arXiv subjects

E. Oset

Publications and source records attributed to E. Oset.

At least 307 records · Page 17Linked to original sources

arXiv2008

The ρρinteraction in the hidden gauge formalism and the f_0(1370) and f_2(1270) resonances

We have studied the interaction of vectors mesons within the hidden gauge formalism and applied it to the particular case of the $ρρ$ interaction. We find a strong attraction in the isospin, spin channels I,S=0,0 and 0,2, which is enough to bind the $ρρ$ system. We also find that the attraction in the I,S=0,2 channel is much stronger than in the 0,0 case. The states develop a width when the $ρ$ mass distribution is considered, and particularly when the $ππ$ decay channel is turned on. Using a regularization scheme with cut offs of natural size, we obtain results in fair agreement with the mass and the width of the $f_0(1370)$ and $f_2(1270)$ meson states, providing a natural explanation of why the tensor state is more bound than the scalar and offering a new picture for these states, which would be dynamically generated from the $ρρ$ interaction or, in simpler words, $ρρ$ molecular states.

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arXiv2008

Testing the nature of the $Λ$(1520) in the $J/ψ\to\barΛK^-p$ and $J/ψ\to\barΛπ^+π^-Λ$ reactions

We study the reactions $J/ψ\to\barΛK^-p$ and $J/ψ\to\barΛπ^+π^-Λ$ with a unitary chiral approach. We predict the ratio of the invariant mass distributions of these two reactions at the $Λ(1520)$ peak position, which is free of the unknown production mechanism and reflects only the properties of the $Λ(1520)$. An experimental measurement of this ratio will provide the couplings of the $Λ(1520)$ to its decay channels, allowing to test the predictions of the chiral unitary approach on this resonance, which appears as dynamically generated in that approach.

hep-ph↗

arXiv2008

Nature of the axial-vector mesons from their Nc behavior within the chiral unitary approach

By describing within the chiral unitary approach the s-wave interaction of the vector meson nonet with the octet of pseudoscalar Goldstone Bosons, we find that the main component of the axial vector mesons b_1(1235), h_1(1170), h_1(1380), a_1(1260), f_1(1285) and the two states associated to the K_1(1270) does not follow the QCD dependence on the number of colors for ordinary qqbar mesons.

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arXiv2008

X(2175) as a resonant state of the $ϕK \bar{K}$ system

We perform a Faddeev calculation for the three mesons system, $ϕK \bar{K}$, taking the interaction between two pseudoscalar mesons and between a vector and a pseudoscalar meson from the chiral unitary approach. We obtain a neat resonance peak around a total mass of 2150 MeV and an invariant mass for the $K \bar{K}$ system around 970 MeV, very close to the $f_0(980)$ mass. The state appears in I=0 and qualifies as a $ϕf_0(980)$ resonance. We enlarge the space of states including $ϕππ$, since $ππ$ and $K \bar{K}$ build up the $f_0$ (980), and find moderate changes that serve to quantify theoretical uncertainties. No state is seen in I=1. This finding provides a natural explanation for the recent state found at BABAR and BES, the X(2175), which decays into $ϕf_0(980)$.

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arXiv2008

Hidden gauge formalism for the radiative decays of axial-vector mesons

The radiative decay of the axial-vector resonances into a pseudoscalar meson and a photon is studied using the vector meson Lagrangian obtained from the hidden gauge symmetry (HGS) formalism. The formalism is well suited to study this problem since it deals with pseudoscalar and vector mesons in a unified way, respecting chiral invariance. We show explicitly the gauge invariance of the set of diagrams that appear in the approach and evaluate the radiative decay width of the a1(1260) and b1(1235) axial vector meson resonances into pi gamma. We also include the contribution of loops involving anomalous couplings and compare the results to those obtained previously within another formalism.

hep-ph↗

arXiv2008

The role of the N*(1535) resonance and the pi^- p --> KY amplitudes in the OZI forbidden pi N --> phi N reaction

We study the pi N --> phi N reaction close to the phi N threshold within the chiral unitary approach, by combining the pi^- p --> K^+ Sigma^-, pi^- p --> K^0 Sigma^0 and pi^- p --> K^0 Lambda amplitudes with the coupling of the phi to the K components of the final states of these reactions via quantum loops. We obtain a good agreement with experiment when the dominant pi^- p --> K^0 Lambda amplitude is constrained with its experimental cross section. We also evaluate the coupling of the N*(1535) to phi N and find a moderate coupling as a consequence of partial cancellation of the large KY components of the N*(1535). We also show that the N*(1535) pole approximation is too small to reproduce the measured cross section for the pi N --> phi N reaction.

