Study of antiproton nucleon annihilations at rest into five pions

The Crystal Barrel Experiment at LEAR allows the detection of charged particles and photons with almost 4π angular coverage, respectively. Here we present a study of pp annihilation and pd annihilation at rest into five-pion final states (pp→5π0, pp→π+π-3π0, pd→π-4π0pand pd→π+2π-2π0p). These reactions are well suited to look for four pion decays of scalar and vector mesons. Previous experiments on pn→2π+3π-, np→3π+2π-, and pp→π+π-3π0 established the dominance of the production of a scalar isoscalar resonance with a mass of about 1370 MeV and a width of about 350 MeV. The f0(1370) was found to have a sizeable decay branching ratio into σσ and pp. We show, in an analysis of the reaction pp → 5π0, that there is indeed a scalar resonance decaying into 4π0, but this resonance can be identified with the f0(1500), a new resonance, observed by the Crystal Barrel Collaboration in the decay modes π0π0, ηη and ηη'. In the 5π0 final state we found evidence for the f0(1500) decay to σσ and π(1300)π. A preliminary result of a combined analysis of the four five-pion data sets mentioned above confirms the existence of the f0(1500) in the data and shows that the σσ decay of the f0(1500) is more important than its decay to ρρ. (orig.)