When it comes to describing the fundamental structure and composition of matter, the research field of quantum chromodynamics (QCD) comes into play. With the help of QCD, the strong interaction—one of the four fundamental forces of physics—between the elementary particles of quarks and gluons can be described in hadrons. Hadrons are subatomic particles held together by the strong interaction. The best-known examples are neutrons and protons (so-called baryons), and the lesser-known pion (a so-called meson) is also a hadron. "To a first approximation, the pions are the driving particles behind the strong interaction," says the physicist Urs Wenger, professor at the Institute for Theoretical Physics at the University of Bern.