We report a study of 20 exclusive reactions measured at the AGS at 5.9 GeV/c incident momentum, 90° center of mass. This experiment confirms the strong quark flow dependence of two-body hadron-hadron scattering at large angle. At 9.9 GeV/c an upper limit had been set for the ratio of cross sections for (p¯p→p¯p)(pp→pp) at 90° c.m., with the ratio less than 4%. The present experiment was performed at lower energy to gain sensitivity, but was still within the fixed angle scaling region. A ratio R(p¯ppp)≈140 was measured at 5.9 GeV/c, 90° c.m. in comparison to a ratio near 1.7 for small angle scattering. In addition, many other reactions were measured, often for the first time at 90° c.m. in the scaling region, using beams of π±, K±, p, and p¯ on a hydrogen target. There are similar large differences in cross sections for other reactions: R(K−p→π+Σ−K−p→π−Σ+)≈112, for example. The relative magnitudes of the different cross sections are consistent with the dominance of quark interchange in these 90° reactions, and indicate that pure gluon exchange and quark-antiquark annihilation diagrams are much less important. The angular dependence of several elastic cross sections and the energy dependence at a fixed angle of many of the reactions are also presented.
Cross sections at 90 degrees in the centre-of-mass.
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A high-statistics experiment on the reaction π − p→ π + π − π 0 n at 8.06 GeV/ c has been performed using a spectrometer detecting both charged particles and gamma rays. A partial-wave analysis based on the isobar model has been carried out for π + π − π 0 data in the mass range between 0.86 and 1.50 GeV for four t ′ regions: 0.0–0.1, 0.1–0.25, 0.25–0.45 and 0.45–0.95 (GeV/ c 2 ). Two axial-vector resonances, a 1 (1260) and h 1 (1170), were observed in the analysis. The masses and widths of a 1 and h 1 were determined to be M (a 1 = 1121 ± 8 MeV, Λ (a 1 = 239± 11 MeV, M (h 1 = 1168±4 MeV and Λ (h 1 = 345±6 MeV, respectively, by fitting the Breit-Wigner formula to the partial wave amplitude. A fit including the Deck type background was also tried in each t ′ region. The results showed a small effect on these resonance parameters and were consistent with those obtained by the simple Breit-Wigner fitting.
Production cross section of A2(1320) from the 12+ rhoD1+ partial wave.
Production cross section of H1(1190) from the 01+ rhoS0+ partial wave.
Production cross section of A1(1270) from the 11+ rhoS1+ partial wave.
High statistics data of the ηππ system in π − p → ηπ + π − n were obtained. A partial wave analysis was performed in the mass region between 1.37 and 1.85 GeV. Resonant structures were observed in the IJ PC = 11 −− wave around 1.6 GeV and in 13 −− around 1.7 GeV. The structure in 11 −− was fitted with a single Breit-Wigner and also fitted with two Breit-Wigner's. The result suggests the possible existence of two vector resonances around 1.6 GeV. The structure in 13 −− is considered to be the π 3 (1690).
Result of single Breit Wigner fit around 1.6 GeV. Called here $M(1635).
Results of double Breit Wigner fit around 1.6 GeV. $M(1446) and $M(1701).
Result of Breit Wigner fit around 1.7 GeV.
The analysis of exclusive neutral strange particle production in the reactions π − p → K° Λ + K° Σ ° and p p → Λ Λ + Λ Σ° + c.c. at 3.15, 4.95, 7.9 and 12 GeV/ c yielded the differential cross section distributions up to about 90° c.m.s. scattering angle and the Λ-particle polarization at large transverse momentum. Applying a fit to d σ /d t ∞ s − n resulted in n = 8.6 ± 0.9 for the K° Λ + K° Σ° final state which is compatible with the quark counting rule n = 8 for meson-baryon reactions. The average Λ polarization around t = −1.6 (GeV/ c ) 2 was P Λ = 0.79 ± 0.17 at 3.15 GeV/ c beam energy.
