arXiv subjects

M. J. Vicente Vacas

Publications and source records attributed to M. J. Vicente Vacas.

At least 109 records · Page 6Linked to original sources

arXiv2005

Dynamical generation of $J^P=3/2-$ resonances and the $Λ(1520)$ resonance

The lowest order chiral Lagrangian is used to study s-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons. The coupled channel Bethe Salpeter equation is used to obtain dynamically generated $\tfrac{3}{2}^-$ resonances in the partial wave amplitudes which provide a reasonable description to a number of 3 and 4-star resonances like $Δ(1700)$, $Λ(1520)$, $Σ(1670)$, $Σ(1940)$, $Ξ(1820)$, $Ω(2250)$ etc. The phenomenological introduction of d-wave channels in the coupled channel scheme along with the existing s-wave channels is shown to provide a much improved description of the $Λ(1520)$ resonance. The prediction of the absolute strength of the cross section in the reactions $K^-p\toΛπ^0π^0$ and $K^-p\toΛπ^+π^-$ provided by this scheme shows a good agreement with existing data.

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arXiv2005

Chiral coupled channel dynamics of the Lambda(1520) and the K-P -> pi0 pi0 Lambda reaction

We study the $Λ(1520)D_{03}$ in a chiral coupled channel approach. This resonance appears as dynamically generated from the interaction of the decuplet of baryons and the octet of mesons in s-wave, and its treatment is improved here with the phenomenological inclusion of the $\bar{K} N$ and $πΣ$ channels in d-wave. Since the most important building block in the $Λ(1520)$ is the $π\Sgs(1385)P_{13}$ channel, we study the $K^- p \to π\Sgs(1385) (π^0 Λ)$ reaction in the region of the $Λ(1520)$ and above, and compare the results with recent experimental data. With the coupling of the $Λ(1520)$ to the $π\Sgs$ channel predicted by the theory we find a cross section in good agreement with the data and there is as well agreement for the invariant mass distributions which show a neat peak for the $\Sgs(1385)$ in the $(π^0 Λ)$ spectrum. Predictions are made of a strong $Λ(1520)$ resonant peak of the cross section, as a function of the $K^-$ momentum, in the region below the measured data which, if confirmed experimentally, would give a stronger support to the idea of the $Λ(1520)$ as a dynamically generated resonance.

hep-ph↗

arXiv2005

Chiral dynamics of baryon resonances and hadrons in a nuclear medium

In these lectures I make an introduction to chiral unitary theory applied to the meson baryon interaction and show how several well known resonances are dynamically generated, and others are predicted. Two very recent experiments are analyzed, one of them showing the existence of two $Λ(1405)$ states and the other one providing support for the $Λ(1520)$ resonance as a quasibound state of $Σ(1385) π$. The use of chiral Lagrangians to account for the hadronic interaction at the elementary level introduces a new approach to deal with the modification of meson and baryon properties in a nuclear medium. Examples of it for $\bar{K}$, $η$ and $ϕ$ modification in the nuclear medium are presented.

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arXiv2005

Two-meson cloud contribution to the baryon antidecuplet binding

We study the two-meson virtual cloud contribution to the self-energy of the SU(3) antidecuplet, to which the Theta+ pentaquark is assumed to belong. This is motivated by the large branching ratio of the N(1710) decay into two pions and one nucleon. We derive effective Lagrangians that describe the N(1710) decay into N-pi-pi with two pions in s or p wave. We obtain increased binding for all members of the antidecuplet and a contribution to the mass splitting between states with different strangeness which is at least 20 % of the empirical one. We also provide predictions for three-body decays of the pentaquark antidecuplet.

hep-ph↗

arXiv2005

Study of a possible S=+1 dynamically generated baryonic resonance

Starting from the lowest order chiral Lagrangian for the interaction of the baryon decuplet with the octet of pseudoscalar mesons we find an attractive interaction in the $ΔK$ channel with L=0 and I=1, while the interaction is repulsive for I=2. The attractive interaction leads to a pole in the second Riemann sheet of the complex plane and manifests itself in a large strength of the $ΔK$ scattering amplitude close to the $ΔK$ threshold, which is not the case for I=2. However, we also make a study of uncertainties in the model and conclude that the existence of this pole depends sensitively upon the input used and can disappear within reasonable variations of the input parameters. We take advantage to study the stability of the other poles obtained for the ${3/2}^-$ dynamically generated resonances of the model and conclude that they are stable and not contingent to reasonable changes in the input of the theory.

