[en] The XXVth Rencontre de Moriond was held in 1990 in Les Arcs, Savoie (France). The main purpose of this meeting is to discuss recent developments in contemporary physics, in the field of elementary particle physics, as the new particle searchs from beyond the standard model, the structure functions, the multiparticle final states, and the correlated-particle models

[en] We summarize production properties of the W and Z bosons as seen in their leptonic decay modes at the CDF Detector, using data from the 1988-89 run. Results on the masses, widths, production cross sections, P_t distributions, and limits on heavy vector bosons are presented. (data)

[en] We report on a precise study of the x and Q² dependence of the proton deuteron and neutron structure functions. In particular R = σ_L/σ_T, F_2p, F_2d, and the ratio F_2d/F_2p were extracted in a combined analysis of SLAC deep inelastic electron scattering experiments. Data from eight experiments were radiatively corrected with a new improved radiative correction formalism, and all experiments were normalized to the precise data of SLAC E140, thus yielding a single coherent data set. We find that R_p = R_d as expected from QCD. The results for R are somewhat larger than the prediction of QCD with target mass effects, thus indicating the existence of additional dynamic higher twist effects. Using both SLAC and CERN data, we obtained a parametrization of R in the range 0.5< Q²<200 GeV/c² and 0.1< x<0.86. This fit in conjunction with the normalized hydrogen and deuterium cross sections was used to extract precise values of F₂. These data provide a constraint at low Q² for high Q² muon and neutrino experiments. A study of the Q² dependence of the ratio of deuteron and proton structure functions shows a slope which is consistent with QCD and explains the difference in this ratio between SLAC and CERN experiments. (data)

[en] We present the preliminary results of a QCD analysis of the high statistics BCDMS and SLACF₂ data on D₂ and H₂. At high Q² the data are in good agreement with the predictions of perturbative QCD and lead to an improved measurement of Λ_QCD. At lower Q², a precise measurement of non-perturbative effects (higher-twists) is obtained: they are very small below x = 0.40 and small, positive and increasing with x at higher x

[en] An attempt is made to summarize the content of the about eighty papers presented at, and of the accompanying discussion during, the Moriond Meeting held on 11 - 16 March 1990

[en] One of the most striking predictions of parton picture is the development of jets in high-energy multi-hadron production. The quantitative understanding of the shape of the particle flow in a jet is possible in double-logarithm approximation in QCD. In this talk, I shall discuss two quantities. One is the angular distribution of hadrons in a jet, and the other the thrust in e⁺e^- annihilation. An interesting aspect in the analysis of the former quantity is the hypothesis of local parton-hadron duality. The value of the collinear cutoff, which is found to be strikingly small to fit the theoretical prediction to experimental data, supports the hypothesis. The thrust distribution, on the other hand, is very insensitive to the cutoff. It depends only on the ratio of the total energy and Λ_QCD and is sharply peaked at small 1-T. In addition, the additivity of invariant mass, which is positive definite, allows us to incorporate higher-order corrections easily. It thus provides an ideal means to determine the value of Λ_QCD experimentally

[en] We review some properties of QCD coherence that can be tested at LEP. In particular we discuss the following three topics: (1) Soft hadron distributions in QCD jets; (2) Properties of heavy flavour jets; (3) QCD drag effect in interjet hadron flows. 3 figs

[en] We show that the recently observed intermittency phenomenon in hadronic collisions is a consequence of short-range correlations. With the assumption of a linked-pair structure for the higher-order correlations, we find excellent agreement with the NA22 and UA5 data. We also show that the linked-pair ansatz is supported by the data regardless of the functional form of the two-particle correlations. At very high energies, in the region of large rapidity, we find a power-law behavior for the moments that is related to the self-similar pattern of multiparticle production. We give predictions for the slopes of the moments at Fermilab energies. (data)

[en] The L3 detector at LEP measured about 18,000 hadronic Z⁰ decays in 1989. Analysing these events the following results are obtained: - The Monte Carlo program JETSET describes the data well. - The multijet rates are consistent with a strong coupling constant α_s = 0.12...0.14 at √s = 91 GeV [preliminary]. - The measured neutral pion spectrum agrees with the x_p distribution of charged particles [preliminary]. - The average fractional energy of b hadrons is determined to < x_E> = 0.69 ± 0.04

[en] Experiment E769 at Fermilab obtained charm data during the 1987-88 Fixed Target running period with a 250 GeV tagged hadron beam incident on thin target foils of W,Cu,Al, and Be. From analysis of 25% of the recorded 400M trigger sample we have explored the Feynman x, p_t² and the atomic number dependence of charm quark production for D⁺ and D⁰ mesons