Charmless B-decays in Soft-Collinear Effective Theory

b介子衰变为轻强子是检验夸克风味混合和CP违背的Cabibbo-Kobayashi-Maskawa机制的核心。在标准模型（SM）中，无魅力的b -衰变是由罕见的b -»u夸克跃迁或环诱导的b -»d/s衰变介导的，这些衰变对SM之外的新重粒子的影响很敏感。无粲B衰变的现象学非常丰富，范围从半轻子B- > X_u I nu到非轻子8 - >k pi和辐射B- >x_s γ衰变。在接下来的几年里，大多数无腔的b衰变将在大型强子对撞机和超级香料工厂Belle II上进行仔细检查。要对实验数据进行有意义的解释，就需要控制QCD中潜在的强子矩阵元素。重夸克展开（HQE）及其以有效场论（eft）形式体现的场理论为计算l/m_b和alpha_s（m_b）的双重展开中的强子矩阵元素提供了一个系统的框架。在HQE的主导功率下，强子矩阵元素分解为微扰系数函数和过程无关的强子参数。对于处于最终态的高能粒子的衰变，分解尤其重要。能量自由度阻止了局部算子积展开，留下了具有非局部强子矩阵元素的硬散射核的卷积。相关的EFT被称为软共线有效理论（SCET），人们根据物理环境来区分两种不同的版本。SCET-1是适用于包容性b衰变的EFT。微分衰减率在端点区域的因式分解是很好的。SCET-1还提供了基于重整化群（RG）技术的微扰理论中所有阶恢复对数修正的方法。目前对SCET-2中独占b衰变的理论认识尚不完整。该问题涉及到各种远程模式的分离，从而导致端点发散卷积积分。目前，人们通常试图通过将端点敏感的贡献吸收到强子参数中来绕过这个问题。虽然这样的程序限制了EFT技术的应用，但更好地理解端点动力学是可取的。该项目旨在从各个方面改进SCET技术。首先，我们将重新讨论排他性b衰变率的分解。在过去的几年中，对于对撞机物理观测的SCET-2分解定理的理解已经取得了相当大的进展。这些新技术被命名为“共线异常”和“快速RG”，该项目旨在将这些技术转化为b物理应用。此外，将研究非摄动输入参数的RG性质，并推导出新的多体最终态衰变分解定理。

B-meson decays into light hadrons play a central role in testing the Cabibbo-Kobayashi-Maskawa mechanism of quark flavour mixing and CP violation. Within the Standard Model (SM), charmless B-decays are mediated by rare b -» u quark transitions or by loop-induced b -» d/s decays that are sensitive to effects from new heavy particles beyond the SM. The phenomenology of charmless B-decays is extremely rich, ranging from semiieptonic B -> X_u I nu to nonleptonic 8 -> K pi and radiative B -> X_s gamma decays. Most of the chamnless B-decays will be scrutinized at the Large Hadron Collider and the super-flavour factory Belle II in the next few years. A meaningful interpretation of the experimental data requires to control the underlying hadronic matrix elements in QCD. The heavy quark expansion (HQE) as well as its field-theoretical incarnation in terms of effective field theories (EFTs) provide a systematic framework to compute the hadronic matrix elements in a twofold expansion in l/m_b and alpha_s(m_b). At leading power in the HQE the hadronic matrix elements factorize into perturbative coefficient functions and process-independent hadronic parameters. The factorization is particularly involved for decays with energetic particles in the final state. The energetic degrees of freedom prevent a local operator product expansion, and one Is left with convolutions of hard-scattering kernels with nonlocal hadronic matrix elements. The relevant EFT is called Soft-Collinear Effective Theory (SCET) and one distinguishes between two different versions depending on the physical context. SCET-1 is the appropriate EFT for inclusive B-decays. The factorization of the differential decay rates in the endpoint region is well established. SCET-1 also provides the means to resum logarithmic corrections to all orders in perturbation theory based on renormalization group (RG) techniques. The theoretical understanding of exclusive B-decays within SCET-2 is currently incomplete. The problem is related to the separation of the various long-distance modes which result in endpoint-divergent convolution integrals. At present, one typically tries to circumvent this problem by absorbing the endpoint-sensitive contributions into hadronic parameters. While such a procedure limits the application of the EFT techniques, a better understanding of the endpoint dynamics is desirable. The project aims at improving the SCET techniques in various respects. First, the factorization of exclusive B-decay rates will be revisited. In the last few years, there has been considerable progress in understanding SCET-2 factorization theorems for collider physics observables. The new techniques go under the names 'collinear anomaly' and 'rapidity RG', and the project aims at transfemng these techniques to B-physics applications. In addition, RG properties of nonperturbative input parameters will be investigated and new factorization theorems for decays into multi-body final states will be derived.