A search for QGP formation in antiproton-4He annihilation at rest

The dependence of the strangeness production on the number of nucleons involved in the annihilation process is investigated experimentally in p¯p and p¯4He annihilation at rest. In He, annihilations with the involvement of one and several nucleons (B=0 and B⩾1 baryonic number, respectively) are identified. Strangeness enhancement factors, i.e., ratios of K±, KS0, K0∗ and ϕ meson yields in 4He to the same yields in H, are derived for final states containing 4 charged mesons (2π+2π−, π+π−π∓K±, π+π−K+K−). This work completes a previous investigation concerning charged kaon production in meson final states without neutral mesons. The results are compared with our previous ones and with results found in experiments on heavy-ion collisions. It is put in evidence that the strangeness content in the energy blob created by the annihilation has a lower or higher intensity depending on the reaction channel: for instance, π+π−π∓K± production increases with B and π+π−K+K− production decreases. The maximum enhancement factor (about 22) is found for π+π−π−K+ without neutral mesons. This value (as well as that concerning π+π+π−K−) is definitely higher than the values predicted by theoretical investigations based on the formation of a highly excited hadronic gas in the annihilation on few nucleons and values found in heavy-ion collisions. Is it the signature of the formation of quark-gluon plasma?