The Flavour Anomalies: Fluke, Fallacy or New Physics?

粒子物理学的标准模型代表了我们对构成宇宙的基本粒子以及支配它们的相互作用(力)的最新知识。尽管到目前为止，大多数基本粒子都观察到了标准模型所预测的行为，但宇宙学观察告诉我们，标准模型不可能是全部情况。例如，在标准模型中，物质和反物质是彼此近乎完美的镜子。然而，物质在我们宇宙中的主导地位告诉我们，一定有某种未知的相互作用打破了这种物质，反物质对称性。LHCb实验是欧洲核子研究中心大型强子对撞机(LHC)上的四个实验之一。它的设计目的是对一种被称为美(B)夸克的粒子进行精确测量。该奖项的重点是研究b夸克衰变，这种衰变在标准模型中受到了很大的抑制。通过精确测量这些罕见过程的发生速度，我们可以推断存在标准模型中没有描述的新的相互作用。近年来，对这些罕见的b衰变的测量已经显示出与标准模型预测的偏差。这项裁决将进一步加深我们对这些异常现象背后原因的理解，目的是确定它们的起源是否可能是大型强子对撞机超标准模型过程的第一个迹象。该项目的PI是LHCB合作项目中Laura Bassi倡议的创始人，该项目将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聚集在一起。这笔赠款将支持PI在这一领域的继续工作。在罕见的b衰变中观察到的张力可能超过标准模型的5个标准偏差，这些偏差可能是由于对非局域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得到。该奖项对衰变B^0→K^(*0)μ+μ-中的非局域强子效应进行了一种新颖的数据驱动测量，提供了味道反常之谜的关键部分。类似的方法也被用来通过衰变B^0→K^(*0)[μ^+μ-]来测量非局域色子对B^0→K^(*0)τ^+τ^-→μ^+μ^-的贡献。用这种方法得到的B(B^0→K^(*0)τ^+τ^-)的预期灵敏度是世界领先的。B→Sτ^+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这些模式会有很大的增强。这个项目还将对B^0→K^(*0)μ+μ-中的基础有效耦合的虚贡献进行第一次拟合，所提出的方法将导致b→s1+L-衰变中CP破坏约束的数量级改进。鉴于味道反常，这种测量是有趣的，因为对Beyond-the-The-SM CP破坏的限制是理解宇宙中物质对反物质的主导地位的核心。该项目还将调试和验证大型强子对撞机升级I探测器的性能，该探测器首次在大型强子对撞机第三次运行期间(2022-2026年)获取数据。这项调试工作将是后续使用Run 3数据测量b→Sμ^+μ^过程的基石，该过程也是作为本项目的一部分进行的。该奖项反映了美国国家科学基金会的法定使命，并已通过使用基金会的智力优势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.