[en] Annihilation cross sections of antiproton-proton into hadronic channels are studied and related experimental data are compiled. These channels constitute a high source of background to the annihilation reactions p-bar + p → l⁺ + l^-, p-bar + p → l⁺ + l^- + π⁰, used for the measurement of proton form factors in Time-like region. Pion multiplicity in final state is also analysed, since the 2 neutral or charged pion production is expected to be an important issue in the detection of the leptons pair.

[en] An extension of the QED 'return to resonance' mechanism to light-meson emission (π, ρ) in (anti)proton collisions with a hadronic target (nucleon or nucleus) is proposed. The cross section and the multiplicity distributions are calculated. The collinear emission (along the beam direction) of a charged meson may be used to produce high-energy (anti)neutron beams. Possible applications at existing and planned facilities are considered.

[en] Proton elastic scattering from electrons at rest is calculated in the Born approximation. The interest of this reaction is related to the possibility of polarizing high energy antiproton beam and to high energy proton polarimetry. The differential cross section and polarization observables have been derived assuming one photon exchange. Numerical estimates are given for the cross section and the spin correlation coefficients in a wide kinematical range.

[en] Large samples of Λ, Σ(1385) and Ξ(1321) hyperons produced in the deep-inelastic muon scattering off a ⁶LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of Σ(1385)⁺, Σ(1385)^-, anti Σ(1385)^-, anti Σ(1385)⁺, Ξ(1321)^-, and anti Ξ(1321)⁺ hyperons decaying into Λ(anti Λ)π were measured. The ratios of heavy-hyperon to Λ and heavy-antihyperon to anti Λ were found to be in the range 3.8 % to 5.6 % with a relative uncertainty of about 10 %. They were used to tune the parameters relevant for strange particle production of the LEPTO Monte Carlo generator. (orig.)

[en] Multiplicities of charged hadrons produced in deep inelastic muon scattering off a ⁶LiD target have been measured as a function of the DIS variables x_Bj, Q², W² and the final state hadron variables p_T and z. The p_T² distributions are fitted with a single exponential function at low values of p_T² to determine the dependence of left angle p_T² right angle on x_Bj, Q², W² and z. The z-dependence of left angle p_T² right angle is shown to be a potential tool to extract the average intrinsic transverse momentum squared of partons, left angle k _{perpendicularto}² right angle, as a function of x_Bj and Q² in a leading order QCD parton model. (orig.)

[en] Azimuthal asymmetries in semi-inclusive production of positive (h⁺) and negative hadrons (h^-) have been measured by scattering 160 GeV muons off longitudinally polarised deuterons at CERN. The asymmetries were decomposed in several terms according to their expected modulation in the azimuthal angle φ of the outgoing hadron. Each term receives contributions from one or several spin and transverse-momentum-dependent parton distribution and fragmentation functions. The amplitudes of all φ-modulation terms of the hadron asymmetries integrated over the kinematic variables are found to be consistent with zero within statistical errors, while the constant terms are nonzero and equal for h ⁺ and h ^- within the statistical errors. The dependencies of the φ-modulated terms versus the Bjorken momentum fraction x, the hadron fractional momentum z, and the hadron transverse momentum p_h^T were studied. The x dependence of the constant terms for both positive and negative hadrons is in agreement with the longitudinal double-spin hadron asymmetries, measured in semi-inclusive deep-inelastic scattering. The x dependence of the sin φ-modulation term is less pronounced than that in the corresponding HERMES data. All other dependencies of the φ-modulation amplitudes are consistent with zero within the statistical errors. (orig.)

[en] Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality Q"2 > 1 (GeV/c)"2. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam impinging on a polarised "6LiD target. By analysing the full range in hadron transverse momentum p_T, the different p_T-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation Δg/g is evaluated at leading order in pQCD at a hard scale of μ"2 = left angle Q"2 right angle = 3 (GeV/c)"2. It is determined in three intervals of the nucleon momentum fraction carried by gluons, x_g, covering the range 0.04 < x_g < 0.28 and does not exhibit a significant dependence on x_g. The average over the three intervals, left angle Δg/g right angle = 0.113 ± 0.038_(_s_t_a_t_._) ± 0.036_(_s_y_s_t_._) at left angle x_g right angle ∼ 0.10, suggests that the gluon polarisation is positive in the measured x_g range. (orig.)

[en] The COMPASS Collaboration at CERN has investigated the reaction π^-γ → π^-π^-π⁺ embedded in the Primakoff reaction of 190 GeV pions scattering in the Coulomb field of a lead target, π^-Pb → π^-π^-π⁺ Pb. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at momentum transfer below 0.001 (GeV/c)². Using a partial-wave analysis the amplitudes and relative phases of the a₂(1320) and π₂(1670) mesons have been extracted, and the Coulomb and the diffractive contributions have been disentangled. Measuring absolute production cross sections we have determined the radiative width of the a₂(1320) to be Γ₀(a₂(1320) → πγ) = (358 ± 6_stat ± 42_syst) keV. As the first measurement, Γ₀(π₂(1670) → πγ) = (181 ± 11_stat ± 27_syst) keV . (BR^PDG_f2π/BR_f2π) is obtained for the radiative width of the π₂(1670), where in this analysis the branching ratio BR^PDG_f2π = 0.56 has been used. We compare these values to previous measurements and theoretical predictions. (orig.)