU(3)_F$ symmetry breaking in $B_{(s)} \to D_{(s)}^{(*)} \ell ν_\ell$ decays using Lattice QCD and Unitarity
论文作者
论文摘要
我们介绍了基于单位性的分散矩阵（DM）方法的应用，用于提取CKM矩阵元素$ | v_ {cb} | $从独家半蛋白质$ b _ {（s s）} \ do d _ {（s）} {（s s）}^{（*）}^{（*）}^eell $ ell $ el $ ell $ ell $ ell $ ell $ ell $ ell $ eell $ end的实验数据中。 DM方法允许实现非扰动的，独立于模型的确定半抑制性形式因素的动量依赖性。从晶格结果开始，以4个弹药转移的较大值和实现非扰动的单位性结合开始，在其整个运动学范围内的形式因素的行为是在没有引入其动量依赖性的任何明确参数化的情况下获得的。我们将四个独家半植物$ b _ {（s）} \ to d _ {（s）}^{（*）} \ellν_\ ell $衰减并从实验数据中提取$ | v_ {cb} | $。四个频道的平均值为$ | v_ {cb} | =（41.2 \ pm 0.8）\ cdot 10^{ - 3} $，它与$1σ$级别的最新包含性确定兼容。我们还通过计算每个通道的分支分数的$τ/\ ell $比率的纯理论估计来解决Lepton风味普遍性的问题，其中$ \ ell $是轻质的Lepton。如果是光观众夸克，我们获得了$ r（d^*）= 0.275（8）$和$ r（d）= 0.296（8）$，它们与$1.3σ$内的相应实验值兼容。对于一个奇怪的观众夸克，我们获得$ \ textit {r}（d_s^*）= 0.2497（60）$和$ \ textit {r}（d_s）= 0.298（5）$。 $ r（d_s^*）$和$ r（d^*）$的不同值可能反映$ su（3）_f $ symmetry Breaking效果，这些效果似乎存在于某些晶格形式中，尤其是在后座的较大值下。
We present an application of the unitarity-based dispersion matrix (DM) approach to the extraction of the CKM matrix element $|V_{cb}|$ from the experimental data on the exclusive semileptonic $B_{(s)} \to D_{(s)}^{(*)} \ell ν_\ell$ decays. The DM method allows to achieve a non-perturbative, model-independent determination of the momentum dependence of the semileptonic form factors. Starting from lattice results available at large values of the 4-momentum transfer and implementing non-perturbative unitarity bound, the behaviour of the form factors in their whole kinematical range is obtained without introducing any explicit parameterization of their momentum dependence. We consider the four exclusive semileptonic $B_{(s)} \to D_{(s)}^{(*)} \ell ν_\ell$ decays and extract $|V_{cb}|$ from the experimental data for each transition. The average over the four channels is $|V_{cb}| = (41.2 \pm 0.8) \cdot 10^{-3} $, which is compatible with the latest inclusive determination at $1σ$ level. We address also the issue of Lepton Flavour Universality by computing pure theoretical estimates of the $τ/\ell$ ratios of the branching fractions for each channel, where $\ell$ is a light lepton. In the case of a light spectator quark we obtain $R(D^*) = 0.275(8)$ and $R(D) = 0.296(8)$, which are compatible with the corresponding experimental values within $1.3σ$. In the case of a strange spectator quark we obtain $\textit{R}(D_s^*) =0.2497(60)$ and $\textit{R}(D_s) = 0.298(5)$. The different values for $R(D_s^*)$ and $R(D^*)$ may reflect $SU(3)_F$ symmetry breaking effects, which seem to be present in some of the lattice form factors, especially at large values of the recoil.
