Eur. Phys. J. C (1999) 6: 437-450
https://doi.org/10.1007/s100529801032

Pion correlations and resonance effects in annihilation at rest to 2π+2π-π⁰

¹ University of Athens, Greece
³ University of Basle, Switzerland
¹⁰ Boston University, USA
⁷ CERN, Geneva, Switzerland
¹⁷ Theory Group F1, Paul Scherrer Institut (PSI), Villigen, Switzerland
¹⁴ Delft University of Technology, Netherlands
⁶ University of Fribourg, Switzerland
¹⁵ University of Ioannina, Greece
⁹ University of Liverpool, UK
¹³ J. Stefan Inst. and Phys. Dep., University of Ljubljana, Slovenia,
² CPPM, Université d’Aix-Marseille II, IN2P3-CNRS, France
¹⁶ CSNSM, IN2P3-CNRS, Orsay, France
⁴ Paul Scherrer Institut (PSI), Villigen, Switzerland
¹¹ CEA, DSM/DAPNIA, CE-Saclay, France
⁸ Royal Institute of Technology, Stockholm, Sweden
¹² University of Thessaloniki, Greece
⁵ ETH-IPP Zürich, Switzerland

Received: 4 June 1998
Accepted: 6 November 1998
Published online: 6 November 1998

Abstract

We study ππ correlations in the exclusive reaction 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.