Astro-, Astroparticle & Neutrino Physics

Johannes Gutenberg University Mainz > Faculty 08 > Physics > Physics Research > Research Areas > Astro-, Astroparticle & Neutrino Physics

Neutrinos are the strangers of the Standard Model. Interacting only weakly with the other particles, a number of key properties of neutrinos are still unknown—including their tiny masses and how these are generated. While Project 8 aims to measure the absolute value of their masses directly, the JUNO and IceCube experiments aim to determine their ordering. One possible mechanism explaining the smallness of the neutrino masses predicts that neutrinos would be their own antiparticles. This would give rise to the phenomenon of neutrinoless double beta decay researched by the NuDoubt⁺⁺ collaboration. More generally, neutrinos and anti-neutrinos could behave differently. This is commonly described by a CP-violating phase which can be observed when comparing neutrino- and anti-neutrino beams at DUNE. Technological development for future experiments and cross-section measurements for accelerator neutrinos are the focus of the ANNIE experiment at Fermilab.

Neutrinos also provide a unique avenue for theoretical research. We explore the origin of their masses, non-standard neutrino interactions, and their possible role in the generation of the matter-antimatter asymmetry (groups of Prof. Harz and Prof. Kopp). Despite many open questions about their properties and origins, neutrinos can serve as cosmic messengers, carrying information from a wide range of astrophysical objects—including the Earth, the Sun, and distant cosmic sources.

ANNIE is a gadolinium-doped water Cherenkov detector performing measurements in the Booster Neutrino Beam (BNB) at Fermilab in Batavia, Illinois, in the United States. The primary goal is the determination of the neutron multiplicity generated by muon neutrino interactions in water as a function of the momentum transfer. The results will impact the reconstruction of neutrino interactions in long-baseline oscillation experiments, but also the search for proton decay and the diffuse supernova neutrino background in future large-scale detectors.

The Mainz group is contributing to the near detectors of the DUNE complex, which are essential for understanding the properties of the neutrino beam and how neutrinos interact with argon. The process of how a neutrino or anti-neutrino interacts with matter can be described as the neutrino exchanging a W- or Z-boson for a neutron or proton within the argon nucleus. To understand this process, it is not only important to understand the energy/momentum distribution of the argon nucleons, but also how the particle produced inside the nucleus interacts when traversing the nuclear medium of the argon nucleus.

The IceCube detector is a cubic-kilometer neutrino telescope deployed in the glacial ice at the geographic South Pole. Its enormous size allows it to study the very rare interactions of astrophysical neutrinos—unique probes from the depths of the universe that can help identify the elusive sources of cosmic rays. At the same time, the properties of neutrinos themselves can be studied from the abundance of observed atmospheric neutrinos and their oscillations on their way through the Earth.

The Jiangmen Underground Neutrino Observatory (JUNO) is a cutting-edge neutrino experiment in China designed to determine the neutrino mass hierarchy with unprecedented precision. Its primary goal is to resolve the ordering of neutrino masses, a fundamental question in particle physics. JUNO is unique due to its massive 20,000-ton liquid scintillator detector, which delivers exceptional energy resolution and sensitivity. Beyond reactor neutrinos, JUNO will also study solar, atmospheric, and supernova burst neutrinos, geoneutrinos, and the diffuse supernova neutrino background (DSNB), offering a broad science program. Thanks to its scale and versatility, JUNO is set to become a key player in advancing our understanding of both neutrino properties and astrophysical processes.

The pre-dominance of ordinary matter over anti-matter in the observable universe is one of the greatest unsolved mysteries of cosmology. Without this asymmetry the universe would be a void. A possible explanation is the process of neutrinoless double beta decay, which proves that matter and anti-matter are identical in certain situations. The NuDoubt⁺⁺ experiment aims to measure two-neutrino and neutrinoless positive double weak decays (2β⁺/ECβ⁺). This is based on a new detector concept combining hybrid and opaque scintillators paired with a novel light read-out technique. The technology is particularly suitable for detecting positron (β⁺) signatures. In its first phase, NuDoubt⁺⁺ is going to operate under high-pressure loading of enriched Kr-78 gas. It expects to discover two-neutrino positive double weak decay modes of Kr-78 within 1 tonne-week exposure, and is able to probe neutrinoless positive double weak decay modes at several orders of magnitude higher than current experimental limits.

For a long time, neutrinos were though to be massless. However, their oscillation provides clear evidence that they are not! The most sensitive method for determining these tiny masses in the lab is the observation of the endpoint of the β-decay spectrum of tritium. The novel CRES method, used to determine the β-energy through faint radio emission, will improve the energy resolution through a more precise measurement of the electrons motion, but also by allowing for the use of tritium atoms rather than molecules. The generation of these atoms poses a major technological challenge as the atoms need to be heated to beyond 2300K to dissociate them but can only be at milli-Kelvin temperatures in the trap. Another challenge is posed by the magnetic fields, as they need a precisely controlled homogeneous region in which the electron energy is measured, and steep walls to trap both electrons and atoms.

T2K is a second generation neutrino oscillation experiment. It uses an off-axis neutrino beam that is produced at J-PARC accelerator complex in Tokai at the east cost of Japan. The accelerator complex will eventually produce the world most intense long baseline neutrino beam by dumping protons at a beam power of around 500 kW onto a carbon target. The resulting neutrinos are first measured by a near detector complex before they continue 295 km to the Super-Kamiokande detector.

The early universe, from the Big Bang to the formation of galaxies and stars, holds the key to several unresolved fundamental questions in physics. These include the dynamics of inflation, the origin of the matter-antimatter asymmetry, and the nature and production of dark matter. Insights into this epoch are gained from observations of the cosmic microwave background, large-scale structures, and, increasingly, from gravitational wave searches.

