The Flavour Anomalies: Fluke, Fallacy or New Physics?

粒子物理学的标准模型代表了我们目前对构成宇宙的基本粒子以及控制它们的相互作用（力）的最佳认识。尽管到目前为止，大多数基本粒子的行为都与标准模型所预测的一致，但宇宙学观测告诉我们，标准模型不可能是全貌。例如，在标准模型中，物质和反物质是彼此近乎完美的镜像。然而，我们宇宙中物质的主导地位告诉我们，一定有一些，到目前为止未知的，相互作用打破了这种物质，即反物质对称。LHCb实验是位于欧洲核子研究中心大型强子对撞机（LHC）上的四个实验之一。它被设计用来精确测量一种叫做美夸克的粒子。这个奖项的重点是对标准模型中非常隐蔽的b-夸克衰变的研究。通过精确测量这些罕见过程发生的速率，我们可以推断出标准模型中没有描述的新相互作用的存在。近年来，对这些罕见的b衰变的测量显示出与标准模型预测的偏差。这个奖项将进一步加深我们对导致这些异常现象的原因的理解，目的是确定它们的起源是否可能是大型强子对撞机超越标准模型过程的第一个迹象。该项目的PI是LHCb合作中的Laura Bassi倡议的创始人，该倡议汇集了对解决粒子物理学中的性别和多样性问题感兴趣的早期职业研究人员。这笔拨款将支持PI在这一领域的继续工作。然而，在罕见的b-衰变中观测到的张力相对于标准模型可以超过5个标准差，这些偏差可能是由于对非局部强子效应的理论描述不佳，而非局部强子效应不能从标准模型的第一原理中推导出来。该奖项对B^0→K^(*0) μ+μ-衰变中的非局部强子效应进行了新颖的数据驱动测量，为风味异常之谜提供了关键部分。通过B^0→K^(*0) [τ^+ τ^-→μ^+μ-]的衰变，用类似的方法测量了非局部陶子对B^0→K^(*0) μ^+μ ^-的贡献。该方法对B（B^0→K^(*0) τ^+ τ^-）的期望灵敏度达到世界领先水平。b→stτ ^+ τ^-的测量对于理解这些异常是至关重要的，因为受欢迎的新物理解释预测了这些模式的大幅增强。该项目还将对B^0→K^(*0) μ+μ-中潜在有效耦合的假想贡献进行首次拟合，所提出的方法将导致B→sl+l-衰变中cp违反约束的数量级改进。鉴于风味异常，这种测量是有趣的，因为超越sm的CP违反的约束是理解宇宙中物质对反物质的主导地位的核心。该项目还将委托并验证LHCb升级I探测器的性能，该探测器将首次在LHC运行3（2022-2026）期间获取数据。这项调试工作将成为后续使用Run 3数据测量b→sμ^+ μ^-过程的基础，这也是该项目的一部分。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Standard Model of particle physics represents our best current knowledge of the fundamental particles that make up our universe and the interactions (forces) that govern them. Although to date most fundamental particles have been observed to behave as predicted by the Standard Model, cosmological observations tell us that the Standard Model cannot be the complete picture. For example, in the Standard Model, matter and anti-matter are a near-perfect mirror of each other. However, the dominance of matter in our universe tells us that there must be some, as of yet unknown, interaction breaking this matter, anti-matter symmetry. The LHCb experiment is one of the four experiments situated on the Large Hadron Collider (LHC) at CERN. It is designed to make precision measurements of a particle called a beauty (b) quark. This award focuses on the study of b-quark decays which are very suppressed in the Standard Model. By precisely measuring the rates at which these rare processes happen, we can infer the existence of new interactions, not described within the Standard Model. Over recent years, measurements of these rare b decays have shown deviations with Standard Model predictions. This award will further our understanding behind what is causing these anomalies, with the goal of determining whether their origin could be the first sign of a beyond-the-Standard-Model process at the LHC. The PI of this project is the founder of the Laura Bassi initiative within the LHCb collaboration, which brings together early career researchers interested in tackling issues of gender and diversity within particle physics. This grant will support the PI’s continued work in this area.Whereas the tensions observed in rare b-decays can be over 5 standard deviations with respect to the Standard Model, these deviations could be due to poor theoretical descriptions of non-local hadronic effects, which cannot be derived from first principles in the Standard Model. This award performs a novel data-driven measurement of non-local hadronic effects in the decay B^0→K^(*0) μ+μ-, providing a crucial part of the flavour-anomaly puzzle. Similar methods are used to measure non-local tauonic contributions to B^0→K^(*0) μ^+ μ^-, via the decay B^0→K^(*0) [τ^+ τ^-→μ^+μ- ]. The expected sensitivity on B(B^0→K^(*0) τ^+ τ^- ) obtained using this method is world-leading. Measurements of b→sτ^+ τ^- are critical to understanding the anomalies, as favored new physics explanations predict large enhancements in theses modes. This project will also perform the first fit for the imaginary contributions to the underlying effective couplings in B^0→K^(*0) μ+μ- , with the proposed method resulting in an order-of-magnitude improvement on CP-violation constraints in b→sl+l- decays. This measurement is interesting in light of the flavor anomalies, and because constraints on beyond-the-SM CP violation are central to understanding the dominance of matter over anti-matter in the universe. This project will also commission and validate the performance of the LHCb Upgrade I detector, which takes data during the LHC Run 3 (2022-2026) for the first time. This commissioning work will be the cornerstone of subsequent measurements of b→sμ^+ μ^-processes using Run 3 data, which are also performed as part of this project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.