arXiv subjects

E. Oset

Publications and source records attributed to E. Oset.

At least 217 records · Page 12Linked to original sources

arXiv2012

The $KD$, $ηD_s$ interaction in finite volume and the nature of the $D_{s^* 0}(2317)$ resonance

An SU(4) extrapolation of the chiral unitary theory in coupled channels done to study the scalar mesons in the charm sector is extended to produce results in finite volume. The theory in the infinite volume produces dynamically the $D_{s^*0}(2317)$ resonance by means of the coupled channels $KD$, $ηD_s$. Energy levels in the finite box are evaluated and, assuming that they would correspond to lattice results, the inverse problem of determining the bound states and phase shifts in the infinite volume from the lattice data is addressed. We observe that it is possible to obtain accurate $KD$ phase shifts and the position of the $D_{s^*0}(2317)$ state, but it requires the explicit consideration of the two coupled channels in the analysis if one goes close to the $ηD_s$ threshold. We also show that the finite volume spectra look rather different in case the $D_{s^*0}(2317)$ is a composite state of the two mesons, or if it corresponds to a non molecular state with a small overlap with the two meson system. We then show that a careful analysis of the finite volume data can shed some light on the nature of the $D_{s^*0}(2317)$ resonance as a $KD$ molecule or otherwise.

hep-lat↗

arXiv2012

Effects of pseudoscalar-baryon channels in the dynamically generated vector-baryon resonances

We study the interaction of vector mesons with the octet of stable baryons in the framework of the local hidden gauge formalism using a coupled channels unitary approach, including also the pseudoscalar-baryon channels which couple to the same quantum numbers. We examine the scattering amplitudes and their poles, which can be associated to known $J^P=1/2^-,3/2^-$ baryon resonances, and determine the role of the pseudoscalar-baryon channels, changing the width and eventually the mass of the resonances generated with only the basis of vector-baryon states.

hep-ph↗

arXiv2012

Scattering of unstable particles in a finite volume: the case of pi rho scattering and the a1(1260) resonance

We present a way to evaluate the scattering of unstable particles quantized in a finite volume with the aim of extracting physical observables for infinite volume from lattice data. We illustrate the method with the $πρ$ scattering which generates dynamically the axial-vector $a_1(1260)$ resonance. Energy levels in a finite box are evaluated both considering the $ρ$ as a stable and unstable resonance and we find significant differences between both cases. We discuss how to solve the problem to get the physical scattering amplitudes in the infinite volume, and hence phase shifts, from possible lattice results on energy levels quantized inside a finite box.

hep-lat↗

arXiv2011

rho-rho-N and rho-rho-Delta molecules with $J^P=5/2^{+}$ and $J^P=7/2^{+}$

The rho-rho-N and rho-rho-Delta three-body systems have been studied within the framework of the fixed center approximation of Faddeev equation. The rho-rho interaction in isospin I=0, spin S=2 is strongly attractive, and so are the N-rho, Delta-rho interactions. This leads to bound states of both rho-rho-N and rho-rho-Delta. We find peaks of the modulus squared of the scattering matrix around 2227 MeV for rho-rho-N, and 2372 MeV for rho-rho-Delta. Yet, the strength of the peak for the rho-rho-N amplitude is much smaller than for rho-rho-Delta, weakening the case for a rho-rho-N bound state, or a dominant rho-rho-N component. A discussion is made on how these states can be searched for in present programs looking for multimeson final states in different reactions.

nucl-th↗

arXiv2011

Nuclear medium effects on the $\bar K^*$ meson

The $\bar K^*$ meson in dense matter is analyzed by means of a unitary approach in coupled channels based on the local hidden gauge formalism. The $\bar K^*$ self-energy and the corresponding $\bar K^*$ spectral function in the nuclear medium are obtained. We observe that the $\bar K^*$ develops a width in matter up to five times bigger than in free space. We also estimate the transparency ratio of the $γA \to K^+ K^{*-} A^\prime$ reaction. This ratio is an excellent tool to detect experimentally modifications of the $\bar K^*$ meson in dense matter.

nucl-th↗

arXiv2011

eta-prime nucleus optical potential and possible eta-prime bound states

Starting from a recent model of the eta'N interaction, we evaluate the eta'-nucleus optical potential, including the contribution of lowest order in density, t rho/2m_eta', together with the second order terms accounting for eta' absorption by two nucleons. We also calculate the formation cross section of the eta' bound states from (pi+,p) reactions on nuclei. The eta'-nucleus potential suffers from uncertainties tied to the poorly known eta'N interaction, which can be partially constrained by the experimental modulus of the eta'N scattering length and/or the recently measured transparency ratios in eta' nuclear photoproduction. Assuming an attractive interaction and taking the claimed experimental value |a_eta'N| = 0.1 fm, we obtain a eta' optical potential in nuclear matter at saturation density of V_eta' = -(8.7 + 1.8i) MeV, not attractive enough to produce eta' bound states in light nuclei. Larger values of the scattering length give rise to deeper optical potentials, with moderate enough imaginary parts. For a value |a_eta'| = 0.3 fm, which can still be considered to lie within the uncertainties of the experimental constraints, the spectra of light and medium nuclei show clear structures associated to eta'-nuclear bound states and to threshold enhancements in the unbound region.