Our research addresses these profound questions through a variety of approaches. We study mechanisms such as baryogenesis and leptogenesis to explain the origin of the matter-antimatter asymmetry. We investigate phase transitions and the dynamics of the dark sector, which give rise to gravitational waves and other observational probes of the early universe. We also examine inflationary dynamics followed by the (p)reheating of the universe, explore candidates for dark matter, and advance the theoretical foundations of early universe cosmology using quantum field theory in curved spacetime and non-equilibrium quantum field theory. In doing so, we forge strong links between high-energy physics and cosmological observations. On the experimental side, the GravNET experiment will search for gravitational waves at GigaHertz frequencies, with the ultimate goal of probing the early Universe shortly after the end of Inflation and reheating. Complementary probes of the physics of the early universe are pursued in high energy particle physics, including in particular the study of Higgs physics in the context of the electroweak phase transition and quark and lepton flavour physics as a key ingredient of baryogenesis.

The GravNet project (“A Global Network for the Search for High Frequency Gravitational Waves”) bridges particle physics and gravitational wave physics, aiming to establish a global network of detectors dedicated to searching for high-frequency gravitational waves. This detector network could help address one of the major unresolved questions in modern physics: the nature of dark matter.

Astrophysical observations provide overwhelming evidence for the existence of an additional non-luminous matter component in our universe, commonly known as dark matter. Little is known, however, about its properties. In fact, its mass is virtually unconstrained, ranging from ultralight scalar fields with masses much lighter than the neutrinos up to primordial black holes with many times the mass of the sun. Determining the nature of dark matter is therefore one of the key open questions in astro-particle physics.

In Mainz, the CASPEr and GNOME experiments search for ultralight dark matter using highly sensitive spin precession devices and optical magnetometers (group of Dmitry Budker). The XENON experiment searches for collisions of GeV- to TeV-scale dark matter particles with Xenon atoms in a highly shielded underground experiment. The COSI Compton telescope, a satellite to be launched in 2027, will search for gamma-ray emissions from MeV-scale dark matter. Theory groups in Mainz are developing and analyzing new models of dark matter, advancing methods for the theoretical prediction of dark matter abundance and its interactions, and devising novel strategies to search for dark matter. This effort is complemented by collider searches for dark matter particles or their mediators at the MESA accelerator in Mainz as well as within the ATLAS collaboration, see here.

COSI is a space-based gamma-ray observatory designed to uncover the secrets of stellar explosions by detecting radioactive isotopes forged in supernovae. By mapping gamma-ray emissions from isotopes like aluminum-26 and iron-60, COSI will trace the chemical evolution of the Milky Way and reveal where heavy elements are created. It will also search for gamma rays from titanium-44, a key signature of young supernova remnants, offering insight into how massive stars end their lives. COSI will investigate the 511 keV line emitted when positrons annihilate with electrons, helping to identify the sources of antimatter in our galaxy. With its sensitive Compton telescope, COSI will explore the MeV gamma-ray sky—a largely uncharted region—opening a new window onto phenomena like black holes, neutron stars, and gamma-ray bursts.

XENON is a deep-underground experiment designed to detect dark matter particles by capturing their rare interactions with liquid xenon atoms. Buried beneath Italy’s Gran Sasso mountain, XENON uses a dual-phase time projection chamber to search for weakly interacting massive particles (WIMPs), a leading dark matter candidate. The detector looks for tiny flashes of light and electrons produced when a WIMP collides with a xenon nucleus—signals that could reveal the presence of dark matter. The Oberlack group in Mainz contributes to XENON by developing advanced data analysis techniques and precision calibration tools that help distinguish potential dark matter signals from background noise. These efforts will play a crucial role in the upcoming XLCD program, which aims to probe both dark matter and neutrino physics with even greater sensitivity.

How do stars create elements, and what happens to matter under the most extreme conditions in the universe? How are elements forged in our Milky Way? What happens in a supernova explosion? Our research explores these questions by carrying out experiments in the sky and in the laboratory. Our studies on stellar nucleosynthesis and the structure of neutron stars combinines cutting-edge experiments with theoretical modeling. At the high-intensity accelerator MESA, we investigate nuclear reactions essential for understanding how elements form in stars. At the same time, we are exploring the properties of neutron-rich matter to better understand the behavior of matter under extreme densities and the physics shaping neutron stars. The Compton Spectrometer and Imager (COSI) is a satellite mission designed to study stellar physics, specifically focusing on gamma-ray emissions from radioactive isotopes produced in supernovae and the origin of positrons in our galaxy.

The Belle II detector at the SuperKEKB accelerator in Tsukuba (Japan) is an experiment built to search for new physics beyond the Standard Model by measuring rare decays of elementary particles, such as bottom and charm quarks or tau leptons. Belle II will address the problem of finding evidence for the existence of new unknown particles that can provide a possible explanation for the predominance of matter compared to antimatter and answer other open fundamental questions about our understanding of the universe.

The MAGIX experiment (MAinz Gas-Internal Target Experiment), currently under construction, will consist of two magnetic spectrometers with a relative momentum resolution of order 10⁻⁴, provided a spatial resolution in the focal plane of the spectrometers of 100 µm is achieved. MAGIX will operate in beam-dump mode with solid targets and in ERL mode with a windowless internal gas-jet target.

The P2 experiment is a magnetic spectrometer with the main goal to measure the electroweak mixing angle at very low momentum transfer, which becomes accessible by measuring a parity-violating left-right asymmetry in elastic electron-proton scattering.