Hadronic Vacuum Polarisation Contributions to g-2 and other precision observables

强子真空偏振对 g-2 和其他精密可观测物体的贡献

• 批准号: 2890876
• 金额: --
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2890876
• 关键词: Hadronic; Vacuum; Polarisation; Contributions; other

Sustained tension between the measured results of the Muon g-2 experiment at Fermilab and the theoretical prediction suggests a potential for new physics beyond the Standard Model. The precision of the Fermilab measurement has been improved by a factor of two by analysis of Run 2 and Run 3 data, and is expected to improve by the same factor again once all of the data collected has been analysed. This improvement in experimental accuracy needs to be accompanied by a comparable improvement in theoretical accuracy.The largest source of uncertainty on the theoretical prediction comes from the Hadronic Vacuum Polarisation (HVP) contribution. While other contributions to the prediction can be calculated within the framework of perturbation theory, the HVP contribution must be calculated from dispersive or lattice QCD methods. The primary focus of this PhD is to refine the dispersive calculation of the HVP contribution, by means of developing improved methodology and including new data sets not previously available.Among the new data sets to be considered is the n+n- data collected with the CMD-3 experiment. There is a considerable discrepancy between these results and those obtained previously by other experiments including CMD-2, which ran at the same facility. It will be necessary to determine the best way to include these data alongside prior results with which they seem incompatible.There also exists a notable tension between the dispersive and lattice QCD predictions for the HVP contribution to g-2. When lattice QCD is used to perform the HVP calculation, a result more consistent with the experimental result is obtained. The source of this tension is as yet unknown, and is the source of much investigation. As part of this project, dispersive predictions of so-called window observables can be made and compared to those of lattice QCD groups.The first stage of this project will be to update the program used for the KNT calculation of the HVP contribution into a more modern language. This will allow use of powerful modern software features such as relational databases and make the code more accessible. Blinding procedures will also be implemented into the calculation from the start; these are introduced with the aim of avoiding biasing the final result.As the project progresses, the statistical methods used in the code will be refined with the aim of assigning more accurate uncertainties. The role of systematic uncertainties and correlations will also be scrutinised. New data sets will be introduced into the analysis, further increasing the precision and accuracy of the measurement. Unbiased methods of reconciling data sets in tension will be developed and applied to address outstanding potential issues. Furthermore, the handling of radiative corrections in the analysis will be improved.The project will yield not only an updated dispersive calculation of the HVP contribution to g-2, but also updated values for other precision observables. These can be compared to the results of other precision physics experiments (such as the hyperfine splitting of muonium), or, in the case of the calculation of the running of the QCD coupling, used as inputs for further measurements. The results of the updated calculation will be compared to the final Fermilab measurement and results from lattice QCD. This project therefore will make a potentially important contribution to a major test of the Standard Model and the search for new physics.

在Fermilab的MUON G-2实验的测量结果和理论预测之间的持续张力表明，超出标准模型以外的新物理学的潜力。通过分析运行2和运行3个数据，Fermilab测量的精度已通过2倍提高了两倍，并且一旦分析了所有收集的数据，预计将再次提高相同的因素。实验准确性的这种提高需要伴随理论准确性的可比性提高。理论预测的最大不确定性来源来自Hadronic真空极化（HVP）的贡献。尽管可以在扰动理论的框架内计算对预测的其他贡献，但HVP贡献必须根据分散或晶格QCD方法计算。该博士学位的主要重点是通过开发改进的方法来完善HVP贡献的色散计算，并包括以前不可用的新数据集。在要考虑的新数据集中是使用CMD-3实验收集的N+N数据。这些结果与先前由包括CMD-2在内的其他实验获得的结果之间存在很大差异，这些实验在同一设施上运行。必须确定将这些数据纳入这些数据的最佳方法以及它们看起来不兼容的先前结果。还存在分散性和晶格QCD预测HVP对G-2的贡献之间的显着张力。当使用晶格QCD执行HVP计算时，结果将与实验结果更一致。这种张力的根源尚不清楚，并且是大量调查的根源。作为该项目的一部分，可以对所谓的窗口可观察物进行分散预测，并将其与lattice QCD组的分散预测。该项目的第一阶段是更新用于KNT计算HVP贡献的程序为更现代的语言。这将允许使用强大的现代软件功能，例如关系数据库，并使代码更容易访问。从一开始，盲目程序也将在计算中实施；这些引入的目的是避免偏向最终结果。随着项目的进行，代码中使用的统计方法将进行完善，目的是为了分配更准确的不确定性。系统的不确定性和相关性的作用也将受到审查。新的数据集将引入分析中，进一步提高了测量的精度和准确性。将开发并应用无偏见的张力数据集的方法，以解决未来的潜在问题。此外，将改进分析中辐射校正的处理。项目不仅会产生对G-2贡献的更新分散计算，还将为其他精确观察值提供更新的值。这些可以与其他精度物理实验（例如Muonium的超精细分裂）的结果进行比较，或者在计算QCD耦合的运行情况下，用作进一步测量的输入。更新计算的结果将与最终的Fermilab测量和晶格QCD进行比较。因此，该项目将对标准模型的重大测试和寻找新物理学做出潜在的重要贡献。