分析Belle實驗中 純粹e^+ e^-→D^(*±) D^0 π^∓和e^+ e^-→D^(*+) D^(*-) π^∓過程

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题名:	分析Belle實驗中純粹e^+ e^-→D^(±) D^0 π^∓和e^+ e^-→D^(+) D^(*-) π^∓過程
作者:	陳志瑋;Chen, Chih-Wei
贡献者:	物理學系
关键词:	燦粒子;三體生成;Charm meson;Three body production
日期:	2018-07-04
上传时间:	2018-08-31 13:56:56 (UTC+8)
出版者:	國立中央大學
摘要:	現今的高能物理分析中，時常需要利用到蒙地卡羅法的模擬，並與實驗數據做比較，藉此進一步了解其中的物理現象。現今常用蒙地卡羅方法採用兩種物理模型Pythia與Herwig(在KEK是使用的是Pythia )來預測粒子生成時的狀況。針對這粒子生成時的模型，在2006年K. Odagiri曾提出利用Perturbed QCD[1]的方式，得到可以與 Belle 的實驗數據大是相似但不一致的結果，這使我們想要了解真正粒子生成機制。在我們的分析中，我們測量了純粹三體〖D^(-) D^0 π^+〗_(.cc)與D^(+) D^(-) π^0的反應截面，分別為：σ_(〖D^(-) D^0 π^+〗_(.cc) )=997.27±131.41(fb)、σ_(D^(+) D^(-) π^0 )=603.43±35.69(fb)；藉由比較純粹兩體與三體的反應截面發現，實驗數據比較接近Cluster model (Herwig)的描述，在我們的分析中發現，在質心座標中，π 介子比較傾向於與任意的一個D介子以相同方向前進，另外有許多的D^(±)或〖D^0〗_(.cc)的事件是來自於高質量共振態的衰變，經過我們的估算發現這些二體共振態的反應截面與σ_DD的大小相近，測量Vector⁄Pseudoscalar的比例結果為0.605±0.087，考慮高質量共振態的影響，我們認為使用純粹多體的計算是比較理想的方法。 ;Nowadays, it’s common to simulate the experimental data by Monte Carlo method in analysis of high energy physics events, and in this way we hope to have deeper understanding of its physical meaning. There are two general accepted physics models in Monte Carlo simulation to predict particle generation, namely Pythia and Herwig (Pythia is adopted in our experiment). In 2006, K. Odagiri intended to examine which model can describe data of Belle experiment, but he ended with another Perturbed QCD[1] model which suited data best, and this is the reason why we want to know “Mechanism of particle generation” In our analysis, we measured cross sections of pure three body 〖D^(-) D^0 π^+〗_(.cc) and D^(+) D^(-) π^0 processes to be 997.27±131.41 (fb)-1 and 603.43±35.69 (fb)-1 respectively. By comparing cross sections from pure two body and three body, our data favors Cluster model’s (Herwig) simulation. Our analysis also indicates that pion usually moves forward together with D meson in center mass frame. There are many D^(±) or 〖D^0〗_(.cc) come from from higher resonance decays, we estimate cross section of DD_H (D_H means P-wave D mesons), we find that cross section of σ_(DD_H ) is almost equal to σ_DD. Results of our analysis can lead to measurement of Vector⁄Pseudoscalar ratio to be 0.605±0.087 by comparing 〖D^(-) D^0 π^+〗_(.cc) and D^(+) D^(-) π^0, which consists with exclusive two body DD results and disagrees with inclusive charm meson measurements partially due to its incorrect assumption of none higher mass resonances.
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