Charmless B-decays in Soft-Collinear Effective Theory

软共线有效理论中的无魅力 B 衰变

• 批准号: 290250930
• 负责人: Professor Dr. Guido Bell
• 金额: --
• 依托单位: Arbeitsgruppe Theoretische Physik 1 (Elementarteilchenphysik)
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/290250930?language=en
• 关键词: Charmless; decays; Soft; Collinear; Effective

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.

B介子衰变为轻强子在检验夸克味混合和CP破坏的Cabibbo-Kobayashi-Maskawa机制中起着核心作用。在标准模型（SM）中，无粲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衰变的现象极为丰富，从半轻子B -> X_u I nu到非轻子8 -> K π和辐射B -> X_s γ衰变。未来几年，大多数无腔B衰变将在大型强子对撞机和超级香料工厂贝儿II进行详细检查。一个有意义的解释实验数据需要控制在QCD的强子矩阵元。重夸克展开式（HQE）及其在场论上的有效场论（EFT）为计算强子矩阵元在l/m_B和alpha_s（m_B）中的双重展开提供了一个系统的框架。在HQE的主导功率的强子矩阵元分解成微扰系数函数和过程无关的强子参数。因式分解特别适用于高能粒子处于末态的衰变。的能量自由度，防止当地运营商的产品扩展，和一个是留下的卷积的硬散射内核与非本地强子矩阵元素。相关的EFT被称为软共线有效理论（SCET），并根据物理环境区分两个不同的版本。SCET-1是适用于包容性B衰变的EFT。在端点区域的微分衰减率的因式分解是很好的建立。SCET-1还提供了基于重整化群（RG）技术的微扰理论中恢复所有阶数的对数校正的方法。目前，对SCET-2中B衰变的理论认识还不完全。这个问题涉及到分离的各种长距离模式，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贡献吸收到强子参数中来规避这个问题。虽然这样的程序限制了EFT技术的应用，但需要更好地理解端点动态。该项目旨在从各个方面改进SCET技术。首先，将重新讨论排他性B衰变率的因式分解。在过去的几年里，在理解对撞机物理观测量的SCET-2因式分解定理方面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移到B物理应用中。此外，RG性质的非微扰输入参数将被调查和新的分解定理衰变到多体最终状态将被导出。