hep-ph↗

arXiv2011

Two, three, many body systems involving mesons

In this talk we show recent developments on few body systems involving mesons. We report on an approach to Faddeev equations using chiral unitary dynamics, where an explicit cancellation of the two body off shell amplitude with three body forces stemming from the same chiral Lagrangians takes place. This removal of the unphysical off shell part of the amplitudes is most welcome and renders the approach unambiguous, showing that only on shell two body amplitudes need to be used. Within this approach, systems of two mesons and one baryon are studied, reproducing properties of the low lying $1/2^+$ states. On the other hand we also report on multirho and $K^*$ multirho states which can be associated to known meson resonances of high spin.

nucl-th↗

arXiv2011

Unitarized Chiral Perturbation Theory in a finite volume: scalar meson sector

We develop a scheme for the extraction of the properties of the scalar mesons f0(600), f0(980), and a0(980) from lattice QCD data. This scheme is based on a two-channel chiral unitary approach with fully relativistic propagators in a finite volume. In order to discuss the feasibility of finding the mass and width of the scalar resonances, we analyze synthetic lattice data with a fixed error assigned, and show that the framework can be indeed used for an accurate determination of resonance pole positions in the multi-channel scattering.

hep-lat↗

arXiv2011

The pp->p Lambda K+ and pp->p Sigma0 K+ reactions with chiral dynamics

We report on a theoretical study of the pp->p Lambda K+ and pp->p Sigma0 K+ reactions near threshold using a chiral dynamical approach. The production process is described by single-pion and single-kaon exchange. The final state interactions of nucleon-hyperon, K-hyperon and K-nucleon systems are also taken into account. We show that our model leads to a fair description of the experimental data on the total cross section of the pp->p Lambda K+ and pp->p Sigma0 K+ reactions. We find that the experimental observed strong suppression of Sigma0 production compared to Lambda production at the same excess energy can be explained. However, ignorance of phases between some amplitudes does not allow to properly account for the nucleon-hyperon final state interaction for the pp->p Sigma0 K+ reaction. We also demonstrate that the invariant mass distribution and the Dalitz plot provide direct information about the Lambda and Sigma0 production mechanism, and can be tested by experiments at COSY or HIRFL-CSR.

nucl-th↗

arXiv2011

$NDK$, $\bar{K} DN$ and $ND\bar{D}$ molecules

We investigate theoretically baryon systems made of three hadrons which contain one nucleon and one D meson, and in addition another meson, $\bar{D}, K$ or $\bar{K}$. The systems are studied using the Fixed Center Approximation to the Faddeev equations. The study is made assuming scattering of a $K$ or a $\bar{K}$ on a $DN$ cluster, which is known to generate the $Λ_c(2595)$, or the scattering of a nucleon on the $D\bar{D}$ cluster, which has been shown to generate a hidden charm resonance named X(3700). We also investigate the configuration of scattering of $N$ on the $KD$ cluster, which is known to generate the $D_{s0}^*(2317)$. In all cases we find bound states, with the $NDK$ system, of exotic nature, more bound than the $\bar{K} DN$.

hep-ph↗

arXiv2011

The pp -> p Lambda K+ and pp -> p Sigma0 K+ Reactions in the Chiral Unitary Approach

We study the pp -> p Lambda K+ and pp -> p Sigma0 K+ reactions near threshold by using a chiral unitary approach. We consider the single-pion and single-kaon exchange as well as the final state interactions of nucleon-hyperon, K-hyperon and K-nucleon systems. Our results on the total cross section of the pp -> p Lambda K+ reaction is consistent with the experimental data, and the experimental observed strong suppression of Sigma0 production compared to Lambda production at the same excess energy can also be explained in our model.

nucl-th↗

arXiv2011

Chiral unitary theory of scalar mesons in a finite volume

We develop a scheme for the extraction of the properties of the scalar mesons $f_0(600)$, $f_0(980)$, and $a_0(980)$ from lattice QCD data. This scheme is based on a two-channel chiral unitary approach with fully relativistic propagators in a finite volume. In order to discuss the feasibility of finding the mass and width of the scalar resonances, we analyze synthetic lattice data with a fixed error assigned, and show that the framework can be indeed used for an accurate determination of resonance pole positions in the multi-channel scattering.

hep-lat↗

arXiv2011

The K d -> Lambda(1405) n reaction with the DAFNE set up and the $\bar{K}NN$ system revisited