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arXiv2008

Critical review of [K- ppn] bound states

We make a thorough study of the process of three body kaon absorption in nuclei, in connection with a recent FINUDA experiment which claims the existence of a deeply bound kaonic state from the observation of a peak in the Lambda d invariant mass distribution following K- absorption on Li6. We show that the peak is naturally explained in terms of K- absorption from three nucleons leaving the rest as spectators. We can also reproduce all the other observables measured in the same experiment and used to support the hypothesis of the deeply bound kaon state. Our study also reveals interesting aspects of kaon absorption in nuclei, a process that must be understood in order to make progress in the search for K- deeply bound states in nuclei.

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arXiv2008

Transition form factors of the N*(1535) as a dynamically generated resonance

We discuss how electromagnetic properties provide useful tests of the nature of resonances, and we study these properties for the N*(1535) which appears dynamically generated from the strong interaction of mesons and baryons. Within this coupled channel chiral unitary approach, we evaluate the A_1/2 and S_1/2 helicity amplitudes as a function of Q^2 for the electromagnetic N*(1535) to gamma* N transition. Within the same formalism we evaluate the cross section for the reactions gamma N to eta N. We find a fair agreement for the absolute values of the transition amplitudes, as well as for the Q^2 dependence of the amplitudes, within theoretical and experimental uncertainties discussed in the paper. The ratios obtained between the S_1/2 and A_1/2 for the neutron or proton states of the N*(1535) are in qualitative agreement with experiment and there is agreement on the signs. The same occurs for the ratio of cross sections for the eta photoproduction on neutron and proton targets in the vicinity of the N*(1535) energy. The global results support the idea of this resonance as being dynamically generated, hence, largely built up from meson baryon components. However, the details of the model indicate that an admixture with a genuine quark state is also demanded that could help obtain a better agreement with experimental data.

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arXiv2008

Chiral Unitary Dynamics of Hadrons and Hadrons in a Nuclear Medium

In this talk I summarize recent findings around the description of axial vector mesons as dynamically generated states from the interaction of pseudoscalar mesons and vector mesons, dedicating some attention to the two $K_1(1270)$ states. Then I review the generation of open and hidden charm scalar and axial states, and how some recent experiment supports the existence of the new hidden charm scalar state predicted. I present recent results showing that the low lying $1/2^+$ baryon resonances for S=-1 can be obtained as bound states or resonances of two mesons and one baryon in coupled channels. Then show the differences with the S=0 case, where the $N^*(1710)$ appears also dynamically generated from the two pion one nucleon system, but the $N^*(1440)$ does not appear, indicating a more complex structure of the Roper resonance. Finally I shall show how the state X(2175), recently discovered at BABAR and BES, appears naturally as a resonance of the $ϕK \bar{K}$ system.

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arXiv2008

Three-body hadronic structure of low-lying $1/2^+$ $Σ$ and $Λ$ resonances

We discuss the dynamical generation of some low-lying $1/2^+$ $Σ$'s and $Λ$'s in two-meson one-baryon systems. These systems have been constructed by adding a pion in $S$-wave to the $\bar{K} N$ pair and its coupled channels, where the $1/2^-$ $Λ$(1405)-resonance gets dynamically generated. We solve Faddeev equations in the coupled-channel approach to calculate the $T$-matrix for these systems as a function of the total energy and the invariant mass of one of the meson-baryon pairs. This squared $T$-matrix shows peaks at the energies very close to the masses of the strangeness -1, $1/2^+$ resonances listed in the particle data book.

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arXiv2008

The $σK$ coupling in the chiral unitary approach and the isoscalar $\bar{K}N$, $\bar{K}A$ interaction

We evaluate the "$σ$" exchange contribution to the $\bar{K}N\to\bar{K}N$ scattering within a chiral unitary approach. We show that the chiral transition potentials for $ππ\to K \bar{K}$ in the $t$-channel lead to a "$σ$" contribution that vanishes in the $\bar{K}$ forward direction and, hence, would produce a null "$σ$" exchange contribution to the $K^-$ optical potential in nuclear matter in a simple impulse approximation. This is a consequence of the fact that the leading order chiral Lagrangian gives an I=0 $ππ\to K\bar{K}$ amplitude proportional to the squared momentum transfer, $q^2$. This finding poses questions on the meaning or the origin of "$σ$" exchange potentials used in relativistic mean field approaches to the $K^-$ nuclear selfenergy. This elementary "$σ$" exchange potential in $\bar{K}N\to\bar{K}N$ is compared to the Weinberg-Tomozawa term and is found to be smaller than present theoretical uncertainties but will be relevant in the future when aiming at fitting increasingly more accurate data.

