Cross-beam atomic collision experiment between ultra-low-energy antiprotons and a supersonic gas jet

The antiproton is a unique projectile in the study of atomic collision physics. With an aim to produce an antiproton beam at atomic-physics energies for ‘pure’ collision experiments, we have so far developed techniques to decelerate, cool and confine antiprotons in vacuo. Our recent success in stable extraction of the beam has opened up the possibility to study ionization and atomic capture processes between an antiproton and an atom at an unprecedented low energy from 10 eV to 1 keV under the single-collision condition. We have prepared a powerful supersonic helium gas jet to be crossed with the antiproton beam. The reaction rate is of the order of 10^???4, and rigorous identification of particles is required for reduction of huge background counts. The reaction events are recognized by an electron signal followed by antiproton annihilation with an appropriate interval in the time of flight. Our design and strategy of the experiment are presented.