微扰QCD因子化和Bc介子多体衰变过程唯象研究

Driven powerfully by the Large Hadron Collider experiments, the Bc meson physics has become one of the important topics in the frontiers of flavor physics currently. The Bc meson decays can provide rich physics for investigating the heavy quark dynamics. In light of the increasingly precise data, we shall explore the Bc meson transverse-momentum-dependent wave function based on the kT factorization theorem and derive the new Sudakov factor by resumming the important logarithms in the one-loop QCD corrections, which will modify and improve the perturbative QCD factorization formalism for the Bc meson decays. Subsequently, armed with this improved framework, we shall study the multibody weak decays of Bc meson systematically and analyze the QCD behavior of the di-meson distribution amplitudes deeply in the standard model by calculating the observables such as transition form factors, branching ratios, CP violations, and polarization fractions etc., with more accuracy and reliabilities, which will provide important evidences at the theoretical aspects for analyzing plenties of data of Bc meson decays with good precision at the current Large Hadron Collider and/or the future Circular Electron-Positron Collider experiments, then exploring the perturbative and nonperturbative QCD dynamics, understanding the polarization puzzles and the mechanisms of weak annihilation decays and CP violations, and searching for the new physics beyond the standard model.

受大强子对撞机实验的强力驱动，Bc介子物理成为当前味物理前沿领域的重要研究课题之一。Bc介子弱衰变为研究重夸克动力学提供丰富的物理过程。鉴于日渐精确的实验测量，本项目拟基于kT因子化定理研究Bc介子横向动量依赖波函数，对其单圈QCD修正中的重要对数项做重求和，导出新的Sudakov因子，改进并完善Bc介子衰变的微扰QCD因子化框架。随后据此对Bc介子多体衰变过程展开系统研究，准确、可信地计算跃迁形状因子、分支比、CP破坏、极化分数等可观测量，深入研究“两介子分布振幅”的QCD行为，为唯象分析大强子对撞机及未来环形正负电子对撞机大量较高精度的Bc介子衰变数据，研究微扰和非微扰QCD动力学，理解极化疑难、湮灭衰变机制和CP破坏机制，探寻超出标准模型新物理提供重要的理论依据。

在以往的微扰QCD因子化下，粲夸克质量效应并未在kT重求和中考虑，仅是纳入硬散射核计算中，这导致B介子到粲偶素、粲介子以及Bc介子衰变的理论框架并不完整，相应的影响在Bc介子衰变中尤为显著。需要强调的是，相关理论结果对粲夸克质量的选取较为敏感。在本项目中，我们基于kT因子化定理，定义Bc介子横向动量依赖波函数(形状参数待定)，在次领头对数精度对Bc->J/\psi衰变完成了对粲夸克质量效应的kT重求和，推导得到高能量粲夸克相关联的新的Sudakov因子，改进了B到粲偶素及Bc到粲偶素衰变的微扰QCD因子化框架，也为改进b夸克介子衰变到粲介子的PQCD因子化框架做好准备。借助这一新的Sudakov因子，我们对Bc->J/\psi形状因子及Bc->J/\psi\pi衰变做了研究，且在B->J/\psi f0, J/\psi f1, \etac (P,V)等过程中检验了其所带来的影响。结果证实Bc->J/\psi\pi分支比有高达10%-20%的增强。与此同时，为了在Bc介子衰变顺利展开多体研究，我们首先利用丰富的B介子三体衰变数据，对\pi\pi和KK等两介子分布振幅做了唯象探究和限制，为在改进的微扰QCD因子化方案下对Bc介子多体衰变做出更为精确的理论预言奠定基础，并为未来Bc介子衰变的精确实验探测和发现超出标准模型新物理提供理论指导。