Experimental Apparatus for Antiproton-Nucleus Annihilation Cross Section Measurements at Low Energy

The antiproton annihilation cross section at 5.3 MeV of kinetic energy on different nuclei (Ni, Sn, Pt) has been recently measured by the ASACUSA Collaboration at the CERN Antiproton Decelerator. A new experiment with a different apparatus has been performed on a carbon target in order to get a more precise measurement for a stringent comparison with the antineutron data. Thin foils (∼700–1000 nm) of carbon have been put in a vacuum chamber and the bunches of ∼10^7 antiprotons provided by the AD crossed them. Some of the antiprotons are expected to annihilate on the protons or neutrons of the carbon nucleus and the charged particles emitted in the process (mainly π^±s) are detected using segmented scintillators. Some other antiprotons are scattered by Coulomb force towards the vessel lateral surface generating a background contribution of the measurements. The above mentioned events occur every AD extraction cycle (120 s) in a time window of about 50 ns, putting several constraints on the detectors and the DAQ system. We here describe the details of the apparatus needed to perform this measurement.