重味b介子非轻弱衰变的唯象学研究

Studies on nonleptonic weak decays of heavy b-flavored mesons, composed of heavy b quark and a lighter u, d, s or c quark, play very important roles in testing the theory of standard model, investigating the scheme of CP-violating asymmetries, and exploring the signals of exotic new physics. Strongly pushed by B factories(BaBar and Belle) and LHC(Large Hadron Collider) experiments, heavy flavor b physics becomes one of the very important frontiers in elemetary particle physics. It is the fact that the mechanism of annihilation decays of heavy b-flavored mesons needs understanding in depth and the QCD dynamics of light p-wave mesons such as the inner structure requires further investigation. Experimentally, besides plenties of decay modes of B meson, more and more decay events of Bs and Bc meosns will also be rapidly produced in the near future. Presently, large amounts of decay channels of heavy b-flavored mesons to two final state hadrons(e.g. light s-wave and p-wave mesons) have been detected, while the predictions on relevant physical quantities of these processes generally suffer from a few of theoretical uncertainties, which originate mainly from the evaluations of relevant hadronic matrix elements. As is well known that the perturbative QCD(pQCD) factorization approach has been employed extensively to treat the two-body hadronic decays of heavy b-flavored mesons because of the distinct advantages in smearing the endpoint singularities, then making the spectator scattering and annihilation diagrams perturbatively calculable, and remarkable successes in phenomenological analysis combined with the experimental measurements. In view of these interesting facts, the contents of this project are as follows: Within the framework of pQCD factorization approach, we will make systematic studies on the nonleptonic weak decays of heavy b-flavored mesons in the standard model through calculating the physical observables, e.g. Branching Ratios, CP-violating Asymmetries, etc., which are expected to open a new window to explore the internal structure of light p-wave mesons, and provide the theoretical supports for phenomenologically analyzing the experimental data on heavy b-flavored mesons and deeply understanding the annihilation decay mechanism in heavy flavor b physics.

重味b介子的非轻弱衰变研究对检验标准模型理论、研究CP破坏机制及探寻新物理信号有着非常重要的科学意义。在B工厂实验及LHC实验的强劲推动下，重味b物理成为最重要的前沿研究领域之一。重味b介子湮灭衰变机制有待深刻理解，p-波轻介子内部结构等QCD问题还需进一步探究。除大量B介子衰变道外，实验还将观测到更多的Bs和Bc衰变事例。重味b介子到两个末态强子的衰变过程，其理论误差主要来源于相关强子矩阵元的计算。pQCD因子化方法在解决端点发散，计算旁观者夸克图和湮灭图方面有明显的优势，并在唯象分析方面取得了显著成功。鉴于此，本项目研究内容为：基于pQCD因子化理论框架，在标准模型中，对重味b介子的非轻弱衰变过程进行系统研究，计算分支比和CP破坏等可观测物理量，为探索p-波轻介子内部结构提供新的场所，为唯象分析重味b介子实验数据并深刻理解重味b物理中的湮灭衰变机制提供理论支持。

课题组对重味b介子的部分非轻弱衰变过程在标准模型中应用pQCD因子化方法进行了细致的研究，完成了本项目的主要研究内容。经过三年的努力，我们获得如下主要研究成果：(1)通过考虑横向动量依赖的强子波函数及普适的Glauber因子演化效应对著名的“B\to \pi \pi, K\pi”疑难进行了细致研究，结果显示在新的QCD机制下以上疑难可以解决；对B \to J/\Psi V过程做了次领头阶的系统研究，对分支比、极化分数、CP破坏以及相对相位做了细致的理论预言，并讨论了企鹅图贡献对抽取B_s-\bar B_s混合相位的影响；通过对B_{(s)} \to VV过程的更新研究，我们对最新的相关实验测量做出解释，强调湮灭企鹅图和不可因子化旁观者夸克图贡献对理解极化反常相当重要，同时指出仍有待解决的问题。(2)在领头阶下对含有p-波轴矢量介子a_1(1260)、b_1(1235)、K_1(1270)、K_1(1400)、f_1(1285)、f_1(1420)的相关AP、AV、AA衰变过程进行了研究，并做了唯象分析，相关理论预言结合精确实验测量将有助于探索轴矢量介子及相应过程所包含的QCD动力学，为分析极化疑难、湮灭衰变机制等问题提供了更多的理论支持。(3)基于两夸克模型假设，对含有p-波标量介子a_0(980)、K_0^*(1430)的相关SS、SV衰变过程进行了领头阶研究，实验对相关预言的验证有助于甄别标量介子的夸克组份，研究其内部结构及相关QCD动力学。(4)对当前B_c介子非轻衰变研究的实验和理论现状进行综述，为进一步实施B_c物理研究提供较为详细的分析。我们意识到需要与pQCD因子化自洽的k_T相关的B_c介子波函数才能对未来更为精确的实验测量做出可信的物理唯象分析和可靠的理论指导。.. 获得资助以来，已在“Phys.Rev.D”、“J.Phys.G”等“SCI”源期刊发表学术论文10篇，已接受待发表论文2篇(J.Phys.G-101020，Phys.Rev.D-DL11780)，国内学术会议报告5次。相关学术论文已被国内外学术同行他人引用近50次。培养硕士生3人。