arXiv subjects

A. Svarc

Publications and source records attributed to A. Svarc.

25 records · Page 2Linked to original sources

arXiv2004

The N(1710)P11 state is confirmed in the re-analysis of the pi N --> K Lambda production; it is a good candidate for a non-strange pentaquark

Re-analyzing the old pi N --> K Lambda data, the additional proof is given for the existence of the N(1710) P11 state, critically needed in light of reported observations of exotic Theta(1539) and Xi(1862) pentaquarks. An existing single-resonance model with S11, P11 and P13 Breit-Wiegner resonances in the s-channel has been applied. It has been shown that the standard set of resonant parameters fails to reproduce the shape of the differential cross section. The new resonance parameter determination has been performed keeping in mind the most recent knowledge about nucleon resonances. The extracted set of parameters has confirmed the need for the strong contribution of a N(1710) P11 resonance. The need for any significant contribution of the P13 resonance has been eliminated. To reproduce the total cross section at the same time with the linear dependence of the differential cross sections with the cos(theta) in the energy range 1650 MeV < W < 1800 MeV the P11 resonance can not but be quite narrow.

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arXiv2004

Nucleon resonances and processes involving strange particles

An existing single resonance model with S11, P11 and P13 Breit-Wiegner resonances in the s-channel has been re-applied to the old pi N --> K Lambda data. It has been shown that the standard set of resonant parameters fails to reproduce the shape of the differential cross section. The resonance parameter determination has been repeated retaining the most recent knowledge about the nucleon resonances. The extracted set of parameters has confirmed the need for the strong contribution of a P11(1710) resonance. The need for any significant contribution of the P13 resonance has been eliminated. Assuming that the Baker. et al data set\cite{Bak78} is a most reliable one, the P11 resonance can not but be quite narrow. It emerges as a good candidate for the non-strange counter partner of the established pentaquark anti-decuplet.

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arXiv2004

Presence of Extra P11 Resonances in Zagreb Analysis Since 1995

The partial wave T-matrices for the pi N, eta N and pi2 N channels have been obtained within the framework of the coupled channel model using the pi N elastic and pi N --> eta N data base as input. It has been shown that for the P11 partial wave an equally good representation of the experimental data (namely the T(pi N,pi N) and T(pi N,eta N) T-matrices) can be obtained using either three, or four poles for the Green function propagator. However, the three Green function pole solution is not acceptable due to the structure of the extracted resonances. The two out of four P11 resonances, those lying in the energy range 1700 MeV < MR < 1800 MeV, are poorly determined, but they seem to be strongly inelastic. The inclusion of other inelastic channels is needed to determine masses and widths of missing resonances with greater precision.

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arXiv2004

The detailed mechanism of the eta production in pp scattering up to the Tlab = 4.5 GeV

Contrary to very early beliefs, the experimental cross section data for the eta production in proton-proton scattering are well described if pi and only eta meson exchange diagrams are used to calculate the Born term. The inclusion of initial and final state interactions is done in the factorization approximation by using the inverse square of the Jost function. The two body Jost functions are obtained from the S matrices in the low energy effective range approximation. The danger of double counting in the p-eta final state interaction is discussed. It is shown that higher partial waves in meson-nucleon amplitudes do not contribute significantly bellow excess energy of Q=100 MeV. Known difficulties of reducing the multi resonance model to a single resonance one are illustrated.

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arXiv2001

The importance of the nucleon-nucleon correlations for the eta alpha S-wave scattering length, and the pi-eta mixing angle in the low-energy eta alpha scattering length model

Using the new set of dd --> eta alpha near threshold experimental data, the estimate of the importance of the nucleon-nucleon correlations for the eta alpha S-wave scattering length in the multiple scattering theory is obtained using the low-energy scattering length model. The contribution turns out to be much bigger then previously believed. The pi-eta mixing angle is extracted using the experimental data on the dd --> eta alpha and dd --> pi alpha processes. The model is dominated by the subthreshold extrapolation recipe for the eta alpha scattering amplitudes. When the recipe is chosen the model is completely insensitive to the eta alpha parameters for the subthreshold value of the eta cm momentum of p_{eta}^2 = -(0.46)^2 fm^{-2}. Provided that the subthreshold extrapolation recipe is correct, a good estimate of the pi-eta mixing angle is obtained, if the experimental cross sections for the dd --> pi alpha reaction at the corresponding deuteron input energy are taken from the literature.

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arXiv1999

Evidence for the fourth P11 resonance predicted by the constituent quark model

It is pointed out that the third of five low-lying P11 states predicted by a constituent quark model can be identified with the third of four states in a solution from a three-channel analysis by the Zagreb group. This is one of the so-called ``missing'' resonances, predicted at 1880 MeV. The fit of the Zagreb group to the pi N -> eta N data is the crucial element in finding this fourth resonance in the P11 partial wave.

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arXiv1996

Near threshold eta production in proton-proton collisions

The total cross section for the near threshold eta production in proton-proton collisions has been investigated with the assumption that the production mechanism is due to the emission of a meson x (pi, eta, sigma) from one of the nucleons followed by a x N --> eta N transition on the second one. The x N --> eta N amplitudes are generated from the unitary multi-channel multi-resonance model which has recently been constructed in analyzing the pi N scattering and pi N --> eta N reaction. The initial and final pp distortions are calculated from a coupled-channel pi-NN model which describes the NN scattering data up to about 2 GeV. With the x-NN vertex functions taken from the Bonn potential, the predicted total cross sections of threshold pp --> eta pp reaction are in good agreement with the data. In contrast to previous works, we find that the eta-exchange plays an important role. The effect of the two-pion exchange, simulated by sigma- exchange, is found to be significant but not as dominant as the vector meson-exchange introduced in previous works.

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