GSI/FAIR directors visit WASA detector setup at the fragment separator FRS


“It is very impressive to see how such a large collaboration of international scientists works together and I am impressed by the great scientific achievements”, says Professor Paolo Giubellino, the Scientific Managing Director of GSI and FAIR. Together with his colleagues Jörg Blaurock and Dr. Ulrich Breuer, the Technical Managing Director and the Administrative Managing Director of GSI and FAIR, he visited the WASA detector, which is presently installed at the GSI fragment separator FRS, a few days after the successful commissioning of the experiment in February and March 2022. All three directors wanted to obtain first-hand information of this milestone experiment and get a direct impression of the ongoing work and its first results.

In the meantime, several experiments have been performed successfully to search for and study very special exotic atoms, especially mesic atoms and hypernuclei. The experiments build on a long-standing and intense collaboration between GSI and RIKEN, Japan's largest comprehensive research institution renowned for high-quality research in a wide range of modern scientific disciplines.

Regular atomic nuclei are made of protons and neutrons, which in turn are composed of a total of three up and down quarks. They form the nucleus and, together with the surrounding electrons, an atom. If one of the quarks in the nucleus is replaced by another type, a so-called strange quark, a hypernucleus is formed. Hypernuclei can be produced in energetic particle collisions at accelerators, and their decay can be observed in experiment setups such as the WASA detector and the FRS in order to study their properties in detail. They are particularly interesting because current theories expect them to determine important properties of neutron stars. In a similar way, an exotic atom can be formed if electrons in the surrounding atomic shells of nuclei are replaced by other charged particles, like for instance a meson. A meson is an unstable pair of a quark and an antiquark. Studying these exotic atoms could provide a hint to understanding the origin of the mass of matter in the universe. WASA@FRS allows to produce and study such exotic, very rare systems with very high experimental sensitivity and purity.

While the FRS is largely used for the separation and identification of exotic nuclei, the Super-FRS Experiment Collaboration takes advantage of its high momentum-resolution capabilities, which are unique in the world in the domain of relativistic proton and heavy-ion beams, thus allowing for unrivalled particle physics studies. The combination of a high-resolution momentum spectrometer with the “Wide Angle Shower Apparatus” WASA, which is designed to trace the tracks of large numbers of particles emitted in energetic nuclear collisions, opens a door to unprecedented experimental opportunities at the border line of atomic, nuclear and hadron physics.

The present experiments serve as pilot study for even further advanced science goals at the Super-FRS of FAIR, which is presently under construction. “The WASA research activities are largely driven by Japanese scientists. The cooperation with Japanese research institutions has been extremely valuable for GSI and we hope for an intensified continuation of this fruitful collaboration in the future”, says Paolo Giubellino. (CP)