arXiv subjects

E. Oset

Publications and source records attributed to E. Oset.

At least 451 records · Page 25Linked to original sources

arXiv2001

Study of polarization observables in double pion photoproduction on the proton

Using a model for two pion photoproduction on the proton previously tested in total cross sections and invariant mass distributions, we evaluate here polarization observables on which recent experiments are providing new information. We evaluate cross sections for spin 1/2 and 3/2, which are measured at Mainz and play an important role in tests of the GHD sum rule. We also evaluate the proton polarization asymmetry $Σ$ which is currently under investigation at GRAAL in Grenoble.

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arXiv2001

The role of Delta(1700) excitation and rho production in double pion photoproduction

Recent information on invariant mass distributions of the $γp\toπ^+π^0 n$ reaction, where previous theoretical models had shown deficiencies, have made more evident the need for new mechanisms, so far neglected or inaccurately included. We have updated a previous model to include new necessary mechanisms. We find that the production of the $ρ$ meson, and the $Δ(1700)$ excitation, through interference with the dominant terms, are important mechanisms that solve the puzzle of the $γp\toπ^+π^0 n$ reaction without spoiling the early agreement with the $γp\toπ^+π^- p$ and $γp\toπ^0π^0 p$ reactions.

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arXiv2001

Meson exchange in the weak decay of Lambda hypernuclei and the Gamma_n/Gamma_p ratio

We take an approach to the Lambda non-mesonic weak decay in nuclei based on the exchange of mesons. The one pion and one kaon exchange are considered, together with the exchange of two pions, either correlated, leading to an important scalar-isoscalar exchange (sigma-like exchange), or uncorrelated (box diagrams). Extra effects of omega exchange in the scalar-isoscalar channel are also considered. Constraints of chiral dynamics are used to generate these exchanges. A drastic reduction of the OPE results for the Gamma_n/Gamma_p ratio is obtained and the new results are compatible with all present experiments within errors. The absolute rates obtained for different nuclei are also in good agreement with experiment.

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arXiv2001

Test of phi renormalization in nuclei through phi photoproduction

We propose an experimental procedure to find out the medium modifications of the $ϕ$ meson. The reaction is inclusive $ϕ$ photoproduction in nuclei, looking for $K^+ K^-$ pairs from the $ϕ$ decay with total momentum smaller than 100-150 $MeV/c$, which are made possible at energies of present laboratories from center of mass $ϕ$ backward production and the help of Fermi motion. We have conducted a many body calculation of the mass distribution of the $ϕ$ adapted to the experimental set up of a recent JLAB experiment where the backwards $ϕ$ photoproduction has been measured. Using recent results for the in medium properties of the $ϕ$, we find that the width of the invariant mass distribution for photoproduction on medium to heavy nuclei is larger than the free $ϕ$ width by a factor of two or more.

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arXiv2001

Pion and Kaon Vector Form Factors

We develop a unitarity approach to consider the final state interaction corrections to the tree level graphs calculated from Chiral Perturbation Theory ($χPT$) allowing the inclusion of explicit resonance fields. The method is discussed considering the coupled channel pion and kaon vector form factors. These form factors are then matched with the one loop $χPT$ results. A very good description of experimental data is accomplished for the vector form factors and for the $ππ$ P-wave phase shifts up to $\sqrt{s}\lesssim 1.2$ GeV, beyond which multiparticle states play a non negligible role. In particular the low and resonance energy regions are discussed in detail and for the former a comparison with one and two loop $χPT$ is made showing a remarkable coincidence with the two loop $χPT$ results.

hep-ph↗

arXiv2001

Chiral unitary approach to the K^- deuteron scattering length

Starting from a recent model where the Kbar N amplitudes are evaluated from the chiral Lagrangians using a coupled channel unitary method, we evaluate here the scattering length for K^- deuteron scattering. We find that the double scattering contribution is very large compared to the impulse approximation and that the charge exchange contribution of this rescattering is as large as the sequential K^- scattering on the two nucleons. Higher order rescattering corrections are evaluated using coupled channels with K^- and Kbar^0 within the integral form of the fixed centre approximation to the Faddeev equations. The higher order corrections involving intermediate pions and hyperons are found negligible.

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arXiv2001

Chiral unitary theory: application to nuclear problems

In this talk we briefly describe some basic elements of chiral perturbation theory, $χPT$, and how the implementation of unitarity and other novel elements lead to a better expansion of the $T$ matrix for meson meson and meson baryon interactions. Applications are then done to the $ ππ$ interaction in nuclear matter in the scalar and vector channels, antikaons in nuclei and $K^-$ atoms, and how the $ϕ$ meson properties are changed in a nuclear medium.

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arXiv2001

Antikaons in nuclei and dense nuclear matter

We present recent progress on the properties of antikaons in nuclei and dense nuclear matter as obtained from two {\bar K}N interaction models: one based on the lowest-order meson-baryon chiral lagrangian and the other derived from a meson-exchange picture.

