Isobaric States Research Articles

The width of isobaric states observed in (p, n) reactions

The width of isobaric states observed in (p, n) reactions

Hyperons with and without Doublet Symmetry

The object of this study is a system containing a baryon with the properties of the $\ensuremath{\Lambda}\ensuremath{-}\ensuremath{\Sigma}$ quartet, in strong interaction with mesons which may be bound to form various isobar states. The model involves two independent coupling constants $g$ and ${g}^{\ensuremath{'}}$. It will be shown that the case $g={g}^{\ensuremath{'}}$ which corresponds to doublet (or global) symmetry is singular in that it is strongly affected by a certain quantum-mechanical resonance.

Pion Production in Pion-Nucleon Collisions and the Pion-Pion Interaction

Momentum distributions of the pions of all charge states produced in the interaction of 960-Mev pi /sup -/ mesons with protons are calculated assuming a primary pi pi interaction followed by a pi -N interaction with excitation of the (3,3) isobar state of the nucleon. Predicted spectra are in reasonable agreement with experimental data when the pi - pi resonance energy is assumed to be about 700 Mev. (auth)

Persistence of Isobaric Correspondence Between Nuclear States in Mass Regions Where Isotopic Spin is not a Good Quantum Number

An attempt is made to give the theoretical basis for the incorrectness of the assumption that the extent to which states of two isobaric nuclei are similar is determined by the degree of isotopic spin purity in the nuclei. It is shown that correspondence between isobaric nuclear states can persist well beyond the mass region where isotopic spin is a good quantum number. (L.N.N.)

Proton-Antiproton Collision and Isobaric States

Branching ratios for the reaction p + p yields K + K- + pi + pi are examined to determine modifications resuiting when either substate plays the more important role. Discussions as to the relative importance of the substates are presented. The isobaric states in pi -K, pi -N, pi -A, and pi - SIGMA systems are considered.

Baryon mass differences and isobar states

Two of three different fundamental vector fields were postulated theoretically for isospin and baryon number conservation. The third, necessary for the complete gage invariant approach to strong interactions, is presented; experimental data are used in conjunction with theoretical arguments. Thus, possible connections of different experimental aspects reduce arbitrariness and the number of different assumptions necessary to explain the phenomenology of the strong interactions.

On the Strong Interactions of the Strange Particles

The theory appropriate to the definition and application of the reaction matrix is reviewed. The analysis of the low-energy K--proton data is reviewed in terms of this formalism, and the K -nucleon virtual bound state interpretation of the pi - LAMBDA resonance is compared with experimental data. The use of this formalism and its relationship with the reaction-matrix formalism are discussed, with special reference to the description of resonant states. The present evidence bearing on the validity of the global symmetry hypothesis is reviewed, and the interpretations of the pi - LAMBDA resonance as an analog of the (3,3) isobar state in the pi -N system are discussed and compared with data. (L.T.W.)

A separable potential for the two-nucleon ( T = 1) interaction

A separable potential in the isobaric state T = 1 is proposed on the basis of p—p scattering data up to about 100 MeV. The triplet part of this potential is taken to be purely of the spin-orbit type, with a range about half of that of the singlet potential. Potentials in states l ≧ 3 are neglected. It is found that such a potential can rather satisfactorily explain the angular shape of the unpolarized cross section as well as the magnitude of the polarization in scattering up to 100 MeV.

An Isobaric StateK*inK-π System and $p+\bar{p}\to K+\bar{K}+\pi+\pi$ Process

The isobaric state K* can be investigated bv obtaining experimental data for energy spectra of nucleons in the reaction K + N-- K + pi + N. The reaction p +p-- K + K + pi + pi would be measured. It is assumed that the reaction takes place mainly through the process p + p-- K* + K* -K + K + pi + pi . Branching ratios are estimated and tabulated. (L.N.N.)

Analysis ofK-Meson Production byp¯Annihilation

$K$-meson production by $\overline{p}$ annihilation has been investigated using an isobar model. A comparison of the predictions of this model with the experimental data excludes the assumption of an isobar state of ($\ensuremath{\pi}\ensuremath{\pi}$) having a mass greater than three pion masses.

The S Wave Pion-Pion Interaction

The pion-pion interaction has been studied with an explicit appeal to the standard quantum field theory. Lowest order perturbation theory calculations indicate that the usual renormalization procedure may imply an indefinite quantization metric. An alternative procedure, using a regulator cut-off near the nucleon mass, is therefore adopted, and on this basis the following conclusions are drawn. The short range pion-pion interaction is found to be highly repulsive in states of isobaric spin I=0 and 2, giving a hard-core scattering The short range repulsion vanishes in the states with I=1. The long range interaction is attractive in the even isobaric spin states but is very small. An `effective' pion-pion coupling constant is obtained in terms of a0 and a2, the hard-core radii in states of isobaric spin I=0 and 2, and μ, the meson rest mass: λeff (16π/5)a0μ (16π/5)a2μ

Application of ρ-Meson Theory to 5 Bev π--pData

The angular distribution of protons from pi- -p inelastic collisions at 5 Bev suggests a sharp tendency to forward scattering, and this fact is favorable for the existence of some isobaric states. Using rho-meson or (1,1) nucleoneum, a Feynman diagram was calculated and applied to the 5 Bev data. (N.W.R.)

