高激发态重介子的产生与衰变研究

发布时间：2018-04-15 20:11

  本文选题：Bethe-Salpeter方法 + D波粲介子　； 参考：《哈尔滨工业大学》2017年博士论文

【摘要】：在近年来,Belle,BaBar以及LHCb实验组发现了大量的轨道和径向激发态重介子,在理论上对这些粒子进行分类是进一步研究的基础。与此同时,仍然有大量在理论模型中预言的高激发态重介子,尚未被实验探测到,因此计算其在特定衰变道的产率,对于实验上寻找这些高激发态粒子具有重要的参考意义。在本文中,基于Bethe-Salpeter方法以及Cornell模型,我们研究了D波粲介子在Bq(=d,s,c)衰变中的产生,以及实验中所发现的激发态1-粲介子的强衰变性质。在本文中,我们首先利用BS方法计算Bc介子到D波粲偶素的半轻与非轻衰变,即η_(c2)(1~1D_2),Ψ2(13D2),和Ψ3(13D3)。Bc介子是唯一的由两个重夸克所组成的开味基态重介子,因而只能弱衰变,目前理论中对其衰变到D波粲偶素的研究非常匮乏。而当前实验中发现的Ψ2(3823)极有可能为13D2态粲偶素,而另外两个D波的η_(c2)(1~1D_2)和Ψ3(13D3)目前仍没有被探测到;同时,由于夸克模型理论估计1~1D_2,33D2以及13D3态粲偶素质量都在DD*阈值附近,导致其宽度非常窄,有利于在实验中被观测到。在我们的计算中,利用BS方法计算的强子跃迁矩阵元,能够有效的包含对于高激发态非常重要的相对论修正。我们的计算结果表明,在Bc衰变中D波粲偶素的产生分支比可达到10-4量级,已经到达到当前LHC B工厂的探测阈值,在未来的实验中将有很大的几率发现这些D波粲偶素粒子。另一方面,BaBar与LHCb实验组也在近年来发现一批激发态的开味粲介子,其中有可能的2-态D2以及3态的D(s)3*等D波介子,而其它的D波D(s)介子仍然没有被探测到。因此,在理论上对这些D波重轻介子在相应的Bq(q=d,s,c)介子衰变中的产生问题进行系统性研究,对于理论和实验都具有重要的参考意义,这些内容也是本文的一个重要研究课题。我们利用Salpeter波函数求解相应过程的强子弱衰变矩阵元,同时给出了一些实验中的可观测物理量,如半轻衰变中的前后不对称度AFB,带电轻子动量和角度分布谱,以及半轻和非轻衰变的宽度与分支比。我们的结果表明D波D(s)介子在相应的B(s)衰变中的分支比可以到10-3量级,而Bc到D波D介子的半电子衰变分支比在10-5量级。另外,对于2-态粒子,D2和D1',其为1D2-3D2的混合态粒子,我们给出其半轻衰变宽度随混合角变化的分布。同时,为了本研究的完整起见,我们也计算了Bc到D波Bd,s介子的半轻与非轻衰变。与此同时,在近年来的实验中,也发现了一些可能的量子数为1-的激发态粲介子,包括 D_(s1)*(2700)+,D_(s1)*(2860)+,D*(2600)0,D*(2650)0,D_1*(2680)0 和D1(2760)0。对这两个D_(s1)*介子的研究中,人们发现其属性与理论预言的2S和1D态介子存在一定的偏差,难以用简单的2S+1LJ对其进行分类识别;而在传统的夸克模型下,上述4个D介子应该对应着两个激发态的1-粲介子,目前实验探测的不一致也对其识别造成很大的困扰。在本文的研究中,我们利用BS方程以及PCAC关系对这些潜在的1-粲介子主要的强衰变属性予以系统性研究。我们的结果揭示,这两个1-态Ds介子可以在23S1-13D1混合机制下,用一个小的混合角很好的解释。而D*(2600)0同样可以在这种混合机制下,被解释为23S1主导的态;对于D*(2650)0和D_1*(2680)0,在2S和1D两种不同的识别下,我们的得到的总宽度同实验结果都没有巨大的冲突,如果考虑到夸克模型预言的质量区间,其更有可能对应着23S1态粲介子;对于LHCb发现的D1(2760)0,如果将其识别为13D1态粒子,我们计算得到的总宽度比实验测量大了 100 MeV。同时我们给出了和其他理论结果的对比,以及几个比较重要的衰变宽度的比率。对于这些1-态D介子的识别,更进一步的实验测量信息是很有必要的,如衰变比率Γ(Dn)/Γ(D*n)。
[Abstract]:In recent years, Belle, BaBar and LHCb experimental group found a large number of orbital and radial excited heavy meson, the theory of the particle classification is the basis for further research. At the same time, there are still a lot in the theoretical model predicts high excited heavy meson, has not yet been experimentally detected, so the calculation of the the specific channel yield, these high excited particles have important reference significance for the experimental finding. In this paper, the Bethe-Salpeter method and based on Cornell model, we study the D wave in Bq (=d charmed meson decay, s, c) in the 1-, and the excited state of the strong decays of charmed mesons found in the experiment. In this paper, we first use the BS method to calculate the Bc meson wave D charmonium half light and non light decay, which is _ (C2) (1~1D_2), only 2 (13D2), and only 3 (13D3).Bc meson is the only by two heavy quarks. The smell of the ground state heavy mesons, and only weak decay, the current theory on the study of D wave decay to the very lack of charmonium. In the current experiment and found that only 2 (3823) most likely 13D2 state of charmonium, while the other two D wave _ (C2 (1~1D_2). Only) and 3 (13D3) currently has not been detected; at the same time, the theory of quark model to estimate the 1~1D_2,33D2 and 13D3 states charmonium at DD* near the threshold, the width is very narrow, can be detected in the experiment. In our calculation, calculated by means of BS hadronic transition matrix element, can effectively contain the relativistic correction of high excited state is very important. Our results show that D bifurcation ratio can reach 10-4 magnitude of wave can couple in Bc decay, has reached the current detection threshold to LHC B factory, a large probability is found that these D in the future the Wave charmonium. On the other hand, the experimental group BaBar and LHCb also found that in recent years a number of excited state open taste charm meson, 2- states of D2 which are possible and 3 state D (s) 3* D wave meson, and other D wave D (s) is still not meson detected. Therefore, the theory of the D wave heavy light mesons in the corresponding Bq (q=d, s, c) make a systematic study of the problems in meson decays, for it has very important reference value in theory and experiment, an important research topic of the content is also in this paper. We use the Salpeter wave function in the process of solving the corresponding weak decay hadronic matrix element, and gives some experimental observable physical quantities, such as before and after the asymmetric semileptonic decays of AFB, charged lepton momentum and angular distribution of spectrum, and half light and non light decay widths and branching ratios. Our results show that the D wave D (s) meson in the corresponding B (s) 琛板彉涓�鐨勫垎鏀�姣斿彲浠ュ埌10-3閲忕骇,鑰孊c鍒癉娉�D浠嬪瓙鐨勫崐鐢靛瓙琛板彉鍒嗘敮姣斿湪10-5閲忕骇.鍙﹀��,瀵逛簬2-鎬佺矑瀛，

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