arXiv subjects

E. Oset

Publications and source records attributed to E. Oset.

At least 181 records · Page 10Linked to original sources

arXiv2013

The width of the omega meson in the nuclear medium

We evaluate the width of the $ω$ meson in nuclear matter. We consider the free decay mode of the $ω$ into three pions, which is dominated by $ρπ$ decay, and replace the $ρ$ and $π$ propagators by their medium modified ones. We also take into account the quasielastic and inelastic processes induced by a vector-baryon interaction dominated by vector meson exchange, as well as the contributions coming from the $ω\to K \bar K$ mechanism with medium modified $K$, $\bar K$ propagators. We obtain a substantial increase of the $ω$ width in the medium, reaching a value of $129 \pm 10$ MeV at normal nuclear matter density for an $ω$ at rest, which comes mainly from $ωN \to ππN, ωN N \to πNN$ processes associated to the dominant $ω\to ρπ$ decay mode. The value of the width increases moderately with momentum, reaching values of around 200 MeV at 600 MeV/c.

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arXiv2013

A study of $ηK \bar K$ and $η' K \bar K$ with the fixed center approximation to Faddeev equations

In the present work we investigate the three-body systems of $ηK \bar K$ and $η' K \bar K$, by taking the fixed center approximation to Faddeev equations. We find a clear and stable resonance structure around 1490 MeV in the squared $ηK \bar K$ scattering amplitude, which is not sensitive to the renormalization parameters. Conversely, we get only an enhancement effect of the threshold in the $η' K \bar K$ amplitude that indicates the difficulty to bind the $η' K \bar K$ system as a consequence of a weaker $η' K$ interaction than the $ηK$ one. We associate the $ηK \bar K$ state found to the $η(1475)$.

hep-ph↗

arXiv2013

Reanalysis of the $e^+ e^- \to (D^* \bar D^*)^{\pm} π^{\mp}$ reaction and the claim for the $Z_c (4025)$ resonance

In this paper we study the reaction $e^+ e^- \to (D^* \bar D^*)^{\pm} π^{\mp}$ in which the BESIII collaboration has claimed the existence of a $1^+$ resonance, named $Z_c(4025)$, in the $D^*\bar D^*$ invariant mass spectrum with a mass around 4026 MeV and width close to 26 MeV. We determine the $D^*\bar D^*$ invariant mass distribution and find that although the explanation considered by the BESIII collaboration is plausible, there are others which are equally possible, like a $2^+$ resonance or a bound state. Even more, we find that the data can be explained without the existence of a resonance/bound state. In view of the different possible interpretations found for the BESIII data, we try to devise a strategy which could help in identifying the origin of the signal reported by the BESIII collaboration. For this, we study the dependence of the $D^*\bar D^*$ spectrum considering the different options as a function of the total center of mass energy. We arrive to the conclusion that increasing the center of mass energy from 4.26 GeV to 4.6 GeV can be useful to distinguish between a resonance, a bound state or just a pure background as being responsible for the signal found. This information should be useful for future experiments.

hep-ph↗

arXiv2013

Strategies for an accurate determination of the X(3872) energy from QCD lattice simulations

We develop a method to determine accurately the binding energy of the X(3872) from lattice data for the $D \bar D^*$ interaction. We show that, because of the small difference between the neutral and charged components of the X(3872), it is necessary to differentiate them in the energy levels of the lattice spectrum if one wishes to have a precise determination of the the binding energy of the X(3872). The analysis of the data requires the use of coupled channels. Depending on the number of levels available and the size of the box we determine the precision needed in the lattice energies to finally obtain a desired accuracy in the binding energy.

hep-lat↗

arXiv2013

Three-body hadron systems with strangeness

Recently, many efforts are being put in studying three-hadron systems made of mesons and baryons and interesting results are being found. In this talk, I summarize the main features of the formalism used to study such three hadron systems with strangeness $S=-1,0$ within a framework built on the basis of unitary chiral theories and solution of the Faddeev equations. In particular, I present the results obtained for the $π\bar{K}N$, $K\bar{K}N$ and $KK\bar{K}$ systems and their respective coupled channels. In the first case, we find four $Σ$'s and two $Λ$'s with spin-parity $J^P=1/2^+$, in the 1500-1800 MeV region, as two meson-one baryon s-wave resonances. In the second case, a $1/2^+$ $N^*$ around 1900 MeV is found. For the last one a kaon close to 1420 MeV is formed, which can be identified with K(1460).

