Influence of multiplicity and kinematical cuts on Bose-Einstein correlation inπ + p at 250 GeV/c

The correlation of negative particles at small momentum difference and its dependence on multiplicity and on kinematical cuts is studied in π+p-interactions at 250 GeV/c. In terms of the Kopylov-Podgoretskiį parametrization, an average radius of the pion emitting region ofrK=1.59±0.14 fm and a life-time (or emission depth) τ=0.83±0.25 fm are found. The Lorentz invariant parametrization of Goldhaber givesrG=0.85±0.04 fm. Assuming two different sources of pions, their radii are estimated asr1=1.75±0.25 fm andr2=0.60±0.08 fm. An angular and multiplicity dependence of the space-time size of the source is observed. The source is elongated along the collision axis and has larger sizerK at higher multiplicities. The radiusrK decreases with increasing pion pair momentum. The size of the emitting region appears to be larger for low rapidity pions than for pions from the fragmentation region. No evidence is found for a unique reference frame, where the pion source is motionless for each π+p collision, i. e. where the space-time size of the source is definitely smaller than in any other frame