R. Stenbacka

Cross sections of annihilation and inelastic final states for pp interactions at 9.1 GeV/c

Abstract Topological and channel cross sections are given for annihilation and inelastic final states produced in p p interactions at 9.1 GeV/c. Cross sections for prominent resonances in specific channels and charged pion, ϱ 0 and Δ ++ inclusive cross sections are also presented.

Search for single cluster formation in annihilation reactions

Single-particle inclusive data from pp annihilation experiments at 4.6 and 9.2 GeV/c are displayed, and compared with other data from NN and e+e− annihilation reactions. The single-particle distributions are found to be exponentially peaked and almost isotropic at small momenta in the centre of mass. The temperature, or exponential slope of this distribution, is well fitted by a linear form in s−12, extrapolating to an “ultimate temperature” of 164 ± 5 MeV. These results are in accordance with the hypothesis that the annihilations very often give rise to the formation of single clusters, whose decay can be described by the statistical bootstrapmodel. Attempts to isolate a class of events corresponding to single cluster formation are discussed.

Two-pion correlations in 9.1 GeV/c antiproton-proton reactions

We present a study of two-pion correlations in 9.1 GeV/c antiproton-proton reactions where both annihilation channels and non-annihilation channels are investigated. We find an asymmetry in the distribution of the azimuthal angle between the pions for different charge combinations. The variation of the asymmetry parameter B with the rapidity difference between the two pions indicates a strong short range correlation. A marked forward-backward asymmetry of the charge distribution in the c.m. system is found in the rapidity classification of the pions. The asymmetry is also found in the local ordering of the charges. In the space angle distribution there is a pronounced accumulation of event the region 0.3 < cos θπ+π− <0.8 in the 5π and 7π final states. This effect is partly explained by ϱ(770) production.

Inclusive γ, KS0 and Λ production in 4.6 and 9.1 GeV/c pp interactions

Results of the determination of the inclusive total and topological cross sections are given for the reaction pp → γ + X, π0 + X, K0 + X, and Λ + X at 4.6 and 9.1 GeV/c. We present the average number of π0, K0 and Λ as a function of the associated charge multiplicity. Invariant differential cross sections are given as a function of pT2 and x.

Inclusive production of vector and tensor mesons in antiproton-proton annihilation and non-annihilation interactions at 9.1 GeV/c

Cross sections have been determined for the inclusive production of vector (ϱ0, ω, K∗) and tensor (f, A2±) mesons in pp reactions at 9.1 GeV/c for both annihilation and non-annihilation processes. Distributions in the Feynman variable x and transverse momentum squared, pT2, have been examined for the ϱ0, ω and f mesons. The slopes for pT2 appear to be exponential and decrease with increasing particle mass for both annihilation and non-annihilation reactions, furthermore the slopes have consistently higher values for non-annihilation reactions. Comparisons with other data indicate that the ratio ϱ0/π− is independent of antiproton momentum in annihilation processes.

Study of the reaction pp → Δ++ Δ++ at 9.1 GeV/c

Single and joint decay angular distributions in the reaction pp → Δ++ Δ++ at 9.13 GeV/c are discussed in the framework of single and double statistical tensors. The t dependence of 12 double statistical tensors is presented. Cross sections for pp → ppπ+π−andpp → Δ++ Δ++ are determined to be 2.60 ± 0.10 and 0.90 ± 0.10 mb respectively. The results obtained are compared with other experiments mainly at 5.7 and 12 GeV/c.

High transverse momenta and p̄p annihilations

Abstract The pp annihilation process has a predominantly statistical character even at high energies. This has been recently demonstrated in a study of the average transverse momenta produced in various interactions. This paper presents a further study of the problem concerning the asymptotic behaviour of the annihilation.

Mechanisms in pp annihilation

We consider the annihilation mechanism in the antiproton momentum range 2.5 to 9.1 GeV/c. Techniques for identifying a “leading pion” are discussed. The annihilation is examined as a quasi two-body process, and the properties of the “leading pion” and the remaining multi-pion “cluster” are presented. A simple parametrization is found to reproduce satisfactorily several features of the data.

Is antiproton annihilation central or peripheral

Abstract A lower bound on the average impact parameter of p p annihilation is estimated from data on p p annihilation to pions at 4.6 and 9.1 GeV/ c . This bound is more central than for non-annihilation events. This result is in contrast to the simple interpretation of identifying the annihilation channels as responsible for the difference p p and pp scattering, since elastic scattering data show that this difference is particularly peripheral in impact parameters.

Single-pion production in antiproton-proton interactions

Single-pion production in pp interactions at 9.1 GeV/c is analysed and cross sections are given. The plab dependence of the isospin amplitudes is determined by a fit to the world data. The data are also compared with the predictions of a reggeized Deck model. The results and the NπN amplitudes are compared with the results at other energies and with the corresponding NπN amplitudes.