Eur. Phys. J. C (1998) 1: 139-148
https://doi.org/10.1007/BF01245804

Direct determination of two-pion correlations for pp→ 2π⁺2π⁻ annihilation at rest

¹ University of Athens, Greece
³ University of Basle, Switzerland
¹³ Boston University, USA
⁸ CERN, Geneva, Switzerland
¹⁰ LIP and University of Coimbra, Portugal
¹⁶ Delft University of Technology, Netherlands
⁷ University of Fribourg, Switzerland
¹⁴ University of Ioannina, Greece
⁶ University of Liverpool, UK
¹⁵ J. Stefan Inst. and Phys. Dep., University of Ljubljana, Slovenia
² CPPM, IN2P3-CNRS et University d'Aix-Marseille II, Marseille, France
¹⁸ CSNSM, IN2P3-CNRS, Orsay, France
⁴ Paul Scherrer Institut (PSI), Villigen, Switzerland
¹² CEA, DSM/DAPNIA CE-Saclay, France
⁹ KTH-Stockholm, Sweden
¹¹ University of Thessaloniki, Greece
⁵ ETH-IPP, Zürich, Switzerland
¹⁷ Theory Gruop Fl, Paul Scherrer Institute (PSI), Villigen, Switzerland

Received: 24 September 1997
Published online: 27 February 2005

Abstract

We study ππ correlations in the exclusive reaction pp → 2π⁺2π⁻ at rest measured by the CPLEAR experiment. Avoiding the introduction of an arbitrary reference sample, we analyse differential distributions for equal charge pion pairs removing the phase-space factor event by event. A peak at small relative momenta is most pronounced for large total momentum of the pair. The physical implications of bosonic symmetrization for the properties of the pion source, in particular its radius, are briefly discussed. The two extremes considered are the chaotic Hanbury-Brown-Twiss mechanism and the coherent Skyrmion model.