arXiv subjects

E. Oset

Publications and source records attributed to E. Oset.

At least 361 records · Page 20Linked to original sources

arXiv2006

Two pion mediated scalar isoscalar NN interaction in the nuclear medium

We study the modification of the nucleon nucleon interaction in a nuclear medium in the scalar isoscalar channel, mediated by the exchange of two correlated ($σ$ channel) or uncorrelated pions. For this purpose we use a standard approach for the renormalization of pions in nuclei. The corrections obtained for the $NN$ interaction in the medium in this channel are of the order of 20% of the free one in average, and the consideration of short range correlations plays an important role in providing these moderate changes. Yet, the corrections are sizable enough to suggest further studies of the stability and properties of nuclear matter.

nucl-th↗

arXiv2006

$A$ dependence of the $γ$- and $p$-induced production of the $Λ(1520)$ from nuclei

Using results of a recent calculation of the $Λ(1520)$ in the nuclear medium, which show that the medium width is about five times the free width, we study the A dependence of the $Λ(1520)$ production cross section in the reactions $γ~A \to K^+ Λ(1520) A^\prime$ and $p~ A \to p~ K^+ Λ(1520) A^\prime$. We find a sizable A dependence in the ratio of the nuclear cross sections for heavy nuclei with respect to a light one due to the large value of the $Λ(1520)$ width in the medium, showing that devoted experiments, easily within reach in present facilities, can provide good information on that magnitude by measuring the cross sections studied here.

nucl-th↗

arXiv2005

$Λ(1520)$ at finite density

We study the decay channels of the $Λ(1520)$ in a nuclear medium and find a sizable change - of the order of factor five - of the width of this hyperon at normal nuclear matter density. The mass shift of the $Λ(1520)$ is moderate.

nucl-th↗

arXiv2005

A critical analysis on deeply bound kaonic states in nuclei

We make a critical analysis on the theoretical calculations that lead to predictions of deeply bound kaonic states in nuclei. The model set-up, after dropping several important processes and channels, leads unavoidably to an unrealistic deep potential with a very small imaginary part. We review also the experimental results taken as reference for the claim of deeply bound kaons. We suggest that the peaks of the proton spectra come from $K^-$ absorption on a pair of nucleons, leaving the rest of the nucleons as spectators. Based on this conjecture we predict what would happen in other nuclei.

nucl-th↗

arXiv2005

On the nature of the Lambda(1405) as a superposition of two states

We use recent data on the $K^- p \to π^0 π^0 Σ^0$ reaction with the $π^0 Σ^0$ mass distribution of forming the $Λ(1405)$ with a peak at 1420 MeV and a relatively narrow width of $Γ= 38$ MeV, together with those of the $π^- p \to K^0 πΣ$ reaction to show that there are two $Λ(1405)$ states instead of one as so far assumed.

hep-ph↗

arXiv2005

Baryonic Resonances from the Interactions of the Baryon Decuplet and Meson Octet

We study $S$-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons using the lowest order chiral Lagrangian. 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.

nucl-th↗

arXiv2005

Evidence for two Lambda(1405) resonance states

The $K^- p \to π^0 π^0 Σ^0$ reaction is studied within a chiral unitary model. The distribution of $π^0 Σ^0$ states forming the $Λ(1405)$ shows, in agreement with a recent experiment, a peak at 1420 MeV and a relatively narrow width of $Γ= 38$ MeV. We use these data in combination with those of the $π^- p \to K^0 πΣ$ reaction and elements of chiral unitary theory to prove that there are two $Λ(1405)$ states instead of one as so far assumed.

nucl-th↗

arXiv2005

Chiral dynamics of the $Λ(1520)$ in coupled channels tested in the $K^-p\toππΛ$ reaction

The $Λ(1520)$ resonance is generated dynamically in a unitary coupled channel framework with the $πΣ^*$ and $KΞ^*$ channels in s-wave and $πΣ$ and $\bar K N$ channels in d-wave. The dynamics of this resonance close to and above threshold is then tested through the reactions $K^-p\toππΛ$ and a good agreement with the experimentally measured cross section is observed.

