Evidence for the formation of a highly excited hadronic blob in antiproton-4He annihilation

The production of charged kaons in p¯ 4He annihilation at rest into four and five charged prongs (π±π−π+K∓, 2πK−K+ with and without an additional proton with momentum >300 MeV/c) is studied experimentally. Annihilations with and without π0 production and with baryonic number B = 0 and B >= 1 are identified. The data on He are compared with similar data obtained on a hydrogen NTP gas target with the same apparatus (the magnetic spectrometer Obelix exposed to the p¯ beam extracted from the LEAR accelerator at CERN) and analyzed with the same criteria. Strangeness production on 4He from B >=1 annihilations without π0 turns out to be six times higher than on hydrogen. Our results agree with some theoretical predictions based on the assumption that annihilation develops through the formation and the statistical decay of a highly excited hadronic gas. According to these predictions, nearly all nucleons in He are directly involved in the annihilation process.