摘要
48.1. General Considerations Perturbative methods can be applied to systems of quarks and gluons only for large momentum transfers （see review on ＇Quantum chromodynamics＇） and, under certain conditions, to some properties of systems that contain heavy quarks （see review on ＇Heavy-Quark and Soft-Collinear Effective Theory＇）. In general, however, dealing with QCD in the low momentum transfer region is a very complicated non-perturbative problem where quarks and gluons are confined within color neutral hadrons. Physical states show up as poles of the S-matrix either on the physical sheet （bound states） or on the unphysical sheets （resonances） and manifest themselves as structures in experimental observables. Resonances can show up either in so-called formation experiments typically of the kind
48.1. General Considerations Perturbative methods can be applied to systems of quarks and gluons only for large momentum transfers （see review on ＇Quantum chromodynamics＇） and, under certain conditions, to some properties of systems that contain heavy quarks （see review on ＇Heavy-Quark and Soft-Collinear Effective Theory＇）. In general, however, dealing with QCD in the low momentum transfer region is a very complicated non-perturbative problem where quarks and gluons are confined within color neutral hadrons. Physical states show up as poles of the S-matrix either on the physical sheet （bound states） or on the unphysical sheets （resonances） and manifest themselves as structures in experimental observables. Resonances can show up either in so-called formation experiments typically of the kind