Central and peripheric interactions of 7.3 GeV negative pions in emulsions

534 interactions of 7.3 GeV negative pions in an emulsion stack have been studied. Average multiplicities of heavy prongs and shower particles were obtained. Individual Lorentz factorsγc were computed for 395 showers withns⩾3. A detailed study is made of theγc-spectrum of events from light nuclei. This spectrum appears structured into head-on collisions with one or two nucleons and peripheric collisions involving one or two pions in the struck nucleon’s meson cloud. Pion-pion collisions show a marked « two-centre » structure, attributed tentatively to the formation and isotropic two pion decay of pionic resonant (isobaric) states of mass ∼3 μ. The e−-e+-pair spectrum from π0-decay has been measured and yields an average inelasticity of ∼ 75% in π−-nucleus collisions.

Multiple Meson Production by Photons in Hydrogen

The analysis of 235 events of double meson production by photons with energy up to 1.1 Bev (reaction $\ensuremath{\gamma}+p\ensuremath{\rightarrow}p+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$) observed in a ${\mathrm{H}}_{2}$ diffusion cloud chamber has produced the following results. The cross section rises rapidly at about 500 Mev to a value of approximately 70 \ensuremath{\mu}b. The angular, momentum, and $Q$ distributions of the reaction products cannot be satisfactorily accounted for either by a pure statistical model, or by a pure isobaric state model, or by a model assuming interaction of the incoming photon with the meson cloud of the proton, leading to $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ interaction. The observation of 14 cases of the reactions $\ensuremath{\gamma}+p\ensuremath{\rightarrow}p+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{0}$ and $\ensuremath{\gamma}+p\ensuremath{\rightarrow}n+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$ suggests that the combined cross section for these reactions is about 10 \ensuremath{\mu}b between 700 and 1000 Mev.

Mesons and the struture of nucleons: Part III. Pion-nucleon scattering

The “atomic” model of the physical nucleons has been used in a direct computation of the scattering of free pions by nucleons. The computation is analogous to the computation of the scattering of electrons by hydrogen atoms. Neglecting any pion-pion interaction, p-wave scattering phase shifts are computed, in the Born approximation and also by an improved technique, for various assumptions concerning the interaction between a pion and the nucleon “core”. The model is shown to be capable of reproducing the resonant scattering in the (3,3) isobar state, while predicting much smaller phase shifts for the other states. Our results differ from the Chew-Low theory, in the Born approximation, only in that we predict a small, positive phase-shift for scattering in the (1,1) state; the experiments appear to favor our prediction. We conclude that the same pion-nucleon interaction, which accounts for the properties of the ground (physical) nucleon state, leads to the observed low-energy pion-nucleon scattering.

Pion-pion interaction and multiple pion production in nucleon-antinucleon annihilation process

The multiple pion production in antinucleon-nucleon annihilation processes is investigated by means of the statistical theory with the strong pion-pion interaction. The characteristics of the isobar state of two pions are determined from the observed momentum distribution of a nucleon in the reaction π-+p →N + 2π at 1 GeV or from the theories of Takeda, Dyson and Miyazawa. The mean number of produced pions is 3÷4 and rather less than that given by experiment.

Possible New Isobaric State of the Proton

Possible New Isobaric State of the Proton

Pion Production in Pion-Nucleon Collisions

The single production of pions occurring in pion-nucleon collisions at incident pion energies below \ensuremath{\sim}1.5 Bev has been considered in terms of the inelastic excitation of the nucleon to the isobaric state with isotopic spin and $\mathrm{angular}\mathrm{momentum}=\frac{3}{2}$, previously identified with the resonant state in the low-energy pion-nucleon scattering. An associated separate recoil pion accompanies the isobar, and conserves energy and momentum. The isobar subsequently decays into a nucleon and a pion. Expressions have been obtained for the branching ratios between the different reactions, ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{+}+n$, and ${\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{0}+p$, and for the separate energy spectra of the ${\ensuremath{\pi}}^{+}$, ${\ensuremath{\pi}}^{0}$, and ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons. The momentum distributions of the pions and recoil nucleons have been calculated at incident pion energies of 0.93 Bev and 1.37 Bev, and are generally in reasonable agreement with the experimental data available at these energies.

Low energy $$\bar K$$ -nucleon scattering-nucleon scattering

Thes-wave low energy scattering of\(\bar K\)-mesons on nucleons is studied using a similar method as that applied, in a previous work, for the K-N interaction. Disregarding virtual barion-antibarion pair effects, K virtual state contributions and barion recoil, the integral equations for the two isobaric spin state amplitudes are exactly solved, and analytical expressions for the phase shifts are given. Results are rather independent on the cut-off energy and indicate repulsive potential for both isobaric spin eigenstates. Numerical results are presented for the values of the coupling constants suggested in the previous work.

Isobar Model for Meson Production in Proton-Proton Collisions

A model is considered for single- and double-pion production in which the production takes place via an intermediate state wherein either one or both of the initial nucleons is excited to the isobaric state of $J=I=\frac{3}{2}$. The treatment is phenomenological and comparison is made with recent experiments in the 0.5- to 1.5-Bev range. Two striking features of the experiments, the strong preference for the emission of mesons with kinetic energies of 50 to 150 Mev, and the rapid increase in the two-meson processes at bombarding energies above 1 Bev, are exhibited by the calculation.