Yu. A. Golubkov

Possible manifestations of the existence of a fourth-generation neutrino

A fourth generation of fermions predicted by the phenomenological heterotic string models can possess a new, strictly conserved charge. Among other things, this leads to the hypothesis of the existence of a fourth massive stable neutrino. A comparison of this hypothesis with the data obtained in the DAMA underground experiment to search for massive weakly-interacting cosmic particles with hidden mass and with the EGRET measurements of the >1 GeV galactic gamma-ray background gives a value m≈50 GeV for the possible mass of the fourth neutrino. It is shown that the hypothesis can be checked in accelerator experiments. The positron signal from annihilation of massive relic neutrinos in the galaxy is calculated. A search for this signal is is within the reach of planned cosmic-ray investigations.

Indication of an onset of hard-like effects in K+p, π+p and pp collisions at 250 GeV/c: EHS/NA22 Collaboration Aachen-Antwerp/Brussel-Berlin (Zeuthen)-Helsinki-Cracow-Moscow-Nijmegen-Rio de Janeiro- Serpukhov-Warsaw-Yerevan

Abstract Similarly as in lepton-hadron scattering, but less pronounced than in e + e − annihilation at comparable energies, we observe a rise of the “sea-gull” wings with CMS energy. The large average transverse momenta around Feynman | x F |=0.4 are mainly due to high multiplicity events, for which also a tail develops in the multiplicity distribution. Neither of these effects can be reproduced by currently used low- p T fragmentation models.

Multiplicity distribution inK+ Al andK+ Au collisions at 250 GeV/c and a test of the multiple collision model

Multiplicity distributions, observed inK+ interactions with Al and Au nuclei at 250 GeV/c incident momentum are presented. They are analyzed in the framework of multiple collisions of the incident particle inside a nucleus. The probability distribution of the number of grey tracks is well described by the model of Andersson et al., if a negative binomial distribution is assumed for the distribution of the number of grey protons produced per elementary collision instead of the usual geometrical distribution. The analysis of the average and dispersion of the charge multiplicity distribution supports the validity of the multiple collision model, including results on correlations between forward and backward multiplicities.

Strange and non-strange baryon production in π+p andK+p interactions at 250 GeV/c

AbstractWe present data on the production of the baryons Λ,

Negative binomials and multiplicity distributions in 250 GeV/cK+ and π+ interactions on Al and Au nuclei

\bar \Lambda

Inclusive production ofρ0 andf2 mesons in π−p interactions at 360 GeV/c

,p and of the baryon resonances Σ*+ (1385) and Δ++ (1232) inK+p and π+p interactions at 250 GeV/c. Results are given on total and semi-inclusive cross sections, Feynman-x spectra, transverse momentum distributions and Λ polarization. The data are compared with measurements at lower energies, with deep inclastic lepton nucleon data and with predictions of quark-parton models. The models underestimate Λ production in the central c.m. region, a feature also seen in recent heavy-ion data. This failure can be cured in JETSET 6.3 by adjustment of the di-quark break-up probability.

Collective characteristics of hadron systems produced in beam fragmentation of π+p collisions at 250 GeV/c

A model is developed for antimatter loss by a globular cluster of antimatter stars and its annihilation with a gas of ordinary matter. The flux of photons produced in proton-antiproton annihilation is shown to reproduce the observed γ background measured by the EGRET telescope. The maximum possible number of antimatter stars presumably existing in the Milky Way Galaxy is estimated on the basis of a comparison with observational data.

An impact parameter analysis of proton-proton elastic and inelastic interactions at 360 GeV/c

The negative binomial distribution (NBD) is fitted to all charged and to negative particle multiplicity distributions in restricted rapidity intervals, both in the forward and backward c.m. hemispheres of positive meson interactions on Al and Au nuclei. For negative particle multiplicity distributions, the NBD parameters are also determined as a function ofng, the number of grey tracks, corresponding to varying number of intranuclear collisions. The data are interpreted in terms of the clan picture of Giovannini and Van Hove and compared to the MCMHA and Fritiof models. Both models reproduce quite well the global multiplicity distributions, but not when sub-samples are considered with fixed number of grey tracks. Regularities are better visible on the parton than on the particle level.