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Abstract:
The confinement of the strong interaction is not fully understood from first principle QCD calculations. As low energy bound state of the strong interaction, properties of hadrons provide the opportunity to investigate this non-perturbative aspect of QCD. Besides conventional mesons and baryons that are made up of two and three constituents, hadrons with more than three quarks are also allowed, called exotic states. Models motivated by QCD are available to explain their internal structure and interactions, which serves to describe the QCD non-perturbative behavior. In the last years, tens of new hadron states are observed in e+e- and hadron colliders consistent with signatures of exotic hadrons, in particularly those with heavy quarks. However, the limited knowledge doesn't allows us to draw firm conclusions on (1) whether all these structures are genuine hadrons or just dynamically generated (2) how the internal quarks are bound together (3) whether they are connected by some symmetries or dynamics. The LHCb experiment, located on the large hadron collider at CERN, is dedicated for research using heavy flavor hadrons; therefore it is ideal to study exotic hadrons containing beauty and charm quarks. Using run 1 data, LHCb observed a few new exotic states in beauty hadron decays, for example pentaquark states Pc+ and tetraquark states decaying into J/psi phi. With full run 2 data, the highly increased statistics makes it possible to detect many more states. The recent LHCb results on studies of exotic hadrons will be discussed in the talk.
摘要: 强相互作用色禁闭性质目前还没有QCD理论上完全理解。强相互作用使得夸克束缚在强子内部，强子的性质为研究QCD非微扰性质提供了机遇。夸克可以两个或者三个组合在一起形成介子和重子，除此之外，夸克也可以以更多数目结合构成多夸克强子，称为奇特强子态。对于多夸克强子态内部夸克的结合机制和相互作用形式，理论上存在不同的模型来解释。近年来在正负电子和强子对撞机上探测到了多个新型强子结构，特别是含有重夸克的结构可能是多夸克强子态信号。然而目前实验信息仍然有限，无法确认这些结构是否都是真实的强子态还是可能存在纯运动学效应，也不清楚这些结构内部夸克的结合方式以及他们是否会像常规强子态一样遵循味对称性或者由动力学相互联系。位于欧洲研究中心得LHCb实验为研究重味强子而建造，是研究重味多夸克强子结构的理想实验平台。使用一期实验数据，LHCb发现了多个新的奇特强子结构，比如五夸克态Pc+，J/psi phi四夸克态等，结合LHCb二期数据为发现更多奇特结构提供了可能性，这个报告将介绍LHCb实验奇特强子态研究的最新进展
Biography:
Yanxi ZHANG, assistant professor at the Peking University. He received his bachelor and PhD degrees from Tsinghua University in 2007 and 2013 respectively. Then he worked as a postdoc researcher in Tsinghua University (China), CNRS/LAL (France) and CERN (Switzerland) before he moved back to the Peking University in 2020. He has been working with the LHCb experiment for more than 10 years, researching in the field of heavy quarkonium production, heavy hadron spectroscopy, heavy ion collisions and flavor physics. He was involved in studies that allow to observe pentaquark sates, doubly charmed baryons Xicc++ and fully heavy tetraquark state X(900) at LHCb. He served as one of the conveners of LHCb "B-hadron and Quarkonia" (2018.01-2019.03) and "Ions and Fixed-Target" (2019.01-2021.03) physics working group and was a member of the LHCb "operation planning group". In 2020 he received support from Chinese young talent program.
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