A study of the reactions π−p → K1X, K1Σ and K1Y11(1385) at 3.93 GeV/c

We have investigated the final states K¹⁰(890)Σ, $\text{K}{}^{10}\text{(890)Σ}{}^0$ and K¹⁰(890) Y₁¹⁰(1385) produced in π^?p interactions at 3.93 GeV/c. We present the differential cross sections and spin density matrix elements for the resonances as functions of momentum transfer, as well as the gL and Σ⁰ polarizations. The Σ⁰ polarization is found to be positive and maximal. An amplitude analysis is performed for the K¹ Λ and $\text{K}{}^1\text{Σ}{}^0$ reactions, and it is found that one natural parity transversity amplitude is dominant for the latter.     

A−2 production in π−p interactions at 3.9 GeV/c

The reaction π^?p → A^?₂p at 3.9 GeV/c incident momentum is studied using data corresponding to the ?^°π^?, ηπ^? and K^δ_sK^? decay modes of the A^?₂. Unnatural parity exchange is found to be important at this energy. The natural parity exchange component of the differential cross section exhibits structure at t′ ≈ GeV².     

A measurement of the branching ratios of the A2− meson produced in 3.9 GeV/cπ−ϱ interactions

We have measured the branching fractions of the A₂^? meson, produced in the reaction π^?p → pA₂^? at 3.9 GeV/c incident momentum. The rates for the ηπ and K$\text{K}$ modes relative to ?π are 0.211 ± 0.044 and 0.056 ± 0.014, respectively. The upper limit for the η′π mode is 0.056 at the 90% confidence level. We have also looked for an ωππ decay of the A₂^? and our data are consistent with a rate of 0.10 ± 0.05, relative to ?π.     

Study of π−π− scattering in π−n interactions at high energies

We have measured the inclusive cross section for the reaction π^?n→pX^?? at 21, 205 and 360 GeV/c in the kinematic region |t_np|<1.0 (GeV/c)². The differential cross sections can be described qualitatively by the reggeized one-pion-exchange amplitude at all momenta studied; however, there is evidence for the contribution of other amplitudes. The extracted π^?π^? total cross section for 4?s_ππ?340 GeV² is of the order of 10–12 mb. The average number of charged particles and dispersion of the charged particle multiplicity distributions for various s_ππ intervals are compatible with results observed in hadron-proton interactions.     

A study of π−π− scattering from π−p interactions at 3.93 GeV/c

A modified Chew-Low extrapolation procedure is applied to the reaction π^?p→Δ⁺⁺π^?π^? to extract the I = 2 ππ elastic cross sections from threshold to 1260 MeV. The predictions of the one-pion-exchange model are used to estimate the contributions from background processes of the type π^?p→Δ⁰?⁰. The moments of the π^?π^? angular distribution are also extrapolated to the pion pole and a phase shift analysis performed. The s-wave inelasticity is constrained using information on the inelastic cross section coming from six-body final states. The magnitude of the s-wave phase shift at the K⁰ mass is found to be 7.2⁰ ± 1.0⁰, increasing to 26.2⁰ ± 2.5⁰ at 1 GeV. d- and g-waves contribute above about 900 MeV, but the corresponding phase shifts are small compared with the s-wave. All three phase shifts have the same sign.     

Inclusive particle production in π− n interactions at high energies

Results on inclusive particle production in π^? n interactions at 21, 205 and 360 GeV/c are presented. The invariant cross sections in both neutron fragmentation and central regions are found to be equal within errors to the corresponding cross sections for π^? p collisions and exhibit the same energy dependence. A strong energy dependence of the invariant cross section ratios of negative and positive pions is observed. There is also an indication of transverse momentum dependence of these ratios. The η^? correlations in the neutron fragmentation region show little variation with energy and are in agreement with the predictions of the naive quark recombination scheme.     

ϱ0 and f production in π+p interactions

Inclusive ?⁰ and f(1270) production are analysed in π⁺p collisions at 8, 16 and 23 GeV/c. The ?⁰ cross section increases with energy such that the ?⁰/π^? ratio remains constant. Emphasis is laid on cross sections as a function of the transverse momentum and of the Feynman x variable. The ?⁰'s can be attributed to two sources: some ?⁰'s are centrally produced, but there is a pronounced forward peak. The distribution of leptons coming from ?⁰ decay is discussed.