Cluster of Excellence – Precision Physics, Fundamental Interactions and Structure of Matter (PRISMA+)

The Cluster of Excellence PRISMA+ addresses the basic questions about the nature of the fundamental building blocks of matter and their importance for the physics of the universe. PRISMA+ consists of renowned research groups that work primarily in the areas of astroparticle, high energy and hadron physics, nuclear chemistry as well as precision physics with ultra-cold neutrons and ion traps. Conducting various new key experiments to study the fundamental forces and limits of the Standard Model is one of the main initiatives of the Cluster. PRISMA+ is divided into five research areas and three structural initiatives:

Research Area A "Exploring the intensity frontier at MESA" is devoted to exploiting the unique physics opportunities provided by the MESA accelerator and its experiments MAGIX, P2 and BDX@MESA. The P2 experiment will set a new precision standard for the measurement of the electroweak mixing angle at low energy and enable a new generation of experiments for parity-violating processes that are required for the determination of the neutron skin in heavy nuclei. The MAGIX spectrometer with its novel pseudo-internal gas-jet target will allow for a more accurate extraction of the proton charge radius via electron-proton scattering, as well as searches for messenger particles to the dark sector. The production of dark matter particles and the detection of their decay signatures will be pursued in the beam-dump experiment BDX@MESA. This is complementary to the direct searches for WIMP dark matter that forms the galactic halo.

Testing the Standard Model at low energies is the focus of Research Area B "Precision physics at the low-energy frontier". The main activities include a comprehensive study of the anomalous magnetic moment of the muon, the lifetime of the neutron, the charge radii of the proton and light nuclei, as well as searches for new physics via atomic parity violation. This research relies crucially on sophisticated experimental techniques that have been pioneered by PRISMA+ researchers, including laser spectroscopy of muonic and electronic atoms, magnetic trapping of neutrons, and the technique of initial state radiation at e+e- colliders. Another major focus is the reliable determination of hadronic contributions to the anomalous magnetic moment and charge radii.

Research Area C "Exploring the weakly interacting universe" focuses on the profound open questions related to neutrino masses and the existence of dark matter. The neutrino mass hierarchy and the absolute scale of neutrino masses will be addressed via crucial contributions to the JUNO, PINGU and Project 8 experiments. Searches for WIMPs will employ the world-leading XENONnT and DARWIN experiments. Highly innovative searches for axions and axion-like particles will be carried out at Mainz using the GNOME and CASPEr experiments, and through a leading involvement in the DM Radio experiment located at Stanford University.

Research Area D "Physics at high-energy accelerators" is devoted to indirect searches for new physics at the energy frontier. It brings together researchers from theory and a wide range of experiments to focus on solving major fundamental questions. The primary focus lies on the exploration of the deeper mechanism underlying electroweak symmetry breaking both at the LHC and at a future electron-positron collider. The relevant observables include the couplings of the Higgs boson, the mass of the W boson and a variety of diboson production rates. This program is complemented by searches for rare flavor-changing processes in the NA62 experiment at CERN and at the upcoming Belle II flavor factory. A third research direction is devoted to long-baseline neutrino experiments, whose main target is a measurement of CP violation in the lepton sector.

The activities of Research Area E "Theory and phenomenology of fundamental interactions" are centered on advanced methods in quantum field theory, such as high-order perturbative calculations, applications of effective field theories, and new techniques in lattice gauge theory. Other important areas of research include physics beyond the SM, astroparticle physics, mathematical physics and string theory. PRISMA+ theorists not only work at the forefront of their respective fields but also provide the vigorous theory effort required to accomplish the key research objectives set out in this proposal.

Research in Theoretical Physics at PRISMA+ is further strengthened by the Mainz Institute for Theoretical Physics (MITP). MITP is a community-driven platform for international visiting scholars to discuss the key questions at the frontiers of their field. Founded in 2013, MITP has rapidly evolved into an internationally recognized and highly regarded center for scientific exchange and collaboration.

The Mainz Energy-Recovering Superconducting Accelerator (MESA) will explore the physics opportunities offered by using the recently established Energy-Recovery-Linac (ERL) accelerator technology which enables very high electron-beam luminosities on internal targets at low energies. MESA will be the first accelerator to investigate multiturn energy recovery in a superconducting environment.

The PRISMA Detector Lab promotes the collaboration and facilitates the exchange of experiences and technologies within PRISMA+. It consists of laboratories and workplaces, where scientists with different expertise and students share a common environment and infrastructure.

Researchers in PRISMA+ also make use of the TRIGA reactor and neutron source, which offers unique opportunities for studying the properties of the free neutron with exceptionally high precision, and of the existing MAMI accelerator.