B meson decays using heavy HISQ b quarks

标准模型对夸克口味变化相互作用的适应性包括先验的未知变量，即CKM矩阵的元素，这些变量参数化了我们对导致夸克口味变化相互作用的潜在物理的无知。此外，通过几十年的实验和理论努力确定的CKM矩阵的值揭示了一个无法解释的结构，它表明了一组未知的自然规则，但不是我们标准模型的一部分。详细研究这种衰变可能有助于阐明这些规律并发现新的物理定律。本项目通过改进从实验测量中提取与B介子衰变相关的CKM矩阵元素所需的强子矩阵元素的计算，朝着这个方向工作。这不仅对发现潜在的新物理学所起的作用很重要，而且因为我们利用实验结果的能力取决于类似的精确计算。在接下来的几年里，欧洲核子研究中心的大型强子对撞机将继续对B介子衰变产生新的结果。与此同时，日本超级KEK加速器设施的Belle-II探测器将收集前所未有的B介子衰变数据。使用一种称为点阵QCD的从头算方法，我们计算了这些衰变所需的强子矩阵元素。晶格QCD是唯一的工具，可用于计算这些非摄动矩阵元素，而不必诉诸于不受控制的近似。我们将使用在格拉斯哥开发的一种方法，以完全相对论的方式处理b夸克，从而消除目前在晶格上b介子计算中系统不确定性的主要来源。初步结果表明，该程序将是成功的，并且可以减少误差，从而使晶格QCD结果的精度达到或超过实验结果。

The Standard Model accommodation of quark flavour-changing interactions includes a priori unknown variables, the elements of the CKM matrix, that parametrize our ignorance of the underlying physics responsible for quark flavour-changing interactions. Furthermore, the values of the CKM matrix, determined by decades of experimental and theoretical effort, reveal an unexplained structure that suggests a set of unknown rules obeyed by Nature, but not part of our Standard Model. Studying such decays in detail may help to elucidate these rules and discover new laws of physics. This project works in this direction by improving the calculation of hadronic matrix elements required to extract the CKM matrix elements, related to B meson decays, from experimental measurements. This is important not only for the role played in uncovering potential new physics, but also because our ability to leverage experimental results hinges on similarly precise calculations. Over the coming years, there will continue to be new results for B meson decays from LHCb at CERN. Meanwhile, an unprecedented amount of data will be collected for decays of B mesons at the Belle-II detector at the Super KEK accelerator facility in Japan. Using an ab initio approach called Lattice QCD, we calculate the required hadronic matrix elements for these decays. Lattice QCD is the only tool available to calculate these non-perturbative matrix elements without having to resort to uncontrolled approximations. We will use an approach, developed at Glasgow, to treat the b quarks in a fully relativistic way, thereby removing the current dominant source of systematic uncertainty in B meson calculations on the lattice. Initial results suggest this program will be successful and a reduction in errors will be possible that allows the precision of lattice QCD results to match or exceed that from experiment.