XXQCD · Excited and exotic hadron resonances from Quantum Chromodynamics

Excited and exotic hadron resonances from Quantum Chromodynamics

"The project addresses the problem of understanding the fundamental structure of matter at the sub-nuclear scale. The atomic nucleus is made up of protons and neutrons, which in turn can be described as composites of constituent particles called quarks. Quarks are however never observed experimentally in isolation and this phenomenon, called ""quark confinement"" must arise from any successful theoretical description of the strong nuclear force. The behaviour of quarks is described by a quantum field theory called quantum chromodynamics (QCD). In QCD, quarks interact with force-carrying particles called gluons and these interactions should lead to confinement but a robust mathematical understanding of this emergent behaviour remains elusive. This project investigates new experimental data on the interactions between heavier charm quarks that might provide new insight into details of the dynamics of the quark and gluon fields. The investigation uses a framework for computing properties of QCD from large-scale numerical simulations called lattice QCD. This method allows the theory to be investigated from first principles on high-performance computing systems. These objectives are important for society as they attempt to answer fundamental scientific questions regarding the nature of matter at the smallest scale we can probe in current experiments. This deeper understanding of how matter behaves will drive fresh scientific discovery and basic research. As the project makes use of large-scale parallel computing systems, the work will also drive development of new methods for large-scale numerical computation and techniques for analysing large data-sets that may find uses in other scientific and technical research directions, giving new societal benefits. The new ideas developed by this project will improve calculations in lattice QCD that investigate how particles interact as they collide in experiments and form short-lived excitations. The overall objective is to investigate recently discovered short-lived excitations seen in experiments creating a pairing of a charm quark and anti-quark known as charmonium. These new excitations, labelled the X, Y and Zs do not fit into the simplest models which described how a charm quark and anti-quark should interact. This inability to accommodate these new discoveries in a simplified approach suggests the quark and gluon fields inside these states exhibit more complex, exotic behaviour. This behaviour should however be predicted by a full treatment of the strong interactions using QCD and the project objective is to develop the necessary techniques to perform these calculations using lattice QCD. The action terminated early as the research fellow takes up a new role. During the project, significant progress towards the goals and objectives were made and the research and collaboration developed during the span of the project will continue beyond the lifetime of the action."

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