粲偶素与类粲偶素的实验研究

Many charmonium and charmoniumlike states were discovered at the B-factories, while some of them are good charmonium candidates as predicted in different models, most of these states have exotic properties. This may indicate that exotic states, such as multi-quark state, molecule, hybrid, or glueball, have been observed. In the vector sector, four exotic charmoniumlike structures were reported in the analyses of pi+pi-J/psi and pi+pi-psi' final states via Initial State Radiation,in addition to the three known excited psi states. It is unlikely all these seven states are charmonia, as the potential models predicted only five vector states in this mass region. However, it is very hard to conclude which one is exotic based on the limited experimental information available, and the fact that some of these structures may be produced by some dynamics which are hard to calculate theoretically such as final state rescattering. There are also many charged-parity even states observed such as the X(3872), XYZ(3940), Y(4140) and so on, whose nature are also unknown due to the limited experimental information.BESIII experiment at the BEPCII e+e- collider is a unique experiment designed for charmonium physics study, with the unprecedented luminosity so far reached, it makes the high precision study of the vector charmonium and charmoniumlike states possible. We plan to take data at an energy range from 3.8 GeV to 5.0 GeV with fine step, to measure the e+e- annihilation cross sections into open-charm final states and charmonium contained final states in high precision. By fitting these cross sections simultaneously, the resonance parameters of these states can be obtained, together with the coupling of these states to the final states measured. The charged-parity even states can be searched for via the radiative transition of these excited states, and the excited P-wave spin-triplet charmonium states as well as the S-wave spin-singlet states can also be searched for in the same or similar transitions. The isospin-one charmoniumlike state Zc, which is expected to exist in e+e- to pi+pi-J/psi and pi+pi-hc, can also be studied with data collected at the peak of the Y(4260) and Y(4360). With all these information, a deeper investigation of the natures of these charmoniumlike states and thus a better understanding of the QCD can be achieved.

B工厂运行以来，发现了大量新的粲偶素和类粲偶素（也称XYZ）粒子，它们中很可能存在分子态、多夸克态、混杂态等非常规介子，但目前的数据尚不足以得出确定的结论。北京正负电子对撞机BEPCII上的BESIII实验是目前在粲偶素和类粲偶素能区运行的亮度最高、最稳定的正负电子对撞实验。我们计划在3.8至5.0 GeV之间采集数据，精确测量正负电子对撞产生的含粲介子末态和含粲偶素末态的截面，确定ψ激发态和Y(4008)、Y(4260)、Y(4360)、Y(4660)等矢量态的共振参数及产生与衰变性质；利用矢量粒子辐射跃迁寻找X(3872)、XYZ(3940)等类粲偶素粒子和P波粲偶素激发态；通过粲偶素强子跃迁寻找同位旋为1的类粲偶素态。这些结果将加强对强子结构的深入认识，促进量子色动力学理论的完善和发展；同时我们将着眼于可能出现的新物理现象，发现新的物理规律。

我们利用北京谱仪III（BESIII）探测器在4.0-4.6 GeV采集的约5/fb数据研究粲偶素和类粲偶素的性质。利用正负电子质心系能量4.26 GeV处采集的数据，我们首次发现了奇特态候选者—带电类粲偶素Zc(3900)。在随后的研究中，我们又在pi+pi-hc中间态中发现了Zc(4020)，它极有可能是Zc(3900)的质量较高的伴随态。我们首次观测到X(3872)在Y(4260)辐射跃迁中的产生，这是一种新的X(3872)的产生模式也是一种Y(4260)的新的衰变模式。在e+e--->pi+pi-gamma chi_c1中发现了X(3823)，粲偶素D波三重态之一。首次观测到omega chi_c0过程的产生，并对e+e--->pi+pi-J/psi、pi+pi-hc，etahc、eta'J/psi等过程进行了研究，发现了pi+pi-J/psi、pi+pi-hc中的新的矢量类粲偶素粒子Y(4220)等，对XYZ(3940)、Y(4140)等类粲偶素粒子进行了寻找，对部分粲介子对的截面和D*衰变分支比进行了测量。这些结果为更好地理解量子色动力学和强相互作用提供了关键数据，在深入理解夸克禁闭机制的道路上前进了一步，对于精确检验标准模型理论具有重要的意义。

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