Frequency metrology for precision measurements on matter-antimatter symmetry

The virtual absence of antimatter and preponderance of matter in the Universe today remains one of the biggest conundrums facing physics. Already in 1967, the famous Sakharov conditions described how this asymmetric Universe could come about by requiring symmetry violations (i.e. differences) between matter and antimatter. Until now, no sufficient symmetry violations have been found to resolve this question, thus the puzzle remains. This project aims to seek answers to this question by directly testing the supposition that the structure of atoms made of antimatter is indistinguishable from the structure in their matter counterparts.

This grant proposes the installation of a caesium fountain atomic clock which will allow spectroscopic measurements of antihydrogen with an uncertainty commensurate with how accurately we can measure time itself. This project provides state-of-the-art equipment for our long-term programme where we use this ultimate tool of precision measurements to address the antimatter conundrum. Our approach is to trap antihydrogen atoms, (atoms that we make by combining antiprotons and positrons) in order to study their internal structure using spectroscopic techniques from atomic physics. We draw from work that have given us the most precise gauges in the scientific toolbox to date and the basis for the global positioning system (GPS); atomic clocks. Specifically, we investigate the ground to first excited state transition in antihydrogen (antimatter) held in a magnetic trap to test the hypothesis that the frequency of this transition is exactly the same as that of hydrogen (matter). This transition has been investigated with a staggering 15 decimal places of precision in hydrogen. We have recently achieved a precision of 12 decimal places in antihydrogen. Improving our antimatter-work to match the result in matter experiments requires us to determine the antihydrogen 1S-2S transition frequency with the accuracy of the corresponding measurement in hydrogen. The new equipment is a state-of-the-art atomic clock identical to the type that makes the definition of the SI-second practical. Since the atomic clock directly measures the hyperfine interval in caesium as defined in the SI-system of units, it will give us the best possible absolute frequency reference and allow us to reach the precision achieved in matter with antimatter.

The antimatter research that this project enables , tests the very foundations of physics that explains the world around us and forms the basis technology of increasing complexity. Despite all this success, we still do not understand why there appears to be no bulk antimatter in the Universe. In this project we look for tiny deviations from expectations based on our current understanding. Experience shows that precise observation of Nature leads to breakthroughs in our understanding. Here, antihydrogen is a compelling subject due to the very specific predictions of its properties, and the already available precise results in its matter counterpart. The risk of finding no new clues on this path is far outweighed by the risk of not looking for them when we now very clearly can. An observed difference between antihydrogen and hydrogen that can be attributed to symmetry breaking would have profound, today even unimaginable, consequences on the foundations of physics. Even if no clues are found now, there is immense intrinsic value in the most precise direct measurement of a property in antihydrogen.

The impact of our work is mainly on the communities that are beneficiaries and, other than the direct academic impact (see elsewhere), these include the stakeholders, the students and staff participating in the project, those who benefit from the output of trained personnel and the general public. This summary as well as the pathways document highlights the overall impact of the antihydrogen activity that will be supported by the requested equipment.

The institutional and organisational stakeholders are Swansea University, as well as the Universities of Liverpool and Manchester (the other ALPHA members in the UK), the other roughly 14 overseas institutions in ALPHA, CERN, and the EPSRC itself. With respect to the latter, we are honoured to have been selected several times for inclusion in its celebratory documents, most recently the Pioneer 14 publication to mark the EPSRC's 20th anniversary. For many years now we have worked closely with the marketing offices of the respective parties in the coordination of the release of publicity materials concerning our research advances. As a result, we have amassed many hundreds of features in the popular press, in specialist magazines and on television, radio and social media. We believe that this not only raises the profile of our work and promotes science to a wide audience, but is also mission-fulfilling for the participating institutions. This is certainly an activity that will be continued.

Direct benefits include many highly trained personnel. Our postgraduate students are afforded a unique experience: they interact with, and work directly alongside in many instances, top physicists from the range of sub-fields embodied within ALPHA. They are entrusted with significant sub-tasks, for which they are directly accountable to the entire collaboration, and emerge with a full repertoire of marketable skills, including a proficiency in the French language. Many of our students continue on to postdoctoral positions around the globe. Postdoctoral researchers on ALPHA are afforded similar, though higher level, opportunities within the programme and many assume important physics and technical coordination roles within the collaboration. We are proud of our record of researchers moving into successful academic careers, including one of the investigators on this proposal.

Public interest in fundamental science, including antimatter, remains high and we think that our feature in the 2016 Royal Society Summer Science Exhibition contributed to this trend. As noted in the "Pathways to Impact" we have begun a Swansea-based initiative aimed at increasing the number of physics teachers in Welsh schools and colleges that participate in the CERN visitors and teachers programmes. This is already having an effect, with more teachers now beginning to organise student trips to CERN.

Most members of the UK teams in ALPHA are active in outreach, at many levels, from local science societies to national festivals. CERN-based colleagues, including our postgraduate students, are frequent hosts of tours of the AD in which ALPHA, and the original apparatus used in the first creation of cold antihydrogen, feature prominently.