0000000000177496
AUTHOR
J.c. Nacher
Photoproduction of neutral pion pairs from the proton
Double neutral pion photoproduction from the proton has been measured at MAMI for photon energies between threshold and 820 MeV. The reaction was identified by an invariant mass and missing mass analysis. From threshold up to 370 MeV the total cross-section does not exceed 30 nb. For higher energies it shows a smooth rise until it reaches a maximum of about 10 μb at Eγ = 740 MeV. Dalitz plots of m2(π0π0) versusm2(p,π0) for seven bins of incident photon energy have been analysed. For Eγ > 610 MeV, a strong contribution of a sequential decay is observed with the Δ(1232)-resonance as intermediate state. A comparison to model calculations shows that these sequential decays presumably originate …
Magnetic moments of theΛ(1405)andΛ(1670)resonances
By using techniques of unitarized chiral perturbation theory, where the $\ensuremath{\Lambda}(1405)$ and $\ensuremath{\Lambda}(1670)$ resonances are dynamically generated, we evaluate the magnetic moments of these resonances and their transition magnetic moment. The results obtained here differ appreciably from those obtained with existing quark models. The width for the $\ensuremath{\Lambda}(1670)\ensuremath{\rightarrow}\ensuremath{\Lambda}(1405)\ensuremath{\gamma}$ transition is also evaluated, leading to a branching ratio of the order of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}.$
Recent progress on the chiral unitary approach to meson meson and meson baryon interactions
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.
The role of Delta(1700) excitation and rho production in double pion photoproduction
Recent information on invariant mass distributions of the $\gamma p\to\pi^+\pi^0 n$ 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 $\rho$ meson, and the $\Delta(1700)$ excitation, through interference with the dominant terms, are important mechanisms that solve the puzzle of the $\gamma p\to\pi^+\pi^0 n$ reaction without spoiling the early agreement with the $\gamma p\to\pi^+\pi^- p$ and $\gamma p\to\pi^0\pi^0 p$ reactions.
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 $\Sigma$ which is currently under investigation at GRAAL in Grenoble.
Photoproduction of the Lambda(1405) on the proton and nuclei
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 irrelev…
Photoproduction of meson and baryon resonances in a chiral unitary approach
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.
SU(3) Chiral approach to meson and baryon dynamics
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\to\Lambda(1405)\gamma reaction and the N^\ast (1535)N^\ast(1535)\pi and \eta couplings.