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Axis error includes +- 0.0/0.0 contribution (?////NOT GIVEN).
Axis error includes +- 0.0/0.0 contribution (?////NOT GIVEN).
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The results of the study of the π + p→K + ∑ + (1) and π + p→K + ∑ + (1385) (2) reactions at 12 GeV/ c are presented. The differential cross sections d σ /d t in| t min |<| t |<0.8 (GeV/ c ) 2 momentum transfer range are measured. The ∑ + polarisation for | t |<0.5 (GeV/ c ) 2 for reaction (1) is defined. Binary reactions (1) and (2) were selected by analyzing the missing mass spectra for the forward emitted fast K + meson. The total cross sections in the studied momentum transfer range are 20.2±2.4 μ b and 7.3±1.1 μ b for the reactions (1) and (2) respectively. The experimental results are compared with the predictions of the Regge models which take into account rescattering and secondary singularities.
SYSTEMATIC ERRORS INCLUDED.
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Results of a high-statistics study of elastic scattering and meson resonances produced by π−p interactions at 8 GeV/c are presented. Large statistics and small systematic errors permit examination of the complete kinematic region. Total differential cross sections are given for ρ0,−, f0, g0,−, Δ±, Δ0, and N* resonances. Spin-density matrix elements and Legendre-polynomial moments are given for ρ, f, and Δ resonances. The results for ρ0 and f0 resonances are compared with the predictions of a Regge-pole-exchange model. Properties of the above resonances are compared and discussed. In particular, we present evidence that the ρ0 and f0 production mechanisms are similar. The similarity of the g0 t distribution to that of the ρ0 and f0 suggests a common production mechanism for all three resonances.
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SLOPE REFERS TO EXPONENTIAL FIT IN U.
Results are presented for the quasi two-body hypercharge exchange reactions of the type 0−1/2+→2+1/2+:$$\begin{gathered}
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Exotic exchange processes observed in K − p and π − p scattering in the neighbourhoood of 4 GeV/ c are analysed in terms of standard models. Some new data on π − p induced processes are presented and used in the analysis. Regge-Regge cut predictions are found to be smaller than the data up to these energies. Baryonium exchange models are shown to be indistindistinguishable from Regge cut models as regards their phenomenological predictions. The double scattering quark model of Białas and Zalewski is compatible with data on the exotic exchange production of Σ and Y ∗ (1385), but fails for Ξ and Ξ ∗ (1530) production. Modifications of this model are discussed.
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FORWARD (SMALL -T) CROSS SECTIONS. THE K- P CROSS SECTIONS ARE COMPUTED FROM THE ACNO DATA AT 4.2 GEV/C, M. MAZZUCATO ET AL., NP B178, 1 (1981).
BACKWARD (SMALL -U) CROSS SECTIONS.
The reactionsπ−p→K0(890) Λ,K0(890)Σ0 andK0(890)Σ0 are studied at an incident momentum of 3.95 GeV/c using data from a high statistics bubble chamber experiment corresponding to ∼90 events/μb. The differential cross sections, density matrix elements of the vector meson and hyperon polarizations are presented. A transversity amplitude analysis is performed for each of the reactions. The results are compared with those obtained for the SU(3) related processesK−p→ϕΔ, ϕΣ0, ϕΣ0(1385) andϱ−Σ+(1385) and with predictions of the additive quark model and SU(6) sum rules.
BREIT-WIGNER FIT WITH BACKGROUND POLYNOMIAL.
BACKWARD CROSS SECTION.
TOTAL CROSS SECTION USING SLICING TECHNIQUE. FORWARD (-TP < 1.2 GEV**2) CROSS SECTION IS 25 +- 2 MUB: DOUBLE MASS CUT GIVES 20 +- 7 PCT BACKGROUND CONTAMINATION.
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