研究超出夸克模型的新强子态（奇特强子态）是当前强子物理领域的热门研究方向。X(3872)粒子自发现以来一直吸引了大量的关注，关于其内部结构目前存在诸如强子分子态、四夸克态等理论描述。为理解X(3872)粒子的内部结构，需要对其性质做进一步的精确测量。X(3872)粒子衰变的绝对分支比是该粒子的基本参数，对理解粒子内部结构、分析内部各种组分比例、寻找可能未被发现的衰变模式等均具有重要的指导意义。目前，国际上对X(3872)粒子衰变分支比的测量都是基于相对测量的结果，绝对分支比的测量尚属空白。本项目拟在北京谱仪（BESIII）实验首次展开X(3872)粒子衰变绝对分支比的直接测量。另外，还将研究X(3872)粒子在BESIII实验的辐射跃迁产生机制。该机制首次将两个奇特态强子Y(4260)、X(3872)关联起来，为理解目前粲偶素能区观测到的奇特态粒子提供了新的思路。

The study of new hadron state (exotic hadron state) beyond the quark model is a hot topic in the hadron physics community. Since its discovery, the X(3872) is mostly discussed, and widely interpreted as a good candidate for a hadronic molecule or a tetraquark. In order to reveal its internal structure, more experimental measurements are needed. The absolute decay branching fraction of the X(3872) is a essential parameter of the particle, and provides important information about its internal structure, the contribution of different components in the wave function, and for predicting missing decay channels. At the moment, all experimental measurements about X(3872) decay branching fraction are relative to a reference channel. The absolute decay branching fraction is still not measured. This proposal will perform the first measurement for the absolute decay branching fraction of the X(3872) at the BESIII experiment. In addition, we will study the unique production of X(3872) at BESIII, namely via the radiative transition of the Y(4260) particle. The radiative transition from Y(4260) to X(3872) for the first time brings a connection between two exotic particles, and sheds light on the nature of the exotic particles observed in the charmonium energy region.