Production Of Baryon Resonances Research Articles

Analysis of the [formula omitted] reaction at 5.7 GeV/ c

From 63 760 four pronged events we have selected 10 960 events of the p pπ +π − final state. We have studied baryon resonances production and the associated production of Δ(1236) Δ(1236) isobars. We find (48.5 ± 2.6)% of Δ ++ Δ ++ and (4.5 ± 0.5)% of Δ 0 Δ 0 . Study of the various mass spectra shows that they are essentially described by the introduction of Δ ++ ( Δ ++ ) production. Introduction of the strong t dependence of the Δ ++ ( Δ ++ ) changes this description only slightly. A study of the interaction radius of the p π system reveals a best value of r = 1.6 ± 0.4 fm. Bumps observed in the p π + π − + c.c. system at 1450 and 1690 MeV when treated as resonances give rates of (4.0 ± 0.4)% and (4.5 ± 0.4)% respectively. We arrive at the conclusion that the reaction p p → p pπ +π − at 5.7 GeV/ c proceeds almost entirely via the production of baryon resonances.

ρ exchange and density matrices in baryon resonance production

ρ exchange and density matrices in baryon resonance production

K+p interactions near 3 GeV/c (II): Baryon resonance production

Abstract Baryon resonance production in quasi-two-body reactions has been studied for the channels K+p→K°pπ+, K+nπ+ and K+pπ° at beam momenta of 2.53, 2.76 and 3.20 GeV/c. The production cross sections, four-momentum transfer distributions and density matrix elements are given for the Δ(1236), N∗(1400), N∗(1500) and N∗(1680) states. The reaction K+p→K°Δ++(1236) is compared to the line reversed reaction K − n → K °Δ − and the charge-exchange SU(3) sum rule for pseudo-scalar meson plus Δ(1236) is tested.

Diffraction Dissociation and the Production of Baryon Resonances

A model incorporating virtual-meson diffraction scattering followed by a final-state resonant interaction of the meson with an emergent nucleon or isobar is proposed for the production of $I=\frac{1}{2}$ baryon resonances in the reaction $\mathrm{pp}\ensuremath{\rightarrow}p{{N}_{\frac{1}{2}}}^{*}$. Absolute predictions are compared with the experimental data relating to enhancements observed in missing-mass experiments. Agreement is favorable in the case of the ${P}_{11}(1470)$, but otherwise the many resonances predicted by phase-shift analyses complicate the issue and prevent a clear-cut test of the model. The proposed $\ensuremath{\Delta}P={(\ensuremath{-}1)}^{\ensuremath{\Delta}J}$ selection rule is discussed in relation to the large cross section predicted by the model for the "forbidden" ${S}_{11}(1150)$.

High-Energy Polarized-Photon Reactions

A general formalism is presented for the analysis of production and decay distributions of meson-baryon final states resulting from interactions of polarized photons and nucleons. Particular emphasis is given to high-energy reactions and Regge-pole exchange models. Circular polarization is shown to provide a test for the presence of two or more exchanges. Linear polarization parallel or perpendicular to the production plane allows the contributions of opposite $J$-parity exchanges to be separated. This formalism enables one to make use of data at all angles, rather than limit consideration to discrete points. Applications include the separation of diffractive and pion-exchange contributions to vector-meson production, and tests for non-pole-type exchanges in baryon-resonance production. Examination of pion photoproduction reveals that no simple test exists for the discrimination between pion conspiracy and evasion models.

Absorptive corrections to associated production of strange baryon and meson resonances in ?p scattering

Absorptive corrections are calculated for the reactionsπ + p→K *+∑+(K *+ Y 1 *+ ) mediated byK-exchange andπ +p→K+ Y 1 *+ withK *-exchange. The effect of the finite width of the resonances is included. Numerical results are given for 5 and 8 GeV/c.

Regge Poles in Resonance Production

The theory of Regge trajectory exchange is applied to the high-energy production of meson and baryon resonances. The helicity representation is used for the production amplitudes. The predictions are compared with experimental data on production of the ${N}^{*}(1238)$ nucleon resonance by pions and kaons, and also the production of the ${f}^{0}$ and $\ensuremath{\rho}$ mesons by pions. The energy dependence of the differential cross section is found to be consistent with the Regge-pole exchange model. Values for the $\ensuremath{\rho}$, ${A}_{2}$, and $\ensuremath{\pi}$ trajectories are determined. The $\ensuremath{\rho}$ and ${A}_{2}$ values are compared with those determined by analysis of elastic and charge-exchange scattering data. The $\ensuremath{\pi}$ trajectory values have not been determined in other reactions, but they are consistent with the known general properties of Regge trajectories. The spin density matrix elements are not strongly restricted by the theory, but the predictions that can be made are also consistent with experiment.

Asymptotic relations between cross sections for the baryon resonance production

The asymptotic equality of the cross sections of crossed inelastic processes with baryon resonance production is proved.

Baryon Resonance Production by Neutrinos and the Relativistic Generalizations ofSU(6)

An extension of our phenomenological study of baryon resonance production by neutrinos is carried out to include the relativistic generalizations of $\mathrm{SU}(6)$. The semileptonic weak-interaction Lagrangian invariant under the group $SL(6, c)$ is constructed for the 364-to-364 supermultiplet transitions. Two special cases are considered for this interaction Lagrangian: One invokes invariance under the larger group $M(12)$, while the other includes a simple $M(12)$ symmetry-breaking term. Detailed comparisons with the present experimental information on weak ${N}^{*}$ production and with the $\mathrm{SU}(6)$ theory are made for each of these relativistic symmetry schemes.

Baryon-resonance production by neutrinos

The production of the 3/2, 3/2 resonance by neutrinos incident on nucleons is considered in the framework of the Rarita-Schwinger formalism for spin-f particles. With the help of the conserved vector theory, and the Goldberger-Treiman relation, the value of certain coefficients is estimated. Wherever information is lacking, the static theory is used. The interaction determined in this way is then used to obtain total cross-sections. The result is that the total cross-section on complex nuclei as function of neutrino energy behaves similarly to, but is in absolute value larger than, the elastic process cross-section. Properties of the spin-3/2 density matrix under the combined assumptions of time-reversal invariance and Born approximation are derived and the general expression for the angular distribution of the decay pion in theN* rest frame is given.

Production of baryon resonances in the unitary symmetry model

Production of baryon resonances in the unitary symmetry model

Threshold mass numerologies and resonances in boson and baryon systems

Some of the more remarkable features between coincidences in mass thresholds for production of boson and baryon resonances and resonances in the baryon system are re-emphasized in connection with the cusp effect. The discussion is confined to three-body final states. The resonances are extremely narrow and consistent with zero width within experimental resolution. (N.W.R.)