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arXiv2005

Production of $Θ^+$ Hypernuclei with the $(K^+,π^+)$ reaction

We present results on the production of bound states of $Θ^+$ in nuclei using the $(K^+,π^+)$ reaction. By taking into account the states obtained within a wide range of strength of the $Θ^+$ nucleus optical potential, plus the possibility to replace different nucleons of the nucleus, we obtain an excitation spectra with clearly differentiated peaks. The magnitude of the calculated cross sections is well within reachable range.

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arXiv2005

Evaluation of the $ππ$ scattering amplitude in the $σ$-channel at finite density

The $ππ$ scattering amplitude in the $σ$-channel is studied at finite baryonic density in the framework of a chiral unitary approach which successfully reproduces the meson meson phase shifts and generates the $f_0$ and $σ$ resonances in vacuum. We address here a new variety of mechanisms recently suggested to modify the $ππ$ interaction in the medium, as well as the role of the $s-$wave selfenergy, in addition to the $p-$wave, in the dressing of the pion propagators.

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arXiv2005

Chiral dynamics of hadrons in nuclei

In this talk I report on selected topics of hadron modification in the nuclear medium using the chiral unitary approach to describe the dynamics of the problems. I shall mention how antikaons, $η$, and $ϕ$ are modified in the medium and will report upon different experiments done or planned to measure the $ϕ$ width in the medium.

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arXiv2005

Two-meson cloud contribution to the baryon antidecuplet self-energy

We study the self-energy of the SU(3) antidecuplet coming from two-meson virtual clouds. Assuming that the exotic Theta+ belongs to an antidecuplet representation with N(1710) as nucleon partner, we derive effective Lagrangians that describe the decay of N(1710) into N pi pi with two pions in s- or p-wave. It is found that the self-energies for all members of the antidecuplet are attractive, and the larger strangeness particle is more bound. From two-meson cloud, we obtain about 20 % of the empirical mass splitting between states with different strangeness.

hep-ph↗

arXiv2005

Bound states of $Θ^+$ in nuclei

We study the binding energy and the width of the $Θ^+$ in nuclei, associated to the $K N$ and $ K πN$ components. The first one leads to negligible contributions while the second one leads to a sizeable attraction, enough to bind the $Θ^+$ in nuclei. Pauli blocking and binding effects on the $K N$ decay reduce considerably the $Θ^+$ decay width in nuclei and medium effects associated to the $ K πN$ component also lead to a very small width, as a consequence of which one finds separation between the bound levels considerably larger than the width of the states.

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arXiv2005

$Θ^+$ Hypernuclei

We present results for the selfenergy of the $Θ^+$ pentaquark in nuclei associated with two sources: the $KN$ decay of the $Θ^+$ and the two meson baryon decay channels of the $Θ^+$ partners in an antidecuplet of baryons. The first source is shown to produce a small potential, unable to bind the $Θ^+$ in nuclei, while the second source gives rise to a large attractive potential. At the same time we show that the width of the $Θ^+$ in nuclei is small, such that, in light and medium nuclei, many bound $Θ^+$ states would appear with a separation between levels appreciably larger than the width of the states, thus creating an ideal scenario for pentaquark spectroscopy in nuclei.