The $K^{-}$ induced production of $Λ(1405)$ in the $K^{-} d \to πΣn$ reaction is investigated having in mind the conditions of the DAFNE facility at Frascati. We find that the fastest kaons from the decay of the $ϕ$ at DAFNE are well suited to see this resonance if one selects forward going neutrons in the center of mass, which reduce the contribution of single scattering and stress the contribution of the double scattering where the signal of the resonance appears clearer. We take advantage to report briefly on a recent work in which in addition to the $\bar{K}NN$ system with total spin S=0, we find a less bound state (although with equally large width) with S=1, like in the $K^{-} d$ reported in the first part.

nucl-th↗

arXiv2011

A new perspective on the $Δ_{5/2^{+}}(2000)$ puzzle

We argue that $Δ_{5/2^{+}}(2000)(\ast\ast),$ cataloged as a resonance in the Particle Data Book Review (PDG), should be interpreted instead as two distinctive resonances, $Δ_{5/2^{+}}(\sim1740)$ and $Δ_{5/2^{+}}(\sim2200)$. Our argument is based on a solution of the $πΔρ$ problem in a Fixed Center Approximation (FCA) to the Fadeev equations. $Δ_{5/2^{+}}(\sim1740)$ can then be interpreted as a $π-(Δρ)_{N(1675)}$ bound state. As a corollary $Δ_{1/2^{+}}(1750)(\ast)$ can be understood as a $πN_{1/2^{-}}(1650)$ bound state.

nucl-th↗

arXiv2011

Chiral unitary approach to η' N scattering at low energies

We study the η' N interaction within a chiral unitary approach which includes πN, ηN and related pseudoscalar meson-baryon coupled channels. Since the SU(3) singlet does not contribute to the standard interaction and the η' is mostly a singlet, the resulting scattering amplitude is very small and inconsistent with experimental estimations of the η' N scattering length. The additional consideration of vector meson-baryon states into the coupled channel scheme, via normal and anomalous couplings of pseudoscalar to vector mesons, enhances substantially the η' N amplitude. We also exploit the freedom of adding to the Lagrangian a new term, allowed by the symmetries of QCD, which couples baryons to the singlet meson of SU(3). Adjusting the unknown strength to the η' N scattering length, we obtain predictions for the elastic η' N --> η' N and inelastic η' N --> ηN, πN, KΛ, KΣ cross sections at low η' energies, and discuss their significance.

nucl-th↗

arXiv2011

The $\bar{K}NN$ system with chiral dynamics

We have performed a calculation of the scattering amplitude for the three body system $\bar{K}NN$ assuming $\bar{K}$ scattering against a $NN$ cluster, using the Fixed Center approximation to the Faddeev equations. The $\bar{K}N$ amplitudes, which we take from chiral unitary dynamics, govern the reaction and we find a $\bar{K}NN$ amplitude that peaks around 40 MeV below the $\bar{K}NN$ threshold, with a width in $|T|^2$ of the order of 50 MeV for spin 0 and has another peak around 27 MeV with similar width for spin 1. The results are in line with those obtained using different methods but implementing chiral dynamics. The simplicity of the approach allows one to see the important ingredients responsible for the results. In particular we show the effects from the reduction of the size of the $NN$ cluster due to the interaction with the $\bar{K}$ and those from the explicit considiration of the $ πΣN $ channel in the three body equations.

hep-ph↗

arXiv2011

Faddeev fixed-center approximation to the $N\bar{K}K$ system and the signature of a $N^*(1920)(1/2^+)$ state

We perform a calculation for the three body $N \bar{K} K$ scattering amplitude by using the fixed center approximation to the Faddeev equations, taking the interaction between $N$ and $\bar{K}$, $N$ and $K$, and $\bar{K}$ and $K$ from the chiral unitary approach. The resonant structures show up in the modulus squared of the three body scattering amplitude and suggest that a $N\bar{K}K$ hadron state can be formed. Our results are in agreement with others obtained in previous theoretical works, which claim a new $N^*$ resonance around 1920 MeV with spin-parity $J^P=1/2^+$. The existence of these previous works allows us to test the accuracy of the fixed center approximation in the present problem and sets the grounds for possible application in similar problems, as an explorative tool to determine bound or quasibound three hadron systems.

nucl-th↗

arXiv2011

Delta rho pi interaction leading to N* and Delta* resonances

We have performed a calculation for the three body $Δρπ$ system by using the fixed center approximation to Faddeev equations, taking the interaction between $Δ$ and $ρ$, $Δ$ and$π$, and $ρ$ and $π$ from the chiral unitary approach. We find several peaks in the modulus squared of the three-body scattering amplitude, indicating the existence of resonances, which can be associated to known $I=1/2, 3/2$ and $J^P=1/2^+, 3/2^+$ and $5/2^+$ baryon states.

nucl-th↗