Towards a general understanding of near-threshold structures in heavy-hadron spectrum

摘要：

Tremendous progress has been made experimentally in the hadron spectrum containing heavy quarks in the last two decades. It is surprising that many resonant structures are around thresholds of a pair of heavy hadrons. By constructing a nonrelativistic effective field theory with open channels, we discuss the generalities of threshold behavior, and offer an explanation of the abundance of near-threshold peaks in the heavy quarkonium regime. We show that the threshold cusp can show up as a peak only for channels with attractive interaction, and the width of the cusp is inversely proportional to the reduced mass relevant for the threshold. We argue that there should be threshold structures at any threshold of a pair of heavy-quark and heavy-antiquark hadrons, which have attractive interaction at threshold, in the invariant mass distribution of a heavy quarkonium and light hadrons that couple to that open-flavor hadron pair. The structure becomes more pronounced if there is a near-threshold pole. Then, to get an overall feature of the spectrum of hadronic molecules composed of a pair of heavy-antiheavy hadrons, namely, which pairs are possible to form molecular states,we approximate the near-threshold interaction by the resonance saturation with the light-vector exchanges. In total, 229 molecular states are predicted. The observed near-threshold structures with hidden-charm, like the famous X(3872) and Pc​ states, fit into the spectrum we obtain. Lots of the predicted states are to be explored experimentally.

报告人简介：

郭奉坤，中国科学院理论物理研究所研究员。2007年在中科院高能物理研究所获得博士学位，随后在德国于利希研究中心以及波恩大学从事博士后研究工作，并担任德国DFG项目负责人。2015年加入理论物理研究所。主要从事强子谱、有效场论等方面的研究工作。获第7届胡济民教育科学奖，曾担任Chiral Dynamics, PhiPsi, HADRON等国际会议的国际顾问委员会委员。已发表学术论文百余篇，包括Rev. Mod. Phys.和Prog. Part. Nucl. Phys. 特邀综述各1篇，Phys. Rev. Lett. 10 篇，总引用6000余次，h因子43。