Jefferson Laboratory Upgrade Project

Approximately 98% of the mass of nucleons, and therefore of the visible universe, emerges from the interactions among their constituents, the quarks and gluons. The Higgs mechanism, which gives mass to the bare quarks, is responsible for only a small fraction of the nucleon mass. The confinement of quarks within mesons and baryons is a direct consequence of their fundamental interactions. The field theory of the strong nuclear force, Quantum Chromodynamics (QCD), is now well established, and yet the phenomena described above cannot be understood from the QCD Lagrangian; they are emergent properties that arise from the unique complexity of these interactions. QCD is as yet intractable at the mass scale of nucleons and nuclei, so a clear picture of the fundamental nature of matter at these energies does not yet exist. However, this situation is set to change, and both theoretical and experimental developments in the coming decade are expected to revolutionise our understanding of nuclear matter within the context of QCD and the Standard Model.

There are several key questions that will be addressed by the work proposed here:

* What is the mechanism for confining quarks and gluons in strongly interacting particles (hadrons)?

* What is the structure of the proton and neutron and how do hadrons get their mass and spin?

* Can we understand the excitation spectra of hadrons from the quark-quark interaction?

* Do exotic hadrons (multiquark states, hybrid mesons and glueballs) exist?

* How do nuclear forces arise from QCD?

* Can nuclei be described in terms of our understanding of the underlying fundamental interactions?

The scientific vision behind the upgrade to the Thomas Jefferson National Accelerator Facility (JLab) in Newport News, Virginia, is to address fundamental issues such as how constituent quarks acquire mass, and why they are confined. It is therefore ideally suited to tackling the pivotal questions laid out above. New insights into the fundamental structure of the nucleon will be obtained from measurements of nucleon form factors, Generalised Parton Distributions (GPDs) and Transverse Momentum-dependent parton Distributions (TMDs). The fundamental nature of QCD confinement will be studied through the investigation of the light hadron spectrum, and the search for the existence of exotic states, in which the confining gluonic field provides an additional degree of freedom to the quarks. These states are a direct prediction of the QCD theory but remain unobserved experimentally.

The Jefferson Lab 12 GeV Upgrade offers an exciting opportunity for the UK Nuclear Physics community to lead and instigate world-leading hadron physics research. The central scientific motivation for undertaking this project is a continuing desire to understand QCD physics: to obtain new information on the structure of nucleons, and to investigate the mechanism of quark confinement. This proposal represents a bid by the Edinburgh and Glasgow nuclear physics groups to build on established leadership roles, and enhance their impact on JLab's future science programme for the coming decades.

The understanding of nuclei and their properties has led to the development of nuclear power plants and an extensive range of applications in the healthcare sector. Experiments designed and constructed by nuclear physicists are driving the development of radiation detectors, electronic systems and computing algorithms for applications ranging from radionuclide imaging, the monitoring of radioactive waste to security applications. The technologies developed for nuclear physics experiments find widespread applications in nuclear physics research, interdisciplinary research activities and industry. The understanding of nuclear physics itself is important for every citizen wishing to make an informed decision on a variety of issues, from personal healthcare treatments to wider political questions. Modern nuclear physics experiments rely on large scale computing facilities and have developed sophisticated data handling and analysis techniques. These computational techniques find applications in a wide range of problems from economics to medical imaging.

We collaborate with academic and industrial partners, using our expertise and knowledge in a variety of fields, from detector design and construction for the nuclear industry to applications of detectors and accelerators in new forms of cancer treatment. The group's expertise in research and the design, simulation and construction of a variety of detector systems provides a very strong position for knowledge exchange activities, from radionuclide imaging to nuclear monitoring and security applications. Through our work in learned societies, such as the IoP and the EPS, we contribute to the promotion of the field and science in general to the general public.

The academics and researchers of the nuclear physics group play an essential role in training early career researchers in a large variety of technological skills, data analysis and physics interpretation. Graduates of the Nuclear Physics group are employed in a large variety of sectors, from academia to finance, from the NHS to the nuclear industry and national security.