New at PRISMA+: Prof. Dr. Jens Erler


Prof. Jens Erler is a new face at PRISMA+ - but also a familiar one. He was appointed to a professorship in “Precision Measurements for Low-Energy Experiments” in January, but he has been collaborating with colleagues on-site for many years, working mainly on the concept and theoretical basis behind the P2 experiment designed for the new MESA electron accelerator.

Jens Erler is a theoretical physicist and initially conducted research into string theory. Ever since his first postdoctoral research position in the 1990s, however, he has dedicated himself to the field of electroweak physics, which combines electromagnetic and weak forces to provide a unified theory within the Standard Model. “That was when the LEP – the Large Electron Positron Collider – at CERN was able to convincingly confirm many hypotheses relating to electroweak theory,” recounts Jens Erler. “This field of physics fascinated me a great deal at the time and continues to do so to this day.”

His first direct contact with his colleagues at the Mainz Institute of Nuclear Physics came in 2011 during the evaluation of a Collaborative Research Center, for which Jens Erler was responsible as an expert for the P2 experiment. Over the last ten years, this has led to close collaboration, also involving Erler spending two sabbaticals in Mainz. “Frank Maas then planned the P2 experiment for MESA – he wanted it to answer aspects similar to those explored by the Qweak Experiment at Jefferson Lab but relating to low energies,” says Jens Erler.

Specifically, P2 is about using extreme precision to determine the weak charge of the proton, i.e. the strength of the weak force acting on the proton. This can then be used to determine the electroweak mixing angle (also called the Weinberg angle), a measure of the relative strengths of the weak and electromagnetic interaction. At the low energies of the P2 experiment, any potential effects that might be associated with the so-called “new physics” could significantly change the mixing angle. Hence a comparison between the results of precision measurements and the predictions generated using the Standard Model could provide insights into aspects of the postulated new physics.

“Together with my two colleagues from the P2 theory team – Hubert Spiesberger and Misha Gorshteyn – we intend to calculate this theoretical prediction as precisely as possible, to allow for a meaningful comparison with the equally very precise measurements. It is the strong force that is mainly responsible for theoretical uncertainties,” explains Jens Erler. “But we are also interested in the theoretical basics of the P2 experiment as a whole: What can we learn, what advantages does it provide over other experiments and what complementary results can we expect?” The latter applies with regard to the parallel measurements being performed using the LHC, for example. When combined with these, the results of the testing of the Standard Model using the example of the Weinberg angle could be made even more precise.

Extensive preparatory work has already been carried out on the theoretical prediction of the Weinberg angle at low energies. Jens Erler has played a decisive role in this; indeed, there are very few other physicists worldwide who have the required expertise. In addition to the specific factors to be investigated in the P2 experiment, Jens Erler also dedicates himself to the analysis of the electroweak force in general.

Erler is an internationally eminent scientist who, before his professorship in Mainz, conducted research at one of the most prestigious universities in Latin America, UNAM (Universidad Nacional Autónoma de México) in Mexico City. He has published numerous articles in high-profile journals. Jens Erler has already conducted numerous workshops at the Mainz Institute for Theoretical Physics (MITP), where experimental and theoretical colleagues from all over the world have come to Mainz to discuss and upgrade the physics program planned for the MESA accelerator. This has led to the initiation and implementation of extensive theory-related undertakings by the international community. “Thanks to the Excellence Initiative by the German federal and state governments and the establishment of PRISMA and its successor, PRISMA+, the University of Mainz has become an influential hub of particle and precision physics and its profile has been boosted enormously – MESA, PRISMA and MITP are terms that are now known all over the world. It is a great honor to now be here and a part of the PRISMA+ team.”

Jens Erler is married and has two children. Because of the restrictions associated with the COVID-19 pandemic, he and his family have used the opportunity to explore Mainz and the Rheinhessen region by bike. In addition, a recently acquired inland navigation license also makes it possible to explore the Rhine and Main rivers by motorboat.