Virtual Photon Emission in Leptonic Decays of Pseudoscalar Mesons
R. Frezzotti, G. Gagliardi, V. Lubicz, G. Martinelli, F. Mazzetti, C. Sachrajda, F. Sanfilippo, S. Simula, N. Tantalo
备注：
11 pages, 16 figures. Talk presented at the 38th International Symposium on Lattice Field Theory (Lattice 2021), 26-30 July, 2021, Zoom/Gather@Massachusetts Institute of Technology
We present a preliminary non-perturbative lattice calculation of the form factors entering the processes $K\to \ell\,ν_\ell\,\ell'^+\,\ell'^-$ and of the corresponding branching ratios. These form factors describe the interaction between the mediating virtual photon and the internal hadronic structure of the meson. By separating them from the point-like contribution to the matrix element we are able to isolate and reconstruct the structure-dependent contribution to the decay width. Our numerical analysis employs only one gauge ensemble and so it is affected by systematic uncertainties due to the missing continuum and physical point extrapolation. Despite this, we already find a reasonable agreement with the experimental data and with the next to leading order Chiral Perturbation Theory predictions. The method is general and can be applied to any pseudoscalar meson, though for heavier mesons the possibility of internal lighter states becomes problematic and still needs a proper study. A non-perturbative, model-independent lattice evaluation of these processes would allow further progress in the theoretical predictions of SM hadronic quantities and in the search of New Physics.
In Carrasco et al. we have recently proposed a method to calculate $O(e^2)$ electromagnetic corrections to leptonic decay widths of pseudoscalar mesons. The method is based on the observation that the infrared divergent contributions (that appear at intermediate stages of the calculation and that cancel in physical quantities thanks to the Bloch-Nordsieck mechanism) are universal, i.e. depend on the charge and the mass of the meson but not on its internal structure. In this talk we perform a detailed analysis of the finite-volume effects associated with our method. In particular we show that a…
We study the radiative leptonic decays $P\to\ellν_\ell\,\ell^{\prime\,+}\ell^{\prime\,-}$, where $P$ is a pseudoscalar meson and $\ell$ and $\ell^\prime$ are charged leptons. In such decays the emitted photon is off-shell and, in addition to the "point-like" contribution in which the virtual photon is emitted either from the lepton or the meson treated as a point-like particle, four structure-dependent (SD) form factors contribute to the amplitude. We present a strategy for the extraction of the SD form factors and implement it in an exploratory lattice computation of the decay rates for the f…
Hopping Parameter Analysis of Leptonic and Semi-Leptonic Heavy-Light Decays
我们研究了D和B介子的轻子和半轻子衰变。利用两点函数的跳跃参数展开（HPE），我们可以连续地改变赝标质量，从m_D以下到m_B。我们计算了赝标衰变常数f_D和f_B，并观察到与静态极限计算值的一致性。{}根据三点函数的测量，我们计算与衰减\bar B -> D1 \bar nu_l相关的矩阵元素，并提取Isgur-Wise函数xi（v. v '）。HPE使我们能够在恒定v. v '下自由改变初态赝标质量，并研究了对重夸克极限的1/m_Q修正。
Leptonic Decays of Charged Pseudoscalar Mesons - 2015
本文综述了$π^\pm$、$K^\pm$、$D^{\pm}$、$D_s^\pm$和$B^\pm$赝标介子的纯轻子衰变物理。所测得的衰变率与组分夸克的相关弱相互作用CKM矩阵元和与介子中夸克和反夸克波函数重叠相关的强相互作用参数（称为衰变常数$f_P$）的乘积有关。用{ \it ab initio}格点QCD模拟方法，可以得到$π^\pm$、$K^\pm$、$D^{\pm}$、$D_s^\pm$和$B^\pm$介子的轻子衰变常数，理论不确定度可控，计算精度高.实验轻子衰变率测量和理论衰变常数计算相结合，使几个元素的CKM矩阵内的标准模型的确定。这些测定与半轻子衰变的结果是竞争性的，也是互补的，因为它们对不同的夸克变味电流敏感。它们也可以用来测试CKM矩阵的第一行和第二行的酉性。相反地，采用由么正性预测的CKM元素，可以推断出$f_P$的“实验”值，其可以与理论进行比较。这些提供了格点QCD方法的测试，假设新物理对轻子衰变的贡献在当前的精度水平上可以忽略不计。这篇评论是粒子数据组2016年版文章的基础，更新了参考文献中的版本。[1-3]中所述。
We present a lattice QCD computation and preliminary results for the leptonic decay constants of the pseudoscalar mesons $K$, $D$ and $D_{s}$ in the isosymmetric QCD limit. The computation is based on simulations of $N_f = 2+1+1$ dynamical quarks performed by the Extended Twisted Mass Collaboration (ETMC), where the light, strange and charm quark masses are all tuned at their physical values. We also present preliminary unitarity checks for the first and second rows of the Cabibbo-Kobayashi-Maskawa matrix.
Real radiative decays of heavy pseudoscalar mesons
University of Edinburgh（爱丁堡大学）；RIKEN Center for Computational Science（理化学研究所计算科学中心）；CERN（欧洲核子研究中心）；High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；University of Liverpool（利物浦大学）
Pseudoscalar-pole diagrams are an important component of estimates of the hadronic light-by-light (HLbL) contribution to the muon $g-2$. We report on our computation of the transition form factors $\mathcal{F}_{P \rightarrow γ^* γ^*}$ for the neutral pseudoscalar mesons $P=π^0$ and $η$. The calculation is performed using twisted-mass lattice QCD with physical quark masses. On the lattice, we have access to a broad range of (space-like) photon four-momenta and therefore produce form factor data complementary to the experimentally accessible single-virtual direction, which directly leads to an e…
The remarkable recent progress in the precision of Lattice QCD computations for a number of physical quantities relevant for flavour physics has motivated the introduction of isospin-breaking effects, including in particular electromagnetic corrections, to the computations. The isospin breaking corrections are necessary to fully exploit this improved precision for the determination of the fundamental parameters of the Standard Model, including the CKM matrix elements, and to look for deviations from experimental measurements which might signal the presence of new physics. Together with colleag…
