Search for New Physics and the precision determination of the CKM matrix element |Vub| with the Belle II experiment

迄今为止，粒子物理学的标准模型成功地描述了自然界中物质和基本粒子的相互作用。尽管标准模型取得了这样的成功，但在自然界中观察到的一系列物理现象却无法解释，一个突出的例子是宇宙中物质多于反物质。在2018年底，超级风味工厂实验Belle II将开始记录大量的b介子衰变样本。b介子的精确研究是有趣的，因为它们的衰变允许测量电荷宇称破坏的大小，从而探测粒子衰变中的物质和反物质不对称性。电荷宇称破坏的大小不能通过一次测量来确定，而是通过几个精确观测的组合来确定，任何分歧都将是标准模型之外的新物理过程的有力指示。本文的目标是对CKM矩阵元素Vub进行精确测量，该元素的绝对值是提取电荷奇偶性违背大小的重要约束之一。在实验上，Vub可以通过研究强子末态得到的半光子b介子衰变来测量。两种方法之间存在长期的紧张关系，统计显著性为3.4个标准差。造成这种张力的一个可能原因是，在使用包含衰变的最先进的测定中，使用模型函数来描述b介子内部的b夸克运动。为了消除这种可能性，本应用程序提出了一种连贯的策略，如何在Belle II实验测量的辐射和半光子b介子衰变的测量运动学分布的全局分析中同时提取该函数形式。作为准备工作和建立必要的实验技术的一部分，将使用Belle数据进行第一次分析。对介子内部b夸克运动功能形式的直接实验确定将消除在最先进的包容性Vub测量中所做的模型假设，这反过来将有助于阐明在包容性和排他性Vub测量之间观察到的差异。此外，形状函数可用于以模型无关的方式搜索辐射衰减中的新物理贡献。

Matter and interactions of elementary particles in nature are so far successfully described by the Standard Model of particle physics. Albeit this success of the Standard Model, a range of physical phenomena observed in nature cannot be explained and a prominent example is the overabundance of matter over anti-matter in the universe. At the end of the year 2018 the super flavour factory experiment Belle II will start to record large samples of B-meson decays. The precision study of B-mesons is interesting as their decay allows for measuring the size of Charge-Parity violation and thus probe the matter and anti-matter asymmetry in particle decays. The size of Charge-Parity violation cannot be determined by a single measurement, but by the combination of several precision observables and any disagreement would be a strong indication for new physics processes beyond the Standard Model. The goal of this proposal is to carry out a precision measurement of the CKM matrix element Vub, whose absolute value is one of the important constraints in the extraction of the size of Charge-Parity violation. Experimentally Vub can be measured by studying semileptonic B-meson decays obtained by studying exclusive or inclusive hadronic final states. There is a long-standing tension between both approaches with a statistical significance of 3.4 standard deviations. One possible reason for this tension is the use of model functions to describe the b-quark motion inside the B-meson in state-of-the-art determinations using inclusive decays. To eliminate this possibility, this application proposes a coherent strategy how this functional form can be extracted simultaneously with Vub in a global analysis of measured kinematic distributions of radiative and semileptonic B-meson decays measured with the Belle II experiment. As part of the preparatory work and to establish the necessary experimental techniques a first analysis using Belle data will be carried out. The direct experimental determination of the functional form of the b-quark motion inside the B-meson will remove the model assumptions made in the state-of-the-art inclusive Vub measurements which in turn will help to shed light on the observed differences between inclusive and exclusive Vub measurements. In addition the shape function can be used to search for new physics contributions in radiative decays in a model independent way.