Long-lived pionic helium: Exotic matter experimentally verified for the first time

Exotic atoms, in which electrons are replaced by other subatomic particles of the same charge, allow deep insights into the quantum world. After eight years of ongoing research, a group led by Masaki Hori who is a senior physicist at the Max Planck Institute of Quantum Optics in Garching, Germany, now succeeded in a challenging experiment: in a helium atom they replaced an electron with a pion in a specific quantum state and verified the existence of this long-lived “pionic helium” for the very first time. The usually short-lived pion could thereby live a thousand times longer than it normally would in other varieties of matter. Pions belong to an important family of particles that determine the stability and decay of atomic nuclei. The pionic helium atom now enables scientists to study pions in an extremely precise manner with the means of laser spectroscopy. The research is published in this week’s edition of Nature.