“We will be measuring even the slightest deviations”
The new particle accelerator MESA (Mainz Energy-recovering Superconducting Accelerator) is currently being built at the University of Mainz. Particle physicist Prof. Alfons Khoukaz from the University of Münster is contributing his expertise in the Collaborative Research Centre “Hadrons and Nuclei as Discovery Tools”. In this interview with Christina Hoppenbrock he explains what is special about MESA and what contribution his team is making.
Researchers involved in MESA expect new insights into physics beyond the standard model of particle physics. What does that mean?
The standard model describes the elementary particles we already know about, for example the quarks from which visible material is constructed, and the force carriers through which the three important interactions at the subatomic level are triggered. In addition, it describes the Higgs particle, which gives the elementary particles their mass. In spite of the great success of the standard model, there are clear indications that it is still incomplete. Observations point for example to the existence of dark matter, about which we still know almost nothing today and which is not described by this model. So at MESA precision experiments will be carried out, among other things. We will be able to measure even the slightest deviations from the predictions given by the standard model, which will enable us to reveal the nature of the physics beyond it.
There are other, larger particle accelerators. Why is another one needed?
MESA is a special electron accelerator for low energies which – for the first time worldwide – will be using superconducting, energy-recovering technology for a variety of precision experiments. As a result, it will be able to provide the extremely high beam intensities needed for the experiments – and, at the same time, save a lot of energy as it works. In this operating mode, a so-called luminosity – i.e. particle encounters per area and time – will be attained which is even greater than in the Large Hadron Collider at the CERN research centre.
What do you hope for from MESA?
At the moment, my team is concentrating on the so-called proton radius puzzle which, it is hoped, will be solved using the MAGIX experiment. The radius of the proton is a fundamental value which results from the quark structure. There are, however, controversial measurements for this value. For this reason, the aim is to acquire new, high-precision data to measure the electrical and magnetic proton radius. Over and above this, we will be involved in astrophysical measurements which are important for our understanding of element formation in the stars.
With your team, you have developed a cryogenic “jet target”, i.e. one which works at extremely low temperatures. What is that?
This piece of equipment is the centrepiece of the MAGIX experiment. It generates, in a vacuum, a supersonically rapid molecular or atomic beam with which the high-intensity MESA electron beam interacts. For this purpose, the target gas – reduced to cryogenic temperatures – is pressed through fine nozzles, which our group produces. What’s special about this jet target is the locally high, constantly adjustable density at the point of interaction with the electron beam. As a result, this means that we can make precise examinations of extremely rare reaction processes.
What does this involvement in MESA mean for you and your group?
It will be a very exciting time, helping to set up the new experiments and being able to watch MESA go into operation. What’s special about the MAGIX experiment is not only that it was developed for special measurement work but also that it enables a wide range of questions to be worked on. Our students can contribute new ideas and take part in preparing the experiment as well as in the actual measurements and data evaluation.
When is MESA due to go into operation?
MESA will be going into operation in several stages. In the start phase MESA will be providing a reduced-energy electron beam for initial experiments, probably in late 2025. Around four years later, MESA will be completely ready for use and will have the important energy-recovering mode for high-intensity electron beams.
This article originates from the university newspaper wissen|leben No. 1, 29 January 2025.