Exotic atoms are simple Coulomb-bound systems in which an exotic particle, such as an antiproton, muon, or pion, replaces either the nucleus or an electron within a typical atom. These unique atomic configurations serve as highly sensitive tools for probing the Standard Model (SM) at low energies, and offer precise measurements of fundamental parameters, including particle masses and magnetic moments. Experiments involving exotic atoms contribute valuable insights into important subjects as the baryon asymmetry of the Universe and lepton flavor universality, while also setting constraints on various interactions that extend beyond the Standard Model.
The primary focus of this presentation lies in exploring exotic atoms and their recently uncovered connections with superfluid helium (SFHe), that paves the way to new experimental techniques.
Within the scope of our newly approved LEMING experiment at PSI in Switzerland, we aim to conduct a gravitational free fall experiment using atom interferometry of muonium. Muonium (M) is a bound system of two elementary leptons: a muon and an electron (M = μ⁺ + e⁻). The results of a gravity measurement involving M would represent the first direct measurement of gravitational interaction in the second generation of (anti)fermions, and in the absence of composite hadrons or the strong interaction.
To lay the foundation for this experiment, we have pioneered a novel technique for producing a cold, high-luminosity atomic beam of M. The method is based on muon conversion within superfluid helium and a subsequent vacuum extraction, where we utilise the unusually high mobilities and positive chemical potentials of M in SFHe to form a high quality atomic beam. This new atomic beam also paves the way for sub-kHz precision laser spectroscopy of M, and has the potential to develop low energy, high-luminosity muon beams.
Hadronic exotic atoms immersed in superfluid He were also found to exhibit intriguing behaviors, based on our laser spectroscopy studies of antiprotonic helium at CERN and pionic helium at PSI. After generating these atoms within the quantum liquid, we observed unusually narrow atomic transitions, which pointed to a significant suppression of classical collisions. The narrow atomic linewidths renders these exotic atoms suitable for precision detection of microscopic interactions with the quantum liquid and various precision measurements, which will be briefly introduced.
Host: Jack Harris