The Spectroscopy of Antihydrogen

Understanding and explaining the origin and evolution of our Universe has been at the heart of scientific endeavour for centuries. Recent decades have seen spectacular advances, as particle physics and cosmology have combined to provide the beginnings of a coherent picture. Our Universe seems to have been born in a cataclysmic event called the Big Bang, and has continuously evolved over the 13-14 billion years since then. Though much of the visible Universe can be explained, there are still many very profound mysteries, and none more so than that posed by the existence of antimatter.Simply put, antimatter remains a mystery to Physics. Whilst the symmetry of the laws of nature, and in particular quantum mechanics, demands its existence, the Universe appears to be composed entirely of matter. Addressing this conundrum is one of the great challenges of basic science. As the hot Universe cooled shortly after the Big Bang it appears that all of the antimatter vanished, leaving a tiny excess of matter. At one part in a billion, this doesn't sound much, but the entire material Universe is created from it. The problem is we don't understand how this came to be. There are asymmetries in the behaviour of matter and antimatter, but they are too small by many orders of magnitude to account for the existence of the Universe. One way to address this problem, and the way we have chosen, is to study the antihydrogen atom - the building block of antimatter, and an atom that the Universe never got the chance to make. Recent years have seen great progress in our capabilities with low energy antiparticles (antiprotons and positrons). We can routinely collect many of them in vacuum and store them until we are ready to gently mix them to form antihydrogen under very controlled conditions.Although this capability has opened up great opportunities, there is still much work to be done before the properties of antihydrogen can be compared to those of hydrogen. In this project we will begin along this road by performing a series of experiments on antihydrogen atoms which we have manufactured and trapped in a special device. The apparatus has several parts, but the most important is a trap which can hold neutral species, such as antihydrogen. The trap is formed by magnetic fields from a complicated coil arrangement that forms a magnetic field minimum in the centre of the antihydrogen production region. Antihydrogen, like hydrogen, has a tiny magnetic moment - think of the orbiting positron as a minute current loop - which means that the energy levels shift in an applied magnetic field. Those atoms whose potential energy increases in the field will prefer to sit at the magnetic field minimum, and will be trapped.The depth of the trap is very shallow, just below the equivalent of one degree Kelvin, so we have to make our anti-atoms under very controlled conditions. Once they are trapped we will shine photons on them to interrogate their internal structure. First experiments are likely to be with microwaves, which will help us to compare with the famous 21 cm line of hydrogen. Eventually we will be able to shine laser light onto the antihydrogen.If any differences between the properties of hydrogen and antihydrogen are found, we will have discovered new physics, and perhaps come some way along the road to discovering what happened to antimatter in the early Universe.

Direct academic beneficiaries have been covered elsewhere. Other beneficiaries include the stakeholders in the research and the students and staff who participate in the research. An important UK stakeholder is the EPSRC itself. Concerning publicity for the results of the antimatter research it has sponsored, in the past the interaction between investigators and the EPSRC has, by and large, been weak. Establishing more formal links between the investigators/University marketing groups might prove beneficial. Direct benefits accrue from the output of trained personnel. At postgraduate level, students are given a unique opportunity to interact with physicists from a range of sub-disciplines and to work for extended periods at CERN, the world's flagship physics laboratory. The strict scheduling and attention to detail required for the demanding antiproton shift work gives these students an edge to their repertoire of skills. They are also given the opportunity to develop leadership skills at an early stage of their career, as they are often entrusted with the charge of sub-tasks to be used by the collaboration. PDRA's are given a great opportunity to develop leadership skills. Significant sub-tasks are delegated to them, and they are given the chance to lead individual shifts and eventually to assume a temporary run coordinator position, where they are responsible for delivering the agreed scientific/technical milestones of the collaboration over a period of typically 1-2 weeks. Public interest in antimatter continues to be high. Given that grand societal aims are to raise the public awareness of what scientists do, and why, and to promote science to school children as offering a potentially exciting and fulfilling career, it would appear that our work can be of benefit here. Members of the Swansea and Liverpool teams are active in outreach in the UK. Talks on antimatter are frequently given to local scientific and astronomical societies as well as to organisations such as IoP Branches and University Physics Societies. Charlton has addressed groups of physics school teachers on several occasions and he is also on the Board of the Welsh Stimulating Physics initiative. Van der Werf is a STEM Ambassador connected with the Techniquest Science Discovery Centre, based in Cardiff. We will continue to develop these links. In particular, the Swansea-based Welsh Institute for Mathematical and Computational Sciences is the Welsh spoke in the new National HE STEM Programme, which is coordinated from Birmingham University. The roll-out of this Programme is just beginning such that there are great prospects for enhanced engagement and collaboration.