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arXiv2008

The radiative decay of $ψ(3770)$ into the predicted scalar state X(3700)

We calculate the radiative decay width of the $ψ(3770)$ into the dynamically generated scalar resonance X(3700) which is predicted in a previous paper. The results show that it is possible that the upgraded BEPC-II facility will generate enough statistics in order to observe this decay and thus confirm the existence of the X(3700).

hep-ph↗

arXiv2008

The $N^*(1710)$ as a resonance in the $ππN$ system

We study the $ππN$ system by solving the Faddeev equations, for which the input two-body $t$-matrices are obtained by solving the Bethe-Salpeter equation in the coupled channel formalism. The potentials for the $ππ$, $πN$ sub-systems and their coupled channels are obtained from chiral Lagrangians, which have been earlier used to study resonances in these systems successfully. In this work, we find a resonance in the $ππN$ system with a mass of $1704 - i 375/2$ MeV and with quantum numbers $I=1/2$, $J^π=1/2^+$. We identify this state with the $N^*(1710)$. This peak is found where the energies of the $ππ$ sub-system fall in the region of the $σ$ resonance. We do not find evidence for the Roper resonance in our study indicating a more complex structure for this resonance, nor for any state with total isospin $I=3/2$ or $5/2$.

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arXiv2008

The $e^+e^-\to J/ψD \bar D$, $J/ψD\bar D^*$ reactions with dynamically generated resonances

In two recent reactions by Belle producing $D\bar D$ and $D\bar D^*$ meson pairs, peaks above threshold have been measured in the differential cross sections, possibly indicating new resonances in these channels. We want to study such reactions from the point of view that the $D$ meson pairs are produced from already known or predicted resonances below threshold. Our study shows that the peak in the $D\bar D^*$ production is not likely to be caused by the X(3872) resonance, but the peak seen in $D\bar D$ invariant mass can be well described if the $D\bar D$ pair comes from the already predicted scalar X(3700) resonance.

hep-ph↗

arXiv2008

Three body resonances in two meson-one baryon systems

We report four $Σ$'s and three $Λ$'s, in the 1500 - 1800 MeV region, as two meson - one baryon S-wave $(1/2)^+$ resonances. We solve Faddeev equations in the coupled channel approach. The invariant mass of one of the meson-baryon pairs and that of the three particles have been varied and peaks in the squared three body $T$-matrix have been found very close to the existing $S$ = -1, $J^P= 1/2^+$ low lying baryon resonances. The input two-body $t$-matrices for meson-meson and meson-baryon interaction have been calculated by solving the Bethe-Salpeter equation with the potentials obtained in the chiral unitary approach.

nucl-th↗

arXiv2008

On the role of meson loops in the $f_0(1710)$ decay into $Vγ$

We investigate the relevance of the meson loops in the $f_0(1710)$ scalar meson decay into one photon and one vector meson, ($ρ$, $ω$ and $ϕ$). In particular we estimate the size of the loops coming from the decay of the $f_0(1710)$ into two pseudoscalar mesons, containing three pseudoscalar mesons in the loop or two pseudoscalar and one vector meson. The results, despite having large uncertainties, manifest that the contribution of the meson loops to these radiative decays is quite relevant and should be taken into account by the theoretical calculations which use this observables as a test of the possible glueball nature of this resonance.

hep-ph↗

arXiv2008

Axial Resonances in the Open and Hidden Charm Sectors

A SU(4) flavor symmetrical Lagrangian is constructed for the interaction of the pseudo-scalar mesons with the vector mesons. SU(4) symmetry is broken to SU(3) by suppression of terms in the Lagrangian where the interaction should be driven by charmed mesons. Chiral symmetry can be restored by setting this new SU(4) symmetry breaking parameters to zero. Unitarization in coupled channels leads to the dynamical generation of resonances. Many known axial resonances can be identified including the new controversial X(3872) and the structure found recently by Belle around 3875 MeV in the hidden charm sector. Also new resonances are predicted, some of them with exotic quantum numbers.

hep-ph↗

arXiv2008

The s-wave pion-nucleus optical potential

We calculate the s-wave part of the pion-nucleus optical potential using a unitarized chiral approach that has been previously used to simultaneously describe pionic hydrogen and deuterium data as well as low energy pi N scattering in the vacuum. This energy dependent model allows for additional isoscalar parts in the potential from multiple rescattering. We consider Pauli blocking and pion polarization in an asymmetric nuclear matter environment. Also, higher order corrections of the pi N amplitude are included. The model can accommodate the repulsion required by phenomenological fits, though the theoretical uncertainties are bigger than previously thought. At the same time, we also find an enhancement of the isovector part compatible with empirical determinations.

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