nucl-th↗

arXiv2005

$Λ(1520)$ and $Σ(1385)$ in the nuclear medium

Recent studies of the $Λ(1520)$ resonance within chiral unitary theory with coupled channels find the resonance as a dynamically generated state from the interaction of the decuplet of baryons and the octet of mesons, essentially a quasibound state of $πΣ^*(1385)$ in this case, although the coupling of the $Λ(1520)$ to the $\bar{K}N$ and $πΣ$ makes this picture only approximate. The $πΣ^*(1385)$ decay channel of the $Λ(1520)$ is forbidden in free space for the nominal mass of the $Σ^*(1385)$, but the coupling of the $π$ to $ph$ components in the nuclear medium opens new decay channels of the $Λ(1520)$ in the nucleus and produces a much larger width. Together with medium modifications of the $\bar{K}N$ and $πΣ$ decay channels, the final width of the $Λ(1520)$ at nuclear matter density is more than five times bigger than the free one. We perform the calculations by dressing simultaneously the $Λ(1520)$ and the $Σ^*(1385)$ resonances, finding moderate changes in the mass but substantial ones in the width of both resonances.

nucl-th↗

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.

nucl-th↗

arXiv2005

Discussion of the eta to pi^0 gamma gamma decay within a chiral unitary approach

We improve the calculations of the $η\to π^0 γγ$ decay within the context of meson chiral lagrangians. We use a chiral unitary approach for the meson-meson interaction, thus generating the $a_0(980)$ resonance and fixing the longstanding sign ambiguity on its contribution. This also allows us to calculate the loops with one vector meson exchange, thus removing a former source of uncertainty. In addition we ensure the consistency of the approach with other processes. First, by using vector meson dominance couplings normalized to agree with radiative vector meson decays. And, second, by checking the consistency of the calculations with the related $γγ\to π^0 η$ reaction. We find an $η\to π^0 γγ$ decay width of $0.47\pm 0.10$ eV, in clear disagreement with published data but in remarkable agreement with the most recent measurement.

hep-ph↗

arXiv2005

Chiral dynamics in "gamma p --> pi^0 eta p" and related reactions

Using a chiral unitary approach for meson-baryon scattering in the strangeness zero sector, where the $N^*(1535)$ and $Δ^*(1700)$ resonances are dynamically generated, we study the reactions $γp \to π^0 ηp$ and $γp \to π^0 K^0 Σ^+$ at photon energies at which the final states are produced close to threshold. Among several reaction mechanisms, we find the most important is the excitation of the $Δ^*(1700)$ state which subsequently decays into a pseudoscalar meson and the $N^*(1535)$. Hence, the reaction provides useful information with which to test current theories of the dynamical generation of the low-lying $1/2^-$ and $3/2^-$ states. Predictions are made for cross sections and invariant mass distributions which can be compared with forthcoming experiments at ELSA.

nucl-th↗

arXiv2005

Two pole structure of the Lambda(1405) resonance

The K^- p --> pi^0 pi^0 Sigma^0 reaction is studied within a chiral unitary model. The distribution of pi^0 Sigma^0 states forming the Lambda(1405) shows, in agreement with a recent experiment, a peak at 1420 MeV and a relatively narrow width of 38 MeV. This reaction gives maximal possible weight to the second Lambda(1405) state found in chiral unitary theories, which is narrow and of higher energy than the nominal Lambda(1405). In contrast, the pi^- p --> K^0 pi Sigma reaction gives more weight to the pole at lower energy and with a larger width. The data of these two experiments, together with the present theoretical analysis, provides for the first time a clear experimental evidence of the two pole structure of the Lambda(1405).

hep-ph↗

arXiv2005

Low lying axial-vector mesons as dynamically generated resonances

We make a theoretical study of the s-wave interaction of the nonet of vector mesons with the octet of pseudoscalar mesons starting from a chiral invariant Lagrangian and implementing unitarity in coupled channels. By looking for poles in the unphysical Riemann sheets of the unitarized scattering amplitudes, we get two octets and one singlet of axial-vector dynamically generated resonances. The poles found can be associated to most of the low lying axial-vector resonances quoted in the Particle Data Book: $b_1(1235)$, $h_1(1170)$, $h_1(1380)$, $a_1(1260)$, $f_1(1285)$ and two poles to the $K_1(1270)$ resonance. We evaluate the couplings of the resonances to the $VP$ states and the partial decay widths in order to reinforce the arguments in the discussion.

hep-ph↗

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

The $ϕ$ meson width in the medium from proton induced $ϕ$ production in nuclei

We perform calculations for the production of $ϕ$ mesons in nuclei at energies just above threshold and study the $A$ dependence of the cross section. We use results for the $ϕ$ selfenergy in the medium obtained within a chiral unitary approach. We find a strong $A$ dependence which is tied to the distortion of the incident proton and to the absorption of the $ϕ$ in its way out of the nucleus. The effect of this latter process reduces the cross section in about a factor two in heavy nuclei proving that the $A$ dependence of the cross section bears valuable information on the $ϕ$ width in the nuclear medium. Calculations are done for energies which are accessible in an experimental facility like COSY.

nucl-th↗

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.

nucl-th↗

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↗