B介子及重子弱衰变中新物理唯象研究

发布时间：2018-08-03 08:13

【摘要】：粒子物理的标准模型(Standard Model,SM)已经被证明是描述强相互作用、电磁相互作用以及弱相互作用的最好理论,它的预言几乎能经受住所有实验的检验,尤其是Higgs玻色子的发现。然而,标准模型并不完美,虽然能给电弱对称性破缺以合理的解释——Higgs机制,但是负责电弱对称性破缺的标量二重态是否只有一个尚未明确。另外,实验上也存在一些与标准模型预言有偏离的观测量,如R(D(*)),RK等,这些问题的存在,为新物理(New Physics,NP)留下了一定的空间。对新物理的探索,一方面可以从高能量的实验直接寻找新物理信号,如欧洲的大型强子对撞机(Large Hadron Collider,LHC);另一方面可以通过高亮度的精确味物理研究间接探测新物理,尤其对b味物理的研究,是非常有效的手段,因为低能量区域,虽然不能直接产生新粒子,新物理却可以通过圈图对低能味物理过程产生修正,可以探测到很高能量标度下的新物理迹象。本文主要研究两种新物理模型在B介子衰变,中性B介子混合以及∧b重子衰变中的唯象效应,其中一种新物理是双Higgs二重态模型(Two Higgs Doublet Model,2HDM),具体是指最小味破坏(Minimal Flavor Violation,MFV)假设下的色八重态2HDM;另一种是Leptoquark(LQ)模型,具体包括标量和矢量两种情形。首先,我们分别在第一和第二章中介绍了 B物理研究的意义及进展,及其理论基础;然后,在第三章中介绍了色八重态2HDM,我们系统计算了Bs,d0-Bs,d0混合中的观测量△Ms,d,并且与通常计算不同的是,我们考虑了外线b夸克的质量和动量;我们还详细计算了纯轻衰变Bs,d→μ+μ-过程中的平均时间积分分支比B(Bs,d→μ++μ-),综合考虑Z → bb,辐射衰变B→Xsγ以及B→K*(ρ)γ过程,我们对该2HDM的参数进行联合限制。我们发现,这些过程对Yukawa耦合系数ηu的限制很强,而对另一个Yukawa耦合ηd则基本无限制,对Higgs势中的参数λ1也无任何限制;另外,B介子的遍举和单举辐射衰变过程与其他所考虑过程对NP参数的依赖关系不同,可以提供补充信息。标量和矢量LQ模型都可以解释遍举半轻衰变B→D(*)τντ 过程中物理量R(D(*))的反常,在第四、五两章我们分别讨论了这两种LQ模型在B介子和Ab重子弱衰变中的唯象效应。第四章中,我们首先通过对Bc介子的纯轻衰变Bc-→τ-ντ排除掉标量LQ模型中的两组解,进而考察剩余的两组解对辐射衰变Bc→ τντγ、遍举半轻衰变B→D(*)τντ以及单举半轻衰变B→Xcτντ过程中观测量的影响。我们发现标量LQ模型剩余两组解几乎对所有观测量,除D*介子和τ轻子的纵向极化和轻子的前后不对称以外,相对标准模型的预言都有一定的增强,而这两组解之间是很难进行唯象区分的。第五章中,我们考察这两种LQ模型对同是由b→ Cτντ夸克层次跃迁过程诱导的Ab重子衰变∧b→∧cτντ过程的影响,我们发现这两种LQ模型对该过程几乎所有观测量,除∧c重子和τ轻子的纵向极化以外,相对SM的预言都有几乎相同的增强,因此这两种LQ模型无法区分开来,另外每种LQ模型的两组解之间也无法通过该半轻衰变过程进行区分。理论上,随着格点(Lattice)QCD的发展,与低能区强相互作用相关的非微扰参数可以更加精确地计算,很多B物理过程将会得到更可靠的预言。实验上,正在运行的LHC,以及将来的超级B工厂SuperKEKB,积分亮度都会有很大的提高,可以提供更多B介子的产生和衰变事例数,为B物理的研究提供了良好的发展前景。
[Abstract]:The standard model of particle physics (Standard Model, SM) has been proved to be the best theory to describe the strong interaction, the electromagnetic interaction and the weak interaction. Its prediction can almost withstand the test of all the experiments, especially the discovery of the Higgs boson. However, the standard model is not perfect, although it can break the weak symmetry of electricity. Rational explanation - Higgs mechanism, but only one of the scalar duality states responsible for the weak symmetry of electricity is not yet clear. In addition, there are some experimental observations that deviate from the prediction of the standard model, such as R (D (*)), RK and so on. These problems have left a certain space for the new physics (New Physics, NP) and the exploration of new physics. On the one hand, we can find new physical signals directly from high energy experiments, such as the large Large Hadron Collider (LHC) in Europe; on the other hand, it can be used to detect new physics indirectly through high luminance and accurate physical research, especially for the study of B physics, because low energy regions, though not directly, are not direct. New physics can be used to modify the physical process of low energy taste through a circle graph, which can detect new physical signs under high energy scale. This paper mainly studies the phenomenological effect of two new physical models in B meson decay, neutral B meson mixing and a B baryon decay. One of the new physics is double Higgs duality mode Two Higgs Doublet Model (2HDM) refers to the color eight gravity 2HDM under the hypothesis of minimum flavor (Minimal Flavor Violation, MFV); the other is Leptoquark (LQ) model, including two cases of