Search

Bose-Einstein correlations up to fourth order are presented at . Genuine third-order correlations are observed. The experimental data are compared with predictions from a quantum statistical approach of radiation from a partially coherent source and with the FRITIOF model.

Backward proton production is studied in interactions of p+ andK+ mesons withAl andAu nuclei at 250 GeV/c. The proton momentum spectra are measured at different emission angles. From the two-proton correlations, it is found, that a significant part ((26±4)% forAl and (44±6)% forAu) of the backward proton production can be attributed to secondary pion absorption by a nucleon pair in the nuclear medium, and . It is found that the share of the secondary pion absorption can be fitted by a power dependence aAß, with ß=0.27±0.05. An upper limit of the cross section for the colour-charge-exchange mechanism of backward proton production is estimated.

The angular dependence of Bose-Einstein correlations is studied in interactions of p+ andK+ mesons with protons and nuclei at 250 GeV/c. The pion source is found to be elongated along the interaction axis in the c.m.s., with the ratioa between transverse and longitudinal dimension equal to 0.55±0.06 for the case of proton, 0.53±0.13 for the case ofAl and 0.33±0.21 for the case ofAu target. For meson-proton interactions, indication for an increase of the elongation is found with increasing event multiplicity, pair momentum and particle transverse momentum.

The production properties ofKs0, andK+p interactions at 32 GeV/c are investigated using the final statistics of the experiment. We present total and semi-inclusive cross sections and aver-age multiplicities. Estimates are given of the diffractive dissociation contributions to total and differential cross sections. Thex-,pT-, and transverse mass dependence of inclusive and semi-inclusive distributions is discussed as well as properties of “prompt”Ks0's. The ratio of “prompt”K890+ (K8900) to “prompt”K0 cross sections is measured to be 1.03±0.12 (0.98±0.17). From a comparison of production inK±p interactions at 32 GeV/c, we estimate a strange sea-quark suppression of 0.26 ±0.02. The double differential cross sections ofKs0's is studied as a function of Feynman-x andpT2, and a Triple-Regge fit performed. The data are compared in detail to versions of the Lund-model for low-pT hadronic collisions.

The mass spectra of theωπ0 system, produced inπ−p charge-exchange reactions at 38 GeV/c and 100 GeV/c, show a new neutral state with a mass of 2200±20 MeV and a width of 260±50 MeV. Likeρ3(1690), this meson,X(2200), is produced through one-pion-exchange.X(2200)JPC is likely 1−−. It might be a 23D1 radial-orbital excitation ofρ0. Its production cross section falls with energy quadratically, in agreement with one-pion-exchange. The cross sections forb1(1235) andρ3(1690) production have also been measured; their energy dependences have been determined.

The NA22 data onπ−π−correlations are analyzed in terms of a number of two- and three-dimensional parametrizations (Gaussian space-time, Goldhaber, Bowler string-like, Bertsch hydrodynamical, Kopylov-Podgoretskii, etc.). Contrary to the results obtained for e+e−andµp collisions, the Goldhaber parametrization, as well as string-like models, fail in describing the hadron-hadron data. Better fits are obtained in the framework of surface-emitting fireball-like models, both when including and excluding hydrodynamical expansion of nuclear matter. Our results indicate that pion radiation occurs at earlier stages of matter evolution than in nuclear collisions.

An analysis of theA-dependence of the target-diffractive cross-section is presented. Data on thet-dependence of the cross section are fitted in the usual exponential form. The mean multiplicity of negative particles produced diffractively is found not to be sensitive to the nuclear mass. TheA-dependence of the emitted proton multiplicity and the angular distributions of the produced charged particles suggest re-scattering of the emitted particles on other nucleons of the nucleus. All these facts are compared with results obtained by Monte-Carlo simulation according to a two-component Dual Parton Model.

Energy, charge and strangeness flow inK+p interactions at 32 and 70 GeV/c, and p+p interactions at 32 GeV/c are studied in terms of the angular variable ?=|x|/pT. The data ondQ/d? anddE/d? show only a weak indication of scale breaking between 32 and 70 GeV/c. For inclusive “non-diffractive”, inclusive “diffractive” and exclusive “non-diffractive” jets, the fraction of charge in any angular region ?O away from the central region is found to be proportional to the energy fraction in the same interval. The data ondQ/dE versus ? are compatible with some versions of dual-sheet models and agree also with the LUND Monte-Carlo model. The data are also compared with interactions in BEBC. In exclusive channels the average ratiodQ/dS=0.78±0.04 is consistent, in the framework of fragmentation models, with a larger probability for the fragmentation of the -valence quark than theu-valence quark in theK+-meson.