Pion correlations and resonance effects in $$\bar pp$$ annihilation at rest to 2π+2π-π0

Abstract

We study ππ correlations in the exclusive reaction $$\bar pp \to 2\pi ^ + 2\pi ^ - \pi ^0 $$ at rest with complete reconstruction of the kinematics for each event. Inclusive and differential distributions properly normalized show an enhancement for small invariant masses M ++,M -- of like-pion pairs. An even stronger enhancement is seen for the double differential distributions for low pion-pair masses. The signal is strongest when the π0 energy is large and much weaker when this energy is small. Dynamical models with resonances in the final state are confronted with the data. For the kinematic situation where the ρ3π channel is important the simulation predicts a large pion correlation for the double differential density, qualitatively explaining the observed bahaviour. The stochastic HBT mechanism is not supported by these findings for the exclusive annihilation reaction studied.