Search for strange four-quark states in the charmonium sector with BESIII

寻找奇异强子是强子谱学中的一个非常热门的问题。奇特强子的状态不符合传统的分配，即重子的三夸克态或介子的夸克-反夸克态。我们建议利用BESIII实验的新数据和现有数据来寻找已建立的奇异四夸克Z_c态中缺失的奇怪伙伴Z_cs。在最近的一次综述中，对这些Z_cs态的研究被认为是未来几年实验强子谱中最重要的课题之一。用QCD求和规则从理论上预测了J^P=1^+的四个最轻Z_cs衰变通道的质量和衰变宽度。其中两个衰变包括开放的魅力介子，而另外两个通道包括隐藏的魅力介子。通过对这四种衰变模式的识别，我们打算探索电子-正电子湮没中Z_cs和一个带电K介子的联合产生。拟议的复杂分析计划由两名博士生进行。虽然第一个将分析包括两个D介子的末态，第二个将专注于具有Charmonia的末态。因此，这些分析将是相辅相成的，需要在最后的解释中密切合作。通过BESIII实验，到目前为止，我们已经在4.0GeV到4.6GeV的质心能量范围内收集了大约17.1/fB的e+电子碰撞数据，专门用于碳原子区奇异态的光谱研究。北京正负电子对撞机II(北京正负电子对撞机II)升级完成后，将在2019年10月至2020年6月期间收集与本文提出的研究最相关的质心区4.6GeV至4.7GeV的新数据。假设假设Z_cs对e+e-→J/ψK+K通道的贡献与e+e-→J/ψπ+π-中Z_c(3900)的相对强度相同，通过Z_cs衰变为J/ψ和带电Kaon，估计了Z_cs的观测结果。这将标志着对Z_cs的首次观测，这一发现与Z_c(3900)的原始发现一样具有开创性，后者被APS物理选为2013年杰出发现之一，仍然是被BESIII引用最多的出版物。此外，其他三个通道同样重要，因为它们不仅提供了关于Z_cs的重大发现潜力，而且还允许搜索在初始e+e湮灭中形成的新的矢量共振。

The search for exotic hadrons, states that do not fit the conventional assignment as either three quark states for baryons or quark-antiquark states for mesons, is a highly topical issue in hadron spectroscopy. We propose to search for the Z_cs, the missing strange partner of the established exotic four-quark Z_c states, using new and existing data of the BESIII experiment. In a recent review, the search for these Z_cs states was named as one of the most important topics in experimental hadron spectroscopy in the coming years. Both mass and decay widths for four decay channels of the lightest Z_cs with J^P=1^+ have been predicted by theory using QCD sum rules. Two of these decays include open charm mesons while the other two channels include hidden charm mesons. We intend to search for the production of the Z_cs in combination with one charged kaon in electron-positron annihilations via the identification of these four decay modes. The proposed complex analyses are planned to be performed by two PhD students. While the first one will analyze final states including two D-mesons, the second one will focus on final states with charmonia. Therefore, the analyses will be complementary to each other and will require a close cooperation in the final interpretation. With the BESIII experiment, we already collected about 17 1/fb of e+e- collision data in the center-of-mass energy range of 4.0 GeV to 4.6 GeV thus far, dedicated to the spectroscopy of exotic states in the charmonium sector. After an upgrade of the Beijing Electron Positron Collider II (BEPCII), that has already been finished, new data in the center-of-mass region 4.6 GeV to 4.7 GeV most relevant for the studies proposed here will be gathered in the upcoming measurement period between October 2019 and June 2020.Assuming that the relative strength of a hypothetical Z_cs contribution to the e+e- → J/ψ K+K- channel is of the same magnitude as for the Z_c(3900) in e+e- → J/ψ π+π-, an observation of the Z_cs via its decay into a J/ψ and a charged kaon is estimated. This would mark the first ever observation of the Z_cs and a discovery that is equally groundbreaking as the original discovery of the Z_c(3900), which was selected as one of the standout discoveries of 2013 by APS Physics and is still the most cited BESIII publication. Moreover, the other three channels are equally important, as they do not only pose significant discovery potential concerning the Z_cs, but also allow to search for new vector resonances formed in the initial e+e- annihilation.