Precision Tests of the Standard Model and Low Energy Hadronic Interactions

标准模型和低能强子相互作用的精度测试

• 批准号: SAPIN-2016-00037
• 负责人: Aleksejevs, Aleksandrs
• 金额: $ 1.68万
• 依托单位: Memorial University of Newfoundland
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=718420
• 关键词: Precision; Tests; Standard; Model; Low

Search for physics beyond the Standard Model (BSM) has three major directions: energy, cosmic and precision frontiers. I am interested in the precision frontier driven by the indirect searches, where new particles could impact observables such as scattering cross section or asymmetry causing small deviations from original Standard Model (SM) predictions, and there are several upcoming new-generation, ultra-precise measurements with intense particle beams which could detect such small effect. One of such experiments, MOLLER, studying parity-violating Møller scattering, would allow a determination of the weak mixing angle with an uncertainty of 0.1%, an improvement of a factor of five in fractional precision compared with the previous E-158 measurement. At such precision, any inconsistency with the SM could signal BSM physics. Such precision will require a matching theoretical uncertainty, which can be achieved only by including electroweak calculations up to the two-loop order. We plan to construct Two-Loop Electroweak Computational Model (2L-ECM) for the particles of the Standard Model and calculate the full set of two-loop contributions to the Parity Violating (PV) asymmetry for electron-electron scattering required by the MOLLER experiment. Later, 2L-ECM should be extended to the broad spectrum of processes involving particles of SM. The next stage would be including the various hypothetical BSM particles up to one-loop level, and studying their impact on the electroweak observables. The second direction of my research program is in the Chiral Perturbation Theory (ChPT), which has been tremendously successful in describing low-energy hadronic properties in the non-perturbative regime of QCD. Some of the major goals of the low-energy QCD are the study of hadronic form factors, which reflect the static structure, and the investigation of the dynamical hadronic response to the external electromagnetic field via electric and magnetic polarizabilities. To study the dependence of the electric and magnetic polarizabilities on the photon energy, we used the relativistic ChPT while applying the multipole expansion approach for the Compton structure functions. Previously, we have developed the Computational Hadronic Model (CHM) based on relativistic ChPT, which operates up to one-loop expansion. The advantage of this model is that it allows avoiding various approximations in the calculations and retaining all the possible degrees of freedom arising from the SU(3) chiral Lagrangian. The next logical step would be to upgrade the CHM to two-loops. Based on the work from 2L-ECM, we plan to develop the Two-Loop Computational Hadronic Models (2L-CHM), which would allow us to extend our understanding of both static (formfactors) and dynamic (polarizabilities) structure of hadrons.

对标准模型（BSM）之外的物理学的研究有三个主要方向：能量、宇宙和精确前沿。我对间接搜索驱动的精度前沿感兴趣，新粒子可能会影响可观测值，如散射截面或不对称性，导致与原始标准模型（SM）预测的微小偏差，并且有几个即将到来的新一代超精确测量，可以检测到这种微小的影响。其中一个实验，MOLLER，研究宇称违反穆勒散射，将允许确定弱混合角的不确定性为0.1%，与以前的E-158测量相比，分数精度提高了五倍。在这样的精度下，任何与SM不一致的地方都可能是BSM物理学的信号。这样的精度将需要一个匹配的理论不确定性，这只能通过包括电弱计算达到两个回路的顺序。我们计划为标准模型的粒子构建双环电弱计算模型（2L-ECM），并计算MOLLER实验所需的电子-电子散射的宇称破坏（PV）不对称性的全套双环贡献。后来，2L-ECM应该扩展到涉及SM颗粒的广泛过程。下一个阶段将包括各种假设的BSM粒子到一圈水平，并研究它们对电弱可观测量的影响。 我的研究计划的第二个方向是手征微扰理论（ChPT），它在描述QCD非微扰区域的低能强子性质方面取得了巨大的成功。低能QCD的一些主要目标是研究反映静态结构的强子形状因子，以及通过电和磁极化率研究强子对外部电磁场的动态响应。为了研究电磁极化率对光子能量的依赖性，我们使用相对论ChPT，同时应用多极展开方法的康普顿结构函数。在此之前，我们已经开发了计算强子模型（CHM）的基础上相对论ChPT，其中操作到一个循环的扩展。这个模型的优点是它可以避免计算中的各种近似，并保留了SU（3）手征拉格朗日量产生的所有可能的自由度。下一个合乎逻辑的步骤是将CHM升级为两个环路。基于2L-ECM的工作，我们计划发展双圈计算强子模型（2L-CHM），这将使我们能够扩展我们对强子静态（形状因子）和动态（极化率）结构的理解。