Consolidated Grant

Lead Research Organisation: University of Glasgow
Department Name: School of Physics and Astronomy

Abstract

The research programme of the Glasgow Nuclear Physics Group focuses on the study of the strong interaction. As one of the four fundamental forces in nature, the strong force is responsible for the formation and stability of atomic nuclei. At an even more fundamental level it also is the interaction that forms hadrons from quarks and gluons and is therefore responsible for most of the visible mass in the universe. Quantum Chromodynamics (QCD) is widely accepted as the fundamental theory describing the strong interaction; a recent Nobel Prize (2004, Gross, Politzer, Wilczek) was awarded for developing this theory. QCD has some features that make it very different from the theories of the electromagnetic and weak interactions. Only very high energy particle physics processes can easily be calculated pertubatively, a feature known as asymptotic freedom. At lower energies, effective field theories incorporating some of the fundamental symmetries of QCD, e.g. chiral symmetry, can be applied. In addition, models such as the quark model have been developed, which describes strongly interacting particles as either three-quark or quark-antiquark systems. In our research we use scattering experiments to investigate the structure of nuclei and nucleons as well as the spectrum of hadrons. We carry our experiments out at leading accelerator facilities in Europe and the US: Jefferson Lab in Newport News, USA; MAX-lab in Lund, Sweden; MAMI in Mainz, Germany and DESY in Hamburg, Germany. In these experiments we use (often polarised) beams of electrons, positrons and photons. Our research is organised into three themes: - Nucleon Structure Knowing that nucleons are made up of more fundamental entities (quarks and gluons), we need to establish the distribution of matter within them. Form factors and parton distribution functions are used to describe the structure of nucleons. In recent years the theoretical framework of Generalised Parton Distributions (GPDs) has been developed that ties the description of nucleon structure systematically together. Once measured, GPDs will give us a 3-dimensional picture of the nucleon as well as a way to access the total angular momentum of quarks inside a nucleon. - Hadron Spectroscopy As composite objects, nucleons can be excited to higher mass states. Whilst the quark model describes a great deal of the excitation spectrum, several predictions must be confirmed to clarify which variant of the quark model most accurately describes reality. Hunting for predicted states is a very difficult task, and involves, amongst other techniques, the use of polarised high energy photons similar to the way in which optical polarisation can be employed to see greater detail. The observation of states beyond the quark model is of fundamental importance in answering the question of why quarks and gluons have never been observed in isolation, even though there is compelling evidence that they must exist. This feature, known as 'confinement', is unique to the strong interaction, and is not observed in any of the other fundamental forces of nature. This can be studied by searching for so-called glueballs and exotic hybrid mesons. - Short-range Nuclear Structure We want to understand how the constituents of atomic nuclei, protons and neutrons (collectively known as nucleons), interact with each other to give rise to a wide range of phenomena. In particular we plan to investigate, what happens when nucleons pass very close to each other in collisions within a nucleus, the strength of interactions involving 3 nucleons and how the nuclear medium affects particles that are created within it. We are also studying few-body nuclei, which can be used to test predictions of Chiral effective field theories.

Publications

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Adlarson P (2015) Measurement of p 0 photoproduction on the proton at MAMI C in Physical Review C

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Adlarson P (2018) Measurement of the decay ? ' ? p 0 p 0 ? at MAMI in Physical Review D

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Adler J (2013) The upgraded photon tagging facility at the MAX IV Laboratory in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

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Adler J. -O. (2013) The upgraded photon tagging facility at the MAX IV Laboratory in NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT

 
Description 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. In this consolidated grant period we have made a number of advances that have helped to move this field forwards.

Some of the highlights from this consolidated grant period were:
* Carrying out high-precision form factor measurements in JLab Hall-A
* Completing the analysis of DVCS and SIDIS measurements with CLAS
* Completing the analyses of data collected with the HERMES detector at DESY, which has led to several highly-cited papers in the area of nucleon structure.
* Completing our involvement in the OLYMPUS experiment at DESY to measure the effects of two-photon exchange processes.
* Completing the data-taking phase in the ongoing programme to measure double polarisation observables at JLab
* Working towards a programme at the upgraded Jefferson Lab, including the search for exotic mesons with CLAS12. This culminated in the submission of a new project grant to STFC.
* Carrying out Compton scattering experiments on few-body nuclei to test theoretical effective field theory predictions.
Exploitation Route The bulk of the scientific findings will be of use to the academic nuclear physics community, in the continuing campaign to understand the nature of the strong nuclear force.

The developments in detector design, electronic readout and data analysis have wider benefits for applications involving radiation sensors, as attested by a research contract that has been awarded to the group by Sellafield Ltd to build a muon detector for muon tomography applications. Additionally, work on the development of photon detection systems will have applications in the improvements of medical scanning technologies.
Sectors Education,Energy,Healthcare,Other

 
Description 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.
First Year Of Impact 2010
Sector Education,Energy,Environment,Financial Services, and Management Consultancy,Healthcare
Impact Types Cultural,Societal,Economic

 
Description Public Understanding of Science 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Type Of Presentation Paper Presentation
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact A perspective of the life and work of Ernest Rutherford:
Ernest Rutherford - his genius shaped our modern world
Europhysics News, vol 42/5, 2011, pp18-21
I J Douglas MacGregor

Distributed to all EPS members.
Year(s) Of Engagement Activity 2012