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arXiv2000

Chiral symmetry and meson exchange approach to hypernuclear decay

We take an approach to the $Λ$ nonmesonic weak decay in nuclei based on the exchange of mesons under the guidelines of chiral Lagrangians. The one pion and one kaon exchange are considered, together with the exchange of two pions, either correlated, leading to an important scalar-isoscalar exchange ($σ$-like exchange), or uncorrelated (box diagrams). A drastic reduction of the OPE results for the $Γ_n/Γ_p$ ratio is obtained and the new results are compatible with all present experiments within errors. The absolute rates obtained for different nuclei are also in fair agreement with experiment.

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arXiv2000

Pion and Kaon Vector Form Factors: a Chiral Unitary Approach

The pion and kaon coupled-channel vector form factors are described by making use of the resonance chiral Lagrangian results together with a suitable unitarization method in order to take care of the final state interactions. A very good reproduction of experimental data is accomplished for the vector form factors up to $\sqrt{s}\leq 1.2$ GeV and for the $ππ$ P-wave phase shifts up to $\sqrt{s}\leq 1.5$ GeV.

hep-ph↗

arXiv2000

$σ$ Exchange in the NN Interaction within the Chiral Unitary Approach

We study the nucleon-nucleon interaction in the isoscalar-scalar channel using t he chiral unitary approach. The $t$-matrix of the pion-pion scattering in this c hannel is summed up to all orders using the B-S equation. We find that the calcu lated results at long distances are close to those of the $σ$-exchange inte raction. In addition, there appears a shorter range repulsion in this channel.

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arXiv2000

The phi to pi+ pi- decay within a chiral unitary approach

Starting from the Chiral Perturbation Theory Lagrangian, but keeping different masses for the charged and neutral mesons, and using a previously developed non-perturbative unitary scheme that generates the lightest meson-meson resonances, we construct K Kbar to K Kbar and K Kbar to pi+ pi- in the vector channel. This allows us to obtain the kaon-loop contribution to the phi-rho mixing and study the phi to pi+pi- decay. The dominant contribution to this decay comes from the phi to gamma to pi+pi- process. However, there can be large interferences with the subdominant contributions coming from phi-rho and phi-omega mixing, or of these two contributions among themselves. As a consequence, a reliable measurement of phi to pi+pi- decay could be used to differentiate between some phi-omega mixing scenarios proposed in the literature.

hep-ph↗

arXiv2000

Two pion electroproduction

We have extended a model for the $γN\to ππN$ reaction to virtual photons and selected the diagrams which have a $Δ$ in the final state. The agreement found with the $γ_v p\toΔ^0π^+$ and $γ_v p\toΔ^{++}π^-$ reactions is good. The sensitivity of the results to $NΔ$ transition form factors is also studied. The present reaction, selecting a particular final state, is an extra test for models of the $γ_{v} N\to ππN$ amplitude.

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arXiv2000

The rho meson in a nuclear medium

In this work, propagation properties of the rho meson in symmetric nuclear matter are studied. We make use of a coupled channel unitary approach to meson-meson scattering, calculated from the lowest order Chiral Perturbation Theory lagrangian including explicit resonance fields. Low energy chiral constraints are considered by matching our expressions to those of one loop Ch.P.T. To account for the medium corrections, the rho couples to pion-pion and kaon-antikaon pairs which are properly renormalized in the nuclear medium.

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arXiv2000

Chiral Unitary Approach to the Kaon Nucleus Interaction and Kaonic Atoms

We review recent work on various topics related to the modification of kaon properties in nuclei. After a brief exposition of the kaon-nucleon and kaon-nucleus interaction, results from the application to kaonic atoms, renormalization of the f0 and a0 scalar resonances in nuclei and phi decay in the nucleus are shown.

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arXiv2000

Chiral Unitary Approach To The NNpi, NNeta Couplings For The N*(1535) Resonance

Using a chiral unitary model in which the negative parity nucleon resonance $N^\ast \equiv N^\ast(1535)$ is generated dynamically by means of the Bethe Salpeter equation with coupled meson baryon channels in the $S = 0$ sector, we have obtained the $π^0 N^\ast N^\ast$ and $ηN^\ast N^\ast$ couplings. The $π^0 N^\ast N^\ast$ coupling has smaller strength and the same sign as the $π^0 N N$ coupling. This rules out the mirror assignment of chiral symmetry where the ground state nucleon $N$ and the negative parity resonance $N^\ast$ are envisaged as chiral partners in the baryon sector.

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arXiv2000

Phi decay in nuclei

We have studied the decay of the ϕmeson in nuclear matter by taking into account the renormalization of the K and \bar{K} mesons in the medium. We separate the contribution of the total width into different reaction channels, K\bar{K} and KYh, the latter ones associated with the ϕN \to K^+ Y reactions. We find a total width at normal nuclear matter density of about 22 MeV, considerably larger than the free one.

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arXiv2000

Renormalization of the f0(980) and a0(980) scalar resonances in a nuclear medium

The meson meson interaction in the scalar sector in the presence of a nuclear medium is studied with particular attention to the change of the properties of the f0(980) and a0(980) resonances. By using a chiral unitary approach which generates the f0 and a0 resonances and reproduces their free properties, we find that the position of the resonances in the medium is barely changed but their widths are considerably broadened. New many body corrections generating from higher orders in the chiral Lagrangian plus the contribution from N*h excitations, not considered before in connection with the pion-pion interaction in the nuclear medium, are also investigated.

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