Birmingham Nuclear Physics Consolidated Grant 2020

Our proposed research has two broad themes that build upon our world leading areas of expertise.

The first of these involves the study of high-energy nuclear collisions at the Large Hadron Collider, the world's highest energy particle accelerator. The aim of the ALICE experiment is to study nuclear matter, as it would have existed about a millionth of a second after the Big Bang when the Universe was so hot and so dense that nuclei did not exist. In its primordial state nuclear matter consists of its fundamental constituents (quarks and gluons) in a plasma state. We recreate this novel state of matter in our experiment and we are developing ways of studying these high-energy nuclear collisions to discover the properties of the quark-gluon plasma. This is technically challenging and the group has developed a sophisticated electronic trigger system that controls the experiment and is entirely responsible for it. The quark-gluon plasma has remarkable properties, such as an abundance of strange quarks and near-perfect fluidity. In this proposal, we are trying to determine whether size matters by finding the smallest drop of plasma that still retains these properties. We are using grazing collisions to explore the internal structure of nuclei at high energy. And we are looking at the debris of quarks and gluons that are sometimes scattered out of the collision, producing a shower of particles in our detector known as a jet, to study the conditions inside the plasma. We are also performing R&D into new detector technologies based on silicon pixel detectors in which the readout electronics is contained within the pixel.

The second strand extends beyond the quarks to the scale of nuclei. Here the challenge is to understand how the nature of the strong interaction plays out on the nuclear, rather than the sub-nucleon scale. Here the strong force is highly complex, which makes theoretical predictions formidable. Our approach is to make extremely precise measurements of light nuclei to reveal aspects of the 'nuclear force' in systems with relatively few protons and neutrons. These properties can then be used to discriminate between theories and help identify the important interactions. One manifestation of the nuclear force is the observation of clustering in which protons and neutrons clump together inside larger nuclei, for example into alpha particles (two protons and two neutrons). Watching how such nuclei fall apart enables their structure to be unveiled. The Birmingham group has made the world's most sensitive measurements of how the Hoyle state in carbon-12 falls apart into three alpha particles. (The Hoyle state is an excited form of carbon-12 which governs how much carbon and other elements are made in stars, so understanding its structure in detail is of great importance.) We propose to extend this research a number of systems that will provide a deeper insight into phenomena such as nuclear molecules (clustered of nuclear matter bound together by sharing neutrons) and nuclei important for nucleosynthesis. Finally, we are developing an experimental programme to exploit gamma-ray beams to probe with great precision the structure of clustered nuclei via their electromagnetic properties. To-date this tool has provided us with some of the best insights into the structure of light nuclei and we plan to extend these studies to exotic cluster states above the cluster-decay energy threshold. This programme will produce measurements to constrain state-of-the-art theory.

There are three areas of impact related to this proposal: knowledge exchange and industrial engagement, public understanding of science and outreach.
The Birmingham Nuclear Physics Group will seek to maximise impact from its two nationally leading facilities: the MC40 cyclotron and the Positron Imaging Centre led by members of the group. Additionally, the new NNUF accelerator-driven neutron source - a national user facility - will begin delivering beams in 2022-23 and has huge impact potential. While predominantly aimed at the nuclear industry, the UK nuclear physics and fusion communities have been very supportive of the project with isotope production, e.g. for radioactive targets and research, along with detector characterisation and damage being just some of the areas of interest. Other research themes include materials characterisation, nuclear data for both fission and fusion, nuclear waste management testing, high-power target development, medical physics innovations, nuclear metrology and s-process nuclear physics studies. To engage both academia and industry early, in the near term, additional time is being made available at the cyclotron, prior to the new facility coming online, to promote greater involvement. These activities will build upon the group's existing role in the Birmingham Centre for Nuclear Education and Research, - focal point for (nuclear) industrial engagement - including the close ties with robotics research (e.g. through shared PhD students) and undergraduate and postgraduate training courses. The group has significant and growing roles developing impact in European networks such as the European Nuclear Education Network (ENEN), the European Learning Initiatives for Nuclear Decommissioning and Environmental Remediation (ELINDER) programme (distant learning developments) and the IAEA in establishing a network on emergency preparedness and response. We will continue to develop flipped learning packages building on already successful materials produced for EDF (both UK and France) and the Royal Society of Chemistry. Imaging in the form of PET and PEPT (Positron Emission Particle Tracking) is being exploited by industries of all kinds for monitoring, in real time, industrial mixing and flow processes and this facility is undergoing an expansion with new appointments and a focus on optimisation of surface treatment of tracer particles to expand the applicability and reliability of PEPT and PET for functional studies. Similarly, some of the electronics developments that we are carrying out for the upgrade of the ALICE experiment may have wider impact. The hardware developments related to MAPS sensors may have applications to medical physics as well as being relevant for a number of future projects in nuclear and particle physics.
A second strand revolves around the public understanding of science. The research outlined in this proposal has the potential to capture the imagination and to inspire a new generation of scientists. One part of the proposed research programme is involved in studying nuclear matter as it would have existed a fraction of a second after the Big Bang. This aspect is relevant to evolution of the early universe. The other strand focuses on the Hoyle state in 12C, responsible for the synthesis of carbon in stars. Understanding the structure of the Hoyle state is a challenge that is relevant not only to nuclear science but also the origins of carbon-based life itself. The group has an excellent track record in bringing its work to the awareness of the general public via its extensive outreach programme, interacting with local schools and regional science centres and hosting events at the University. We hosted a wide range of events in the last grant period and have recently won IOP funding for experience days for home-schooled children designed to inspire (see Pathways to Impact). We will continue to do this in the next grant period with the aspiration to inform and to educate.