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arXiv2005

Baryonic Resonances from Baryon Decuplet-Meson Octet Interactions and the Exotic Resonance S=1, I=1, J^P=3/2-

Using the lowest order chiral Lagrangian we study s-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons. We find two bound states in the flavour SU(3) limit corresponding to the octet and decuplet representations. These are found to split into eight different trajectories in the complex plane when the SU(3) symmetry is broken gradually. Finally, we are able to provide a reasonable description for a good number of 4-star 3/2- resonances listed by the Particle Data Group. In particular, the Xi(1820), the Lambda(1520) and the Sigma(1670) states are well reproduced. We predict a few other resonances and also evaluate the couplings of the observed resonances to the various channels from the residues at the poles of the scattering matrix from where partial decay widths into different channels can be evaluated.

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arXiv2005

Resonances from Baryon decuplet-Meson octet interaction

The s-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons is studied in a unitarized coupled channel approach. We obtain a fair agreement for mass and width of several 3/2- resonances. In particular, the Xi(1820), the Lambda(1520) and the Sigma(1670) states are well reproduced. Other resonances are predicted and also the couplings of the observed resonances to the various channels are evaluated.

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arXiv2005

Determining the $Θ^+$ quantum numbers through a Kaon induced reaction

We study the $K^+p\to π^+KN$ reaction with kinematical condition suited to the production of the $Θ^+$ resonance. It is shown that in this reaction with the polarization experiment, a combined consideration of the strength at the peak and the angular dependence of cross section can help determine the $Θ^+$ quantum numbers.

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arXiv2005

Baryonic Resonances from Baryon Decuplet-Meson Octet Interaction

We study $S$-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons using the lowest order chiral Lagrangian. In the S=1 sector, we find an attractive interaction in the $ΔK$ channel with I=1 while it is repulsive for I=2. The attractive interaction leads to a pole in the second Riemann sheet of the complex plane and is manifested as a large strength in the scattering amplitude close to the $ΔK$ threshold, which is not the case for I=2. We use the unitarized coupled channel approach to also investigate all the other possible values of strangeness and isospin. We find two bound states in the SU(3) limit corresponding to the octet and decuplet representations. These are found to split into eight different trajectories in the complex plane when the SU(3) symmetry is broken gradually. Finally, we are able to provide a reasonable description for a good number of 4-star ${3/2}^-$ resonances listed by the Particle Data Group. In particular, the $Ξ(1820)$, the $Λ(1520)$ and the $Σ(1670)$ states are well reproduced. We predict a few other resonances and also evaluate the couplings of the observed resonances to the various channels from the residues at the poles of the scattering matrix from where partial decay widths into different channels can be evaluated.

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arXiv2004

$Θ^+$ pentaquark in the nuclear medium

We study the interaction of the $Θ^+$ pentaquark with nuclear matter associated to the $KN$ decay channels and to the two meson cloud. We find that the potential is attractive and could be strong enough to lead to the existence of $Θ^+$ nuclear bound states.

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arXiv2004

Radiative vector meson decay

We study the radiative $ρ$, $ω$ and $ϕ$ decay into $π^0 π^0 γ$ and $π^0 ηγ$ taking into account mechanisms in which there are two sequential vector-vector-pseudoscalar or axial-vector--vector--pseudoscalar steps followed by the coupling of a vector meson to the photon, considering the final state interaction of the two mesons. Other mechanisms in which two kaons are produced through the same sequential mechanisms or from vector meson decay into two kaons which undergo final state interaction leading to the final pair of pions or $π^0 η$, are also considered. The results of the parameter free theory, together with the theoretical uncertainties, are compared with the latest experimental results at Frascati and Novosibirsk.

hep-ph↗

arXiv2004

Dynamically Generated Resonances in the Chiral Unitary Approach to Meson Baryon Interaction

In this talk we report on the use of a chiral unitary approach for the interaction of the octets of meson and baryon and the octet of mesons with the decuplet of baryons. Two octets of $J^π=1/2^-$ baryon states and a singlet are generated dynamically in the first case, resulting in the case of strangeness $S=-1$ in two poles of the scattering matrix close to the nominal $Λ(1405)$ resonance. In the second case many resonances are also generated, among them an exotic baryon with S=1 corresponding to a $ΔK$ resonance. We make suggestions of experiments which could show evidence for the existence of these states.

hep-ph↗