scalar and vector. First, we introduce the significance and progress of the physics research in the first and the second Zhang Zhong, and the theoretical basis; Then, in the third chapter, the color eight gravity 2HDM is introduced. We systematically calculate the observable measurements of Bs, d0-Bs, and d0, Delta Ms, D, and, unlike the usual calculations, we consider the mass and momentum of the exterior line B quarks, and we have also calculated the average time integral branch of the pure light decay Bs and D to Mu + in the process of B (Bs, D to + + +). Considering the Z to BB, the radiation decay B to Xs gamma and B to K* (rho) gamma processes, we have a joint restriction on the parameters of the 2HDM. We find that these processes have a strong restriction on the Yukawa coupling coefficient ETA u, while the other Yukawa coupling ETA D is basically unrestricted, and there is no restriction on the number of the parameters in the Higgs potential. In addition, the multiplication and single lifting of the BB mesons are not limited. The process of radiation decay is different from the dependence of other considered processes on NP parameters, which can provide additional information. The scalar and vector LQ models can all explain the anomaly of the physical quantities R (D (*)) of the semi light decay B to D (*) tau (*). In the fourth and 52 chapters, we discuss the weak decay of the two LQ models in B mesons and Ab barons. The phenomenological effect. In the fourth chapter, we first examine the two sets of solutions in the scalar LQ model by removing the pure light decay of the Bc meson Bc- - tau - V, and then investigate the influence of the remaining two groups of solutions on the radiation decay Bc, tau [v], the half light decay B to D (*) tau [*], and the single lift half light decay B to Xc tau tau. We find the scalar LQ The remaining two sets of solutions of the model are almost all measured. Except for the longitudinal polarization of the D* meson and Tau Lepton and the asymmetry between the leptons and the leptons, the predictions of the relative standard models have a certain enhancement, and the two groups of solutions are difficult to make a phenomenological distinction. In the fifth chapter, we examine these two LQ models to be the same as from the B to C tau Tau The effect of the decay of the Ab baryon decay in the process of the decay of the Ab baryon - B - A - C tau, we find that these two LQ models have almost all the observations of the process, except the longitudinal polarization of the C baryon and Tau Lepton, and the predictions of the relative SM are almost the same, so the two LQ models are separated from the two groups of each LQ model. In theory, with the development of the Lattice QCD, the non perturbative parameters related to the strong interaction of the low energy region can be more accurately calculated, and many B physical processes will be predicted more reliably. In the experiment, the LHC, and the future super B factory SuperKEKB, will be brighter. Degree will be greatly improved, which can provide more examples of the production and decay of B mesons, and provide a good prospect for the study of B physics.
【学位授予单位】：华中师范大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O572.2

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