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arXiv2013

Study of the $\bar K N$ system and coupled channels in a finite volume

We investigate the $\bar KN$ and coupled channels system in a finite volume and study the properties of the $Λ(1405)$ resonance. We calculate the energy levels in a finite volume and solve the inverse problem of determining the resonance position in the infinite volume. We devise the best strategy of analysis to obtain the two poles of the $Λ(1405)$ in the infinite volume case, with sufficient precision to distinguish them.

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arXiv2013

$N^*(1920)(1/2^+)$ state in the $NK\bar{K}$ system

We study the three body $N \bar{K} K$ system 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. Our results suggest that a $N\bar{K}K$ hadron state, with spin-parity $J^P=1/2^+$, and mass around 1920 MeV, can be formed.

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arXiv2013

On the isospin 0 and 1 resonances from $πΣ$ photoproduction data

Recently we presented a successful strategy to extract the position of the two $Λ(1405)$ poles from experimental photoproduction data on the $γp \to K^+ π^0 Σ^0 $ reaction at Jefferson Lab. Following a similar strategy, we extend the previous method to incorporate also the isospin 1 component which allows us to consider in addition the experimental data on $γp \to K^+ π^\pm Σ^\mp$. The idea is based on considering a production mechanism as model independent as possible and implementing the final state interaction of the final meson-baryon pair based on small modifications of the unitary chiral perturbation theory amplitudes. Good fits to the data are obtained with this procedure, by means of which we can also predict the cross sections for the $K^- p \to \bar K N$, $πΣ$, $πΛ$ reactions for the different charge channels. Besides the two poles found for the $Λ(1405)$ resonance, we discuss the possible existence of an isospin 1 resonance in the vicinity of the $\bar K N$ threshold.

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arXiv2013

Searching for a hidden charm $h_1$ state in the $X(4660) \to ηh_1$ and $X(4660) \to ηD^* \bar D^*$ decays

We explore the possibility of experimentally detecting a predicted $h_1 ~[I^G(J^{PC})=0^-(1^{+-})]$ state of hidden charm made out from the $D^* \bar D^*$ interaction. The method consists in measuring the decay of X(4660) into $ηD^* \bar D^*$, determining the binding energy with respect to the $D^* \bar D^*$ threshold from the shape of the $D^* \bar D^*$ invariant mass distribution. A complementary method consists in looking at the inclusive $X(4660) \to ηX$ decay, searching for a peak in the $X$ invariant mass distribution given by the missing X(4660), $η$ mass. We make calculations to determine the partial decay width of $X(4660) \to ηh_1$ from the measured $X(4660) \to ηD^* \bar D^*$ distribution. This estimation should serve in an experiment to foresee the possibility of detecting the $h_1$ state on top of the background of inclusive events.

hep-ph↗

arXiv2013

The role of $f_0(1710)$ in the $ϕω$ threshold peak of $J/Ψ\to γϕω$

We study the process $J/Ψ\to γϕω$, measured by the BES experiment, where a neat peak close to the $ϕω$ threshold is observed and is associated to a scalar meson resonance around 1800 MeV. We make the observation that a scalar resonance coupling to $ϕω$ unavoidably couples strongly to $K \bar K$, but no trace of a peak is seen in the $K \bar K$ spectrum of the $J/Ψ\to γK \bar K$ at this energy. This serves us to rule out the interpretation of the observed peak as a signal of a new resonance. After this is done, a thorough study is performed on the production of a pair of vector mesons and how its interaction leads necessarily to a peak in the $J/Ψ\to γϕω$ reaction close to the $ϕω$ threshold, due to the dynamical generation of the $f_0(1710)$ resonance by the vector-vector interaction. We then show that both the shape obtained for the $ϕω$ mass distribution, as well as the strength are naturally reproduced by this mechanism. The work also explains why the $ϕω$ peak is observed in the BES experiment and not in other reactions, like $B^\pm\to K^\pm ϕω$ of Belle.

