BESIII实验在chi_c1衰变中寻找1-+奇特强子态

In quark model, hadrons consist of a pair of quark-antiquark or three quarks (antiquarks). However, the QCD theory of strong interaction allows existence of the so called new types of hadron such as glueball, hybrid, multiquark state etc. Search for and research of new types of hadron is essential for understanding how hadrons form, examining and developing the QCD theory in low energy region. The pi_1(1600), being a 1-+ exotic state, has been considered as a hybrid candidate for a long time. Up to now, pi_1(1600) was only observed in piN scattering and ppbar annihilation. Only one reported evidence of pi_1(1600) in chi_c1 decays, but no solid conclusion was made due to limited statistics. BESIII experiment has collected the world largest psi' decay sample (hence the largest chi_c1 decay sample), providing a perfect place for search for pi_1(1600) and other 1-+ exotic states in chi_c1 decays. In early studies, we have already observed the pi_1(1600) in chi_c1->eta' pi+ pi- with 7sigma significance. With BESIII's data sample, we plan to 1) measure pi_1(1600)'s mass, width, branching ratio, and 2) search for pi_1(1600) in its other decay modes, and 3) search for other 1-+ exotic states.

夸克模型认为强子由一对正反夸克或三个正（反）夸克组成，然而量子色动力学允许强子以胶球、混杂态、多夸克态等“新型强子”组成方式。实验寻找和研究新型强子，对深入了解强子组成、检验和发展低能区量子色动力学具有重要意义。pi_1(1600)发现于上世纪80年代，是最重要的1-+混杂态候选者。迄今pi_1(1600)只在piN散射和ppbar湮灭过程中被观测到，仅有一例报道在chi_c1的强衰变过程中观测到可能存在的迹象，因统计量限制无法给出确定结论。BESIII实验采集了世界上最大的psi'衰变样本，前期研究中我们使用该样本在chi_c1->eta'pi+pi-过程中观测到pi1_(1600)粒子存在，显著性超过7sigma。我们计划使用BESIII的chi_c1衰变数据，测量pi_1(1600)质量、宽度及衰变分支比，寻找pi_1(1600)的其它衰变模式，以及寻找其它的1-+奇特态。

强子组成是高能物理实验领域的重要课题之一，对于帮助理解强相互作用非常重要。BESIII实验的一项主要物理目标即是在轻强子谱中寻找和研究新型强子态。我们关注的是具有1-+奇特量子数的强子态（特别是pi1(1600)），这种强子态的量子数说明它不是通常的夸克模型的强子，因此具有很高的研究价值。我们主要计划通过BESIII采集的世界上最大的psi'和J/psi粒子衰变样本对其进行研究，包括psi'->gam chic1, chic1->eta' pi+ pi-过程的分波分析、psi'->gam chic1, chic1->f1 pi+ pi-过程的研究等策略。目前我们在psi’->gam chic1, chic1->eta' pi+ pi-过程中基本确认pi1(1600)的存在，并测量了其质量和宽度等物理性质；在其他的psi'衰变中尚未确认具有统计意义的pi1(1600)信号。