B介子非轻衰变中的高阶微扰和高阶幂次修正的计算及唯象研究

Thanks to the successful running of the two B factories BaBar and Belle, the theoretical and experimental studies of B physics have made great progress during the past ten years. With the running of the current LHCb and the future SuperKEKB experiments, we are entering an era of precision flavour physics, which urgently requires us to improve further the accuracy of the theoretical predictions. For this purpose, we shall carry out the following studies: ① adopting the QCD factorization approach and the soft-collinear effective theory, in combination with the analytical computational techniques of multi-loop Feynman diagrams developed in recent years, perform a systematic study of the two-loop QCD corrections in two-body hadronic B-meson decays; ② within the framework of soft-collinear effective theory and some other effective theories of QCD, make a further study of the power corrections in the collinear factorization approach and, in combination with the completion of the two-loop QCD corrections, perform a detailed phenomenological analysis of various two-body hadronic B-meson decays; ③ combining the factorization approach and the other phenomenological methods like SU(3) flavour symmetry, study systematically the three-body hadronic B-meson decays as well as the two-body hadronic D-meson decays; ④ focusing closely on the latest experimental progress and using the continuously improved theoretical tools, study various New Physics effects in the quark flavour physics. The applicant has some research foundations in the calculations of higher-order corrections and phenomenolocial studies of B-meson decays and, up to now, has published more than 30 research papers, which have been cited more than 620 times. This program will be very helpful for the precision test of the Standard Model of particle physics and the indirect searches for New Physics signals.

由于BaBar和Belle的成功运行，B物理实验和理论研究已取得很大进展。随着LHCb和下一代SuperKEKB的运行，我们正进入一个精确味物理时代，这亟需我们充分提高理论预言的精度。为此，我们将①采用QCD因子化方案和软共线有效理论，利用多圈费曼图的解析计算技术，系统计算B介子非轻衰变中的两圈QCD修正；②采用软共线有效理论和其它QCD有效理论，深入研究因子化方案下的高阶幂次修正，并结合两圈QCD修正计算结果，对B介子两体非轻衰变作全面的唯象分析；③结合因子化方案和SU(3)味对称性等唯象方法，系统研究B介子三体非轻衰变和D介子两体非轻衰变；④密切关注实验进展，利用不断完善的研究方案，系统研究重味物理中的新物理效应。申请人在B介子衰变中的高阶修正计算和唯象研究方面具有一定研究基础，已发表论文30余篇，被引用620余次。本项目对粒子物理标准模型的精确检验和新物理信号的间接寻找具有重要意义。

重味物理是粒子物理学中的重要前沿领域之一。伴随着两个B介子工厂、LHCb和Belle II的运行，实验和理论研究均取得了显著进展，我们正进入一个精确味物理时代。在本项目中，我们密切关注相关研究进展，主要开展了如下研究：①采用QCD因子化和软共线有效理论，利用多圈费曼图的解析计算技术，我们首次完整地计算了对QCD企鹅振幅的两圈QCD修正。结合已完成的对树图振幅的两圈QCD修正，这使得我们可对B介子两体非轻衰变的直接CP破坏进行次次领头阶的预言。②在b强子的“class-I”树图衰变过程中，由于只有颜色允许的树图振幅，而旁观者散射图和湮灭图是被幂次压低的，这类过程理论上相对干净。为进一步检验因子化定理，我们首次系统地计算了对这类过程的两圈QCD修正，并讨论了它们对分支比的影响。这为面向LHCb和Belle II精确测量的理论研究奠定了基础。③围绕着R(D(*))和R(K(*))反常，我们从新物理角度，采用模型无关和模型相关的办法，对它们进行了全面的唯象研究。这将有助于具体新物理模型的构建和高能量前沿新粒子的直接寻找。④针对“BaBar对τ->Ks pi nu过程CP不对称性的测量值与理论预言存在2.8σ偏差”现象，我们在模型无关和leptoquark模型下研究了该过程。我们发现，在过程的分支比和不变质量谱的联合限制下，这一反常很难得以解释。我们还指出，中性K介子混合的CP破坏会在τ->Ks pi nu过程的角分布中引起非零的CP不对称性，并预计可在Belle II上得以测量。⑤唯象上，各种变体的2HDM常被用来解释诸多的反常现象。我们发现，2HDM的汤川耦合可基于“最小味破坏”思想构造出来，并可仅由费米子的质量以及混合矩阵，以幂指数的形式进行描述，从而减少自由参数的个数，提升模型的预言性。该模型能够对R(D(*))和R(K(*))反常、中微子质量以及暗物质给出合理的解释。