hep-ph↗

arXiv2013

Exploring the $D^*ρ$ system within QCD sum rules

We present a study of the $D^*ρ$ system made by using the method of QCD sum rules to determine the mass of possible resonances generated in the same system. Using isospin and spin projectors, we investigate the different configurations and obtain evidences for three $D^*$ mesons with isospin $I=1/2$, spin S=0, 1, 2 and with masses $2500\pm 67$ MeV, $2523\pm60$ MeV, and $2439\pm119$ MeV, respectively. The last state can be associated with $D^*_2(2460)$ (spin 2) listed by the Particle Data Group, while one of the first two might be related to $D^*(2640)$, with unknown spin-parity. In the case of $I=3/2$ we also find evidences of three states with spin 0, 1 and 2, respectively, with masses $2467\pm82$ MeV, $2420\pm128$ MeV, and $2550\pm56$ MeV. The results for the sector $I=1/2$ and S=0, 1, 2, are intriguingly similar to a previous study of the $D^*ρ$ system based on effective field theories, supporting in this way a molecular picture for the resonances $D^*(2640)$ and $D^*_2(2460)$, while the results for $I=3/2$ hint towards the existence of exotic mesons since a multiquark configuration is required to get the quantum numbers of the states found.

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arXiv2013

Signature of an $h_1$ state in the $J/ψ\to ηh_1 \to ηK^{0}\bar{K}^{0}$ decay

The BES data on the $J/ψ\to ηK^{*0}\bar{K}^{*0}$ reaction show a clear enhancement in the $K^{*0}\bar{K}^{*0}$ mass distribution close to the threshold of this channel. Such an enhancement is usually a signature of a L=0 resonance around threshold, which in this case would correspond to an $h_1$ state with quantum numbers $I^G(J^{PC})=0^-(1^{+-})$. A state around $1800\ \text{MeV}$ results from the interaction of the $K^* \bar{K}^*$ using the local hidden gauge approach. We show that the peak observed in $J/ψ\to ηK^{*0}\bar{K}^{*0}$ naturally comes from the creation of this $h_1$ state with mass and width around $1830\ \text{MeV}$ and $110\ \text{MeV}$, respectively. A second analysis, model independent, corroborates the first result, confirming the relationship of the enhancement in the invariant mass spectrum with the $h_1$ resonance.

hep-ph↗

arXiv2013

Hidden beauty molecules within the local hidden gauge approach and heavy quark spin symmetry

Using a coupled channel unitary approach, combining the heavy quark spin symmetry and the dynamics of the local hidden gauge, we investigate the meson-meson interaction with hidden beauty and obtain several new states. Both I=0 and I=1 states are analyzed and it is shown that in the I=1 sector, the interactions are too weak to create any bound states within our framework. In total, we predict with confidence the existence of 6 bound states, and weakly bound 6 more possible states. The existence of these weakly bound states depend on the influence of the coupled channel effects.

hep-ph↗

arXiv2013

Hidden beauty baryon states in the local hidden gauge approach with heavy quark spin symmetry

