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We present results obtained in π A ( A=C, Cu, Pb) - collisions at 38 GeV/c. A single particle trigger selects events with one charged particle in the central region and large transverse momentum. The effect of this trigger on the multiplicities of all charged particles and of protons is shown. [ABSTRACT FROM AUTHOR]

Interactions of 40 GeV/c π, K and $$\bar p$$ on Li, C, S, Cu, CsI and Pb were studied with the RISK-streamer chamber spectrometer. We present multiplicities of negatively charged particles, as well as of protons, and the correlations between them. The normalized mean multiplicity of negative particles, R, depends on $$\bar v$$ , the average number of inelastic collisions as $$R^ - = (0.73 \pm 0.04) + (0.34 \pm 0.02)\bar v$$ . The dependence of the normalized dispersion of negative particles, D/< N>, on the number of protons favours independent collision models and contradicts the coherent tube picture. The excess of fast positive particles behaves as A and shows, for the heavier nuclei, a clear correlation with identified protons. [ABSTRACT FROM AUTHOR]

The π p interactions with at least one charged secondary produced at polar angle ∼90° in c.m.s. and having the transverse momentum above 1 GeV/c were investigated. The data were obtained using streamer chamber magnetic spectrometer RISK at 38 GeV/c π beam from Serpukhov accelerator. The analyzis of associated production in reconstructed events suggests, that if the transverse momentum of a pair of oppositely charged secondaries compensates the trigger particle p practically completely, this pair is the product of the ρ decay in marked fraction of such events. We observed a large spin-alignment for the ρ-mesons selected as described above: the probability of zero spin projection onto the normal to the ρ production plane is equal to ρ=0.86±0.23. The enhancement of the number of events, in which the ρ picks up practically full momentum transfer carrying by the exchange, and also the enlarged tensor polarization for the ρ-mesons in these events could be qualitatively explained as manifestation of direct ρ-production via the QCD higher twist processes in the high pπ p collisions. At the same time, the observed effects are markedly larger than the values predicted with QCD model in which the higher twist corrections were included. [ABSTRACT FROM AUTHOR]

Measurements of K, Λ and $$\bar \Lambda $$ production in π nucleus (C, Cu, Pb) interactions are presented. The experiment was carried out with the streamer chamber spectrometer RISK using a π beam of ∼40 GeV/c and a trigger requiring a secondary charged particle with transverse momentum above 1.1 GeV/c. Production cross sections, relative production rates and distributions of Feynman x and transverse momentum squared as well as correlations between the V and the trigger particle are presented. The results are compared and found to be in agreement with K, Λ and $$\bar \Lambda $$ data from untriggered π p and π C interactions, except for the relative production rate of antilambdas which is about to times larger in high- p collisions. Our results can be well interpreted within the dual topological unitarization model. [ABSTRACT FROM AUTHOR]