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Fifty years after the discovery of quarks, we are just beginning to understand how QCD forms hadrons, as protons, neutrons and pions. In particular, answering the fundamental question of the generation of hadronic mass is only just beginning and still requires a great deal of effort. Here, the Higgs mechanism, whilst critical in many areas of Standard Model physics, plays only a minor role. The spectroscopic observation of hadrons has played a key role in the development of the quark model and the strong interaction. QCD predicts a zoo of "exotic" hadrons with more complex istructures than the quark-antiquark mesons and three-quark baryons of the original quark model. Nowadays, there are experimentally observed states that are often assigned to the light meson or charmonium sector, indicating an exotic nature. Such exotic particles include glueballs, hybrids, and tetraquarks. These states not only pose a theoretical challenge, but experimentally it is often difficult to distinguish and characterise exotic and non-exotic hadrons. Here, it helps to compare different production mechanisms and decay patterns. This provides additional constraints and allows a coupled channel partial wave analysis. Therefore, gluon-poor two-photon fusion events and gluon-rich hadronic reactions are used to disentangle the highly populated light meson spectrum. Sophisticated dynamical models and analysis tools need to be applied, respecting unitarity and analyticity. The talk will discuss recent experimental results, techniques and analysis methods in order to identify and characterize exotic and non-exotic QCD states.
Hybrid access via ZOOM:
https://lmu-munich.zoom.us/j/98457332925?pwd=TWc3V1JkSHpyOTBPQVlMelhuNnZ1dz09
Meeting ID: 984 5733 2925
Passcode: 979953
Peter Thirolf (LMU) / Norbert Kaiser (TUM)