Influence of resonances on Bose-Einstein correlations of identical pions

The influence of resonances on narrow pair correlations of identical pions is considered in detail. It is shown that kinematic or dynamic restrictions on resonance momenta lead to a substantial anisotropy of the correlation function; variables allowing one to reveal this anisotropy are proposed. An upper estimate of 0.23 for the fraction of directly produced pions is obtained based on experimental data on the resonance yields in high-energy hadron interactions. It is shown that experimental data on like-pion correlations agree with a dominant contribution of the pions from the decays of light resonances. In particular, the observed value of the parameter characterizing the suppression of the interference effect, the decrease of the slope of the correlation function with increase in the relative momentumQ of the like pions in their c.m.s. and the dependence of the time parameter on the pion velocity are explained. It is shown that the slope of the correlation function for the like-pion pairs containing the decay pions atQ>0.1 GeV/c is mainly determined by the size of the resonance production region, which allows one to determine the size of the production region of direct particles (pions and resonances) despite the very low fraction of the pairs of directly produced pions. The fraction of directly produced pions, 0.17±0.09 (stat.)±0.08 (syst.), and the radius of the direct production region, 0.55±0.08 (stat.)±0.10 (syst.) fm, have been determined based on the analysis of the most accurate correlation function measured inpp- and -interaction on ISR at 63 GeV.