本研究利用格点QCD计算$B_s\to K \ell ν$衰变的形状因子，结合实验确定CKM矩阵元$|V_{ub}|$，并给出可检验轻子味普适性的R比值结果。
摘要：
半轻$B_s \to K \ell ν$衰变提供了另一种b衰变道，可用于确定CKM矩阵元$|V_{ub}|$，并获得R比值以探究轻子味普适性破坏。CKM矩阵元的结果还有助于厘清遍举与单举衰变分析之间存在的差异。我们采用含畴壁轻夸克和相对论性b夸克的格点QCD计算衰变形状因子。我们分析了三种格点间距下的数据，其中幺正π介子质量低至268 MeV。我们将数值结果插值/外推至物理夸克质量和连续极限，得到了在模拟可及的$q^2$范围内、带完整误差预算的矢量形状因子$f_+(q^2)$和标量形状因子$f_0(q^2)$。我们对不同格点合作组的形状因子结果之间存在的张力给出了一种可能的解释。我们采用近期提出的贝叶斯推断方法，进行不依赖模型和截断的z参数化拟合，将结果拓展至整个允许的运动学范围。我们的结果可与$B_s \to D_s$和$B_s\to K$半轻衰变的实验测量相结合，确定$|V_{ub}|=3.8(6)\times 10^{-3}$，目前该误差主要来自实验。我们还计算了微分分支比和两类R比值：一类是常用的R比值，另一类是更适合检验轻子味普适性的变体。
英文摘要：
Semileptonic $B_s \to K \ell ν$ decays provide an alternative $b$-decay channel to determine the CKM matrix element $|V_{ub}|$, and to obtain a $R$-ratio to investigate lepton-flavor-universality violations. Results for the CKM matrix element may also shed light on the discrepancies seen between analyses of inclusive or exclusive decays. We calculate the decay form factors using lattice QCD with domain-wall light quarks and a relativistic $b$-quark. We analyze data at three lattice spacings with unitary pion masses down to $268\,\mathrm{MeV}$. Our numerical results are interpolated/extrapolated to physical quark masses and to the continuum to obtain the vector and scalar form factors $f_+(q^2)$ and $f_0(q^2)$ with full error budgets at $q^2$ values spanning the range accessible in our simulations. We provide a possible explanation of tensions found between results for the form factor from different lattice collaborations. Model- and truncation-independent $z$-parameterization fits following a recently proposed Bayesian-inference approach extend our results to the entire allowed kinematic range. Our results can be combined with experimental measurements of $B_s \to D_s$ and $B_s\to K$ semileptonic decays to determine $|V_{ub}|=3.8(6)\times 10^{-3}$. The error is currently dominated by experiment. We compute differential branching fractions and two types of $R$ ratios, the one commonly used as well as a variant better suited to test lepton-flavor universality.
Inclusive and exclusive semileptonic decays of heavy mesons on the lattice
High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；University of Southampton（南安普顿大学）；SOKENDAI (The Graduate University for Advanced Studies)（高级研究院索卡代）；CERN（欧洲核子研究中心）
Inclusive semileptonic $D_s\to X_s\ell\barν$ decays from lattice QCD: continuum and chiral extrapolation
High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；PRISMA++ Cluster of Excellence & Institut für Kernphysik, Johannes-Gutenberg-Universität Mainz（美因茨约翰内斯·古腾堡大学 PRISMA++ 卓越集群与核物理研究所）；School of Physics and Astronomy, University of Southampton（南安普顿大学物理与天文学院）；STAG Research Center, University of Southampton（南安普顿大学 STAG 研究中心）；School of High Energy Accelerator Science, SOKENDAI (The Graduate University for Advanced Studies)（高级研究院（SOKENDAI）高能加速器科学学校）；RIKEN Center for Computational Science (R-CCS)（理化学研究所计算科学中心）；CERN, Theoretical Physics Department（欧洲核子研究中心理论物理部）
