R. Carlsson

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.

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.

Study of Interference Effects of Identical Pions in 9.1 GeV/c bar pp-Interactions

We present a study of the Bose-Einstein interference effect for pions of equal charge and similar momentum vectors in inclusive antiproton-proton reactions at 9.1 GeV/c. The results are used to provide an estimate of the space-time dimensions of the region emitting the pions. We obtain an average radius R = 1.3 ± 0.1 fm and a time of emission cτ = 0.9 ± 0.2 fm. The parameter λ, a measure of the fraction of interfering like-charge pions, is found to be λ = 0.8 ± 0.1. No large deviation from a spherical shape of the pion source is observed. We emphasize the importance of establishing a non-interfering background.

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.

Search for charmed matter in 9.1 GeV/c antiproton-proton reactions

A search for heavy mesons decaying to p p ¯ , p p ¯ π ..., K K ¯ , K K ¯ π ... and Kπ, Kππ… in 9 GeV/c antiproton-proton reactions has been made. Based on a sample of 9514 events with p p ¯ and 139 events with K K ¯ , no evidence for masses in the region 1–4 GeV/c2 was found. The inclusive strange particle cross sections were estimated to be σλ0) = 0.65 ± 0.05 mb and σKS0 = 1.20 ± 0.07 mb.

A test of factorisation predictions for the fragmentation processes pp→π± at p momenta of 9.1 and 4.6 GeV/c

Abstract Relations have been derived between the invariant cross sections for various inclusive processes by assuming factorisation of the leading (pomeron) and non-leading (meson) trajectories. In this paper predictions for the invariant cross sections f( p p →π ± )(2E ∗ /π√s) d 2 σ/ d x d p 2 ⊥ 2 have been tested using data from p p interactions at 4.6 and 9.1 GeV/ c . A large discrepancy between experiment and theory is apparent for the π − data: in the π + case the discrepancy is less marked but still present.

Study of the reaction p̄p → p̄ωp at 9.1 GeV/c

Abstract The reaction pp → ppπ + π − π 0 has been studied at 9.1 GeV/ c . The cross section is 2.04 ± 0.04 mb based on 3062 events. The cross section for pp→ pωp is 0.17 ± 0.02mb. The p lab dependence on this cross section is p lab −0.9 ± 0.2 . This rules out a double Regge pole exchange model with a pomeron trajectory.