Quark deconfinement in antiproton annihilation at rest on light nuclei

We experimentally investigated the dependence of the K + and K − production on the number of nucleons involved in the annihilation process at rest on 3 He and 4 He gas targets comparing the results with \(\overline p^1H\) and \(\overline p^2H\) annihilation data: all events were collected by the Obelix experiment, in operation at LEAR until 1996. Events with and without production of neutral mesons and with and without emission of fast neutrons (that is neutrons involved in the annihilation process) are recognized. The results are consistent with our previous ones on a more restricted sample of annihilation reactions on 4He and put in evidence that the strangeness production is lower or higher depending on the reaction channel. As a general trend, the strangeness production is higher in events with the involvement of a higher number of nucleons. The maximum K + production is observed in the reaction \(\overline p ^4He \rightarrow K^+ 2\pi^+ 2\pi^- 3n\) (with the involvement of 3–4 nucleons): compared with the reaction on hydrogen \(\overline p p \rightarrow K^+ 2\pi^+ 2\pi^- \) the production on 4He is higher by a factor of 31.7 ± 5.5. In the light of some theoretical speculations this enhancement is too high to be explainable in terms of hadronic interactions and could be interpreted as a signature of quark deconfinement or possibly of QGP formation.