Since October 2024, Tyler Kutz has been a tenure-track Professor of Experimental Hadron and Nuclear Physics at the Institute for Nuclear Physics, where he is a PI in the cluster of excellence PRISMA⁺. After a postdoctoral researcher stay at the Massachusetts Institute of Technology (MIT), he moved to Mainz for his professorship, where his expertise in electron scattering is a decisive enrichment to the MESA (Mainz Energy-recovering Superconducting Accelerator) team. “With electron scattering, I investigate the nuclear structure and fundamental interactions,” Tyler explains.
As an active member of international collaborations, Tyler has been active in Mainz since the beginning of his career. “My first doctorate project dealt with the development of detectors for parity-violating scattering of electrons. During this time, I traveled to Mainz several times to carry out beam tests at MAMI, so I am already familiar with Mainz and its experiments. Now I am very much looking forward to working on MESA.”

The future of MESA

MESA is a unique institution that offers a variety of new opportunities for basic physical research and has two main experiments: MAGIX and P2. In the so-called “Energy Recovery Linac” mode, the MAGIX experiment is operated with very high beam currents. The P2 experiment will run in “extracted beam” mode, in which the beam can be recirculated a third time, gaining an additional 50 MeV of energy. The accelerator will be commissioned in a start-up phase at the end of 2025 and gradually ramped up in several stages. MESA will be fully operational around 2029. “I am looking forward to contributing to the measurements of the weak mixing angle and the skin thickness of the lead neutron at P2, as well as the measurements of the proton form factor with MAGIX.”

Tyler’s contributions to P2 will build on his experiences as a doctoral candidate and postdoctoral researcher. Since 2012, Tyler has been involved in the PREX and MOLLER experiments at the Thomas Jefferson National Accelerator Facility (JLab). Like the MREX experiment at P2, PREX used parity-violating electron scattering (PVES) to study the neutron distribution in ²⁰⁸Pb. The so-called neutron skin thickness of heavy, neutron-rich nuclei has important implications for nuclear theory and can be used to determine the properties of nuclear matter and neutron stars. MOLLER, like the Flagship P2, will use PVES to determine the weak mixing angle, a measure of the relative strength of the weak and electromagnetic interaction, with high precision. It can be calculated theoretically very precisely and is therefore an important quantity in the search for physical phenomena that cannot be explained by the Standard Model of Particle Physics (so-called “new physics”). Discrepancies between experimental data and theoretical predictions may indicate the existence of such effects.

The MAGIX experimental hall is located directly next to P2. The MAGIX spectrometer with its innovative gas jet target will investigate the structure of protons and light nuclei. “In fixed-target experiments, the target is usually solid or liquid, so the scattered electrons have to pass through a lot of material, which impairs the measurements. Such a gas target, which has already been extensively tested at the local MAMI accelerator, significantly reduces multiple scattering and the generation of background, as the walls required for many conventional targets are eliminated. These effects are further reduced by the “windowless connection” between the spectrometers and the scattering chamber. This will improve our understanding of nucleon form factors, provide important information for precise electroweak studies and enable the search for dark photons.

In addition to participating in the existing experimental program at MAGIX, Tyler also hopes to make some new contributions. “I am interested in launching a measurement campaign on two-photon exchange (TPE) with MAGIX. Specifically, this involves beam-normal single-spin asymmetries (SSA), in which the electron beam is polarized transversely to its momentum,” Tyler explains. SSAs arise from the interaction between the dipole moment of the electrons and the magnetic field of the target during electron scattering. Since this effect cannot occur when exchanging a single photon, SSAs react directly to the exchange of multiple photons. The role of TPE in electron scattering has attracted a great deal of attention in both theoretical and experimental nuclear physics as researchers try to understand its relationship to hadron structure. “One of my first projects here in Mainz is to figure out how to best use MESA’s unique capabilities to measure SSAs.”

Strong international cooperation

In addition, Tyler is paving the way for close international collaboration between JGU and the Electron-Ion Collider (EIC), a new facility to be built at Brookhaven National Laboratory. “With high-energy electron-ion collisions, we can study the properties of quarks and gluons in hadrons. I have been very actively involved in this project and look forward to continuing to be involved in the future. The EIC is the successor to the Hadron-Electron Ring Accelerator (HERA), a lepton-proton collider that was in operation at DESY in Hamburg until 2007 and whose data are still leading to new discoveries. The EIC will have a lower maximum center-of-mass energy than HERA, but will achieve higher luminosities, enable electron-nucleus collisions and cover a larger phase space for polarized collisions. The EIC is expected to be operational in the mid-2030s and will enable fully polarized collisions with energies up to 18 GeV for electrons and up to 275 GeV for protons. The hadron beam can also consist of complex nuclei, from light elements such as deuterium and helium to heavy elements such as lead. “I am looking forward to extending the measurements to heavy nuclei, where the distribution functions of the nuclear partons are strongly modified compared to lighter nuclei or free nucleons. This extension could provide valuable insights into nuclear dynamics.”

Another focus of Tyler’s research at the EIC is measurements of double-spin asymmetry, which are sensitive to the spin alignment of the quarks in the target. Such measurements have the potential to solve the puzzle of proton spin – a long-standing question in nuclear physics. The EIC is expected to provide crucial clues about the composition of proton spin, especially at low momentum fractions, where the contribution of gluons should be large.

Tyler is pleased to be returning to Mainz as a professor. “In the USA, I had the opportunity to apply for a position at a national laboratory such as JLab, which offers the advantage of working directly at the accelerator, among other things. But I have always preferred the university environment and I enjoy teaching,” says Tyler. “MESA offers the unique opportunity to have access to a state-of-the-art electron accelerator for nuclear physics experiments on a university campus. There are very few other places that can offer this with an infrastructure and research of this caliber.”