北京谱仪实验上带电粲介子衰变到三赝标量末态Dalitz分析研究

As it is difficult to measure scalar mesons precisely in experiments, the related physics has been a puzzle for decades. Currently some scalar mesons with mass below 2 GeV have been well established such as f0(500), f0(980), f0(1370), and f0(1500). These resonances could possibly be tetraquark or glueball states. Dalitz plot analyses of D and Ds meson decays to three pseudoscalar mesons are a key to understand the inner structure of these resonances. Based on the BEPCII electron-positron collider, the BESIII experiment has collected ~16 M D meson pairs, and is the world's largest D meson sample at the production threshold. Also BESIII plans to collect the world's largest sample of Ds pair at the production threshold. D and Ds mesons produced at the threshold come with very low background level, which is a great advantage. Utilizing experimental data from BESIII, this project will work on Dalitz plot analyses of charged D(s) meson decays to three charged pions to measure the ππ S-wave. These analyses will be of great importance for studying the nature of low-mass scalar mesons.

由于标量介子在实验上难以得到精确测量，与其相关的物理在近几十年里一直是一个难题。目前在小于2GeV的质量区间，已充分确立的标量介子包括f0(500), f0(980), f0(1370), 和f0(1500)。这些共振态有可能是四夸克态，或者是胶球态。对D介子和Ds介子到三赝标量介子末态的Dalitz分析是了解这些共振态的结构的关键。基于北京正负电子对撞机BEPCII之上的北京谱仪BESIII 实验已经在psi(3770)共振峰上采集了大约1600万D介子对，为世界上最大的阈值产生D介子对样本。BESIII还计划在不久的将来采集到世界上最大的阈值产生Ds介子衰变样本。阈值产生的D和Ds介子衰变事例具有低本底的优点。该项目利用BESIII上的实验数据，将着力于D+或Ds到三个带电π介子衰变道的Dalitz分析以对ππ的S波进行测量。这些分析将对低质量标量介子性质的研究具有重要意义。

由于标量介子在实验上难以得到精确测量，与其相关的物理在近几十年里一直是一个难题。目前在小于2GeV的质量区间,已充分确立的标量介子包括f0(500), f0(980), f0(1370), 和f0(1500)。这些共振态是四夸克态和胶球态的候选者。对粲介子到三赝标量介子末态的Dalitz分析有助了解这些共振态的结构。基于北京正负电子对撞机BEPCII之上的北京谱仪BESIII 实验于2016年在质心能量为4.18 GeV上获取了积分亮度为3.19 fb-1的数据。利用这批实验数据，我们重建了Ds+ 介子到三个带电pi介子末态的衰变过程。通过对事例选择进行优化，我们最终收集到了大约1万4千个Ds+ -> pi+ pi- pi+ 数据事例，信号纯度为80%。利用GPU加速的Dalitz图分析工具，并采用了模型无关的分波分析方法，我们对Ds+ -> pi+ pi- pi+过程中的pipi S波的振幅和相位进行了详细测量。同时，我们还测量了Ds+ -> pi+ pi- pi+过程中包含矢量和张量介子的中间态的贡献大小。