arXiv subjects
Publications and source records attributed to J. C. Nacher.
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.
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.
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. With this model we have evaluated cross sections for the virtual photon cross section as a function of $Q^2$ for different energies. 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. The experimental measurement of the different isospin channels for this reaction are encouraged as a means to unravel the dynamics of the two pions photoproduction processes.
By means of a coupled channel non-perturbative unitary approach, it is possible to extend the strong constrains of Chiral Perturbation Theory to higher energies. In particular, it is possible to reproduce the lowest lying resonances in meson-meson scattering up to 1.2 GeV using the parameters of the O(p^2) and O(p^4) Chiral Lagrangian. The meson baryon sector can also be tackled along similar lines. We report on an update of these results showing some examples of photon induced reactions where the techniques have been recently applied.
We report on recent progress on the chiral unitary approach, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV and meson baryon interaction up to the first baryonic resonances. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented, concretely the K^- p\toΛ(1405)γreaction and the N^\ast (1535)N^\ast(1535)πand ηcouplings.
We report on recent progress on the chiral unitary approach, analogous to the effective range expansion in Quantum Mechanics, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented, in which two hadrons, either two mesons or a meson and a baryon, in a resonant state are produced in photoproduction processes.
We have carried a theoretical study of the K^- p\to M B γreaction with M B = K^-p, \bar{K}^0 n, π^- Σ^+, π^+ Σ^-, π^0 Σ^0, π^0 Λ, for K^- lab. momenta between 200 and 500 MeV/c, using a chiral unitary approach for the strong K^-p interaction with its coupled channels. The Λ(1405) resonance, which is generated dynamically in this approach, shows up clearly in the dσ/dM_I spectrum, providing new tests for chiral symmetry and the unitary approach, as well as information regarding the nature of the resonance. The photon detection alone, summing all channels, is shown to reproduce quite accurately the strength and shape of the Λ(1405) resonance. Analogous reactions in nuclei can provide much information on the properties of this resonance in a nuclear medium.
We report on recent progress on the chiral unitary approach, analogous to the effective range expansion in Quantum Mechanics, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented. Results for the extension of these ideas to the meson baryon sector are discussed, together with applications to kaons in a nuclear medium and $K^-$ atoms.
We study the gamma p ---> K^+ Lambda(1405) reaction at energies close to threshold using a chiral unitary model where the resonance is generated dynamically from K^-p interaction with other channels constructed from the octets of baryons and mesons. Predictions are made for cross sections into several channels and it is shown that the detection of the K^+ is sufficient to determine the shape and strength of the Lambda(1405) resonance. The determination of the resonance properties in nuclei requires instead the detection of the resonance decay channels. Pauli blocking effects on the resonance, which have been shown to be very important for the resonance at rest in the nucleus, are irrelevant here where the resonance is produced with a large momentum. The nuclear modifications here would thus offer information on the resonance and K^- nucleus dynamics complementary to the one offered so far by K^- atoms.
We report on reactions producing two pions induced by real and virtual photons or nucleons. The role of different resonances in these reactions is emphasized. Novel results on coherent two pion photoproduction in nuclei are also reported.