The angular distribution of the inclusive reaction 4 He + p → 3 He + X was measured with 6.85 GeV/ c incident alphas. At large angles, the observed kinematics corresponds to the elastic scattering on the target proton of an 3 He present in the incoming 4 He, the remaining neutron being a spectator. This shows the presence of an important component of 3 He in 4 He. The integrated cross section for 3 He production is σ 3He = 24.1 ± 1.9 mb.
In this paper we report measurements of the backward K−p differential cross section at 49 momenta covering the momentum range 476-1084 MeV/c. The statistical precision achieved, typically 2.5%, is an order of magnitude better than previous measurements. The systematic errors for this reaction are about 1%. The differential cross section for the reaction K−p→Σ−π+ where the π+ emerges at 0° has also been measured at 32 momenta with comparable improvement in precision over previous experiments. A partial-wave analysis of the K¯N channels including the new K−p backward elastic data is presented.
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The double-differential cross sections for high-energy γ-rays were measured for collisions of 36Ar on C, Al, Cu, Ag, Tb, and Au at 85 MeV/nucleon. The system 36Ar+ 27Al has been studied in more detail in an exclusive experiment where the charged-particle multiplicity was measured in coincidence with high-energy γ-rays. A clear correlation between the hardness of the γ-spectra and the overlap distance of the two ions is observed. This correlation is interpreted as due to the spatial dependence of the Fermi momentum of the nucleons.
The inclusive production of Ks0, Λ, Λ¯, and Ks0Λ in the p¯Ta reaction at 4 GeV/c was measured and compared with that in the p¯p reaction. The total inelastic and topological cross sections were also measured. The number of Λ’s produced in the p¯Ta reaction was 11.3 times larger than that expected from the geometrical cross section, which is defined as A2/3 times the cross section for the p¯p reaction. The yield ratio Λ¯/Λ was found to be 2×10−2. These values cannot be accounted for by a straightforward extension of the p¯N reaction. Besides, a correlation of 2 vees like Ks0-Λ could not prove their simultaneous production. Nuclear temperatures of 135 and 97 MeV were obtained from the kinetic energy spectra of Ks0 and Λ, respectively. The kinematical characteristics of the Ks0 and Λ produced were analyzed in terms of the fireball model.
The missing-mass technique has been used to study the spectra of neutral mesons produced by 2- and 3-Gev protons in the reaction p+d→He3+x0. Cross sections (dσdΩc.m.) of about 10−34 cm2/sr were observed for the π, η, and ω for 3-GeV protons. A peak with a much smaller cross section was observed at a mass of 956 MeV. We have tentatively identified this peak as the η′. Cross sections for the π and η were nearly a factor of 10 larger at 2 GeV than at 3 GeV. Deviations from simple phase space were observed near the two-pion threshold in both 2-GeV and 3-GeV data. Details of the experimental method and of the results are presented.
The differential cross sections for Bhabha scattering and μ pair production, and the total τ pair cross section as measured by the PLUTO detector at PETRA, have been analyzed to extract information on the weak interaction of leptons. The data are compared with unified gauge theories. Since the observed electroweak effects are still consistent with zero (within errors) we can set experimental limits on neutral current parameters atQ2 values of 950 GeV2. In the framework of the standard SU(2)×U(1) model we find sin2Θw<0.52(95% c.l.). In the context of general singleZo models we can excludeZo masses of less than 40 GeV.
Double differential cross sections have been measured for pi+ and K+ emitted around midraidity in d+A and He+A collisions at a beam kinetic energy of 1.15 GeV/nucleon. The total pi+ yield increases by a factor of about 2 when using an alpha projectile instead of a deuteron whereas the K+ yield increases by a factor of about 4. According to transport calculations, the K+ enhancement depends both on the number of hadron-hadron collisions and on the energy available in those collisions: their center-of-mass energy increases with increasing number of projectile nucleons.
Inclusive π − spectra have been measured for 14 N+C collisions at 41 A , 67 A , 80 A and 135 A MeV, the lowest energies measured for the charged pion. The cross sections fall exponentially with T π and the exponential slope factors at 90° in the nucleon-nucleon center of mass frame are determined. Energy distributions below a beam energy of 100 A MeV are less steep than expected from the monotonic decrease of the slope factor down to 100 A MeV. The production mechanism of energetic pions far below threshold is discussed for several models.
The cross section for the production of $\omega$ mesons in proton-proton collisions has been measured in a previously unexplored region of incident energies. Cross sections were extracted at 92 MeV and 173 MeV excess energy, respectively. The angular distribution of the $\omega$ at $\epsilon$=173 MeV is strongly anisotropic, demonstrating the importance of partial waves beyond pure s-wave production at this energy.
Measured cross sections for omega production.
Angular distribution of the OMEGA in the overall centre-of-momentum frame. Statistical error only.
Cross sections were determined in the Δ(1232) excitation region for the reactions 3 He( γ , π + ) 3 H, 3 He (γ, π + ) nd,nnp and 3 He (γ, π − ) ppp at several photon energies and pion emission angles. Inclusive charged-pion photoproduction spectra were measured with a magnetic spectrometer using quasi-monochromatic positron-annihilation photons. Quasi-free mechanisms have been clearly observed, but pion-nucleon and nucleon-nucleon rescattering and Pauli exclusion mechanisms must be considered to explain the trend of the data for the different channels.
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