Using a coupled channel unitary approach, combining the heavy quark spin symmetry and the dynamics of the local hidden gauge, we investigate the meson-baryon interaction with hidden beauty and obtain several new states of $N^*$ around 11 GeV. We consider the basis of states $η_b N$, $ΥN$, $B Λ_b$, $B Σ_b$, $B^* Λ_b$, $B^* Σ_b$, $B^* Σ_b^*$ and find four basic bound states which correspond to $B Σ_b$, $B Σ_b^*$, $B^* Σ_b$ and $B^* Σ_b^*$, decaying mostly into $η_b N$ and $ΥN$ and with a binding energy about 50-130 MeV with respect to the thresholds of the corresponding channel. All of them have isospin $I=1/2$, and there are no bound states or resonances in $I=3/2$. The $B Σ_b$ state appears in $J=1/2$, the $B Σ_b^*$ in $J=3/2$, the $B^* Σ_b$ appears nearly degenerate in $J=1/2, ~3/2$ and the $B^* Σ_b^*$ appears nearly degenerate in $J=1/2, ~3/2, ~5/2$. These states have a width from $6 \sim 45 \mev$ except for the one in $J=5/2$ which has zero width since it cannot decay into any of the states of the basis chosen.

hep-ph↗

arXiv2013

Combining heavy quark spin and local hidden gauge symmetries in the dynamical generation of hidden charm baryons

We present a coupled channel unitary approach to obtain states dynamically generated from the meson baryon interaction with hidden charm, using constraints of heavy quark spin symmetry. We use as basis of states, $\bar D B$, $\bar D^* B$ states, with $B$ baryon charmed states belonging to the 20 representations of SU(4) with $J^P=1/2^+,~3/2^+$. In addition we also include the $η_c N$ and $J/ψN$ states. The inclusion of these coupled channels is demanded by heavy quark spin symmetry, since in the large $m_Q$ limit the $D$ and $D^*$ states are degenerate and are obtained from each other by means of a spin rotation, under which QCD is invariant. The novelty in the work is that we use dynamics from the extrapolation of the local hidden gauge model to SU(4) and we show that this dynamics fully respects the constraints of heavy quark spin symmetry. With the full space of states demanded by the heavy quark spin symmetry and the dynamics of the local hidden gauge we look for states dynamically generated and find four basic states which are bound, corresponding to $\bar D Σ_c$, $\bar D Σ_c^*$, $\bar D^* Σ_c$ and $\bar D^* Σ_c^*$, decaying mostly into $η_c N$ and $J/ψN$. All the states appear in isospin $I=1/2$ and we find no bound states or resonances in $I=3/2$. The $\bar D Σ_c$ state appears in $J=1/2$, the $\bar D Σ_c^*$ in $J=3/2$, the $\bar D^* Σ_c$ appears nearly degenerate in $J=1/2, ~3/2$ and the $\bar D^* Σ_c^*$ appears nearly degenerate in $J=1/2, ~3/2, ~5/2$, with the peculiarity that in $J=5/2$ the state has zero width in the space of states chosen. All the states are bound with about 50 MeV with respect to the corresponding $\bar D B$ thresholds and the width, except for the $J=5/2$ state, is also of the same order of magnitude.

hep-ph↗

arXiv2013

A case in favor of the $N^*(1700)(3/2^-)$

Using an interaction extracted from the local hidden gauge Lagrangians, which brings together vector and pseudoscalar mesons, and the coupled channels $ρN$ (s-wave), $πN$ (d-wave), $πΔ$ (s-wave) and $πΔ$ (d-wave), we look in the region of $\sqrt s =1400-1850$ MeV and we find two resonances dynamically generated by the interaction of these channels, which are naturally associated to the $N^*(1520) (3/2^-)$ and $N^*(1700) (3/2^-)$. The $N^*(1700) (3/2^-)$ appears neatly as a pole in the complex plane. The free parameters of the theory are chosen to fit the $πN$ (d-wave) data. Both the real and imaginary parts of the $πN$ amplitude vanish in our approach in the vicinity of this resonance, similarly to what happens in experimental determinations, what makes this signal very weak in this channel. This feature could explain why this resonance does not show up in some experimental analyses, but the situation is analogous to that of the $f_0(980)$ resonance, the second scalar meson after the $σ(f_0(500))$ in the $ππ$(d-wave) amplitude. The unitary coupled channel approach followed here, in connection with the experimental data, leads automatically to a pole in the 1700 MeV region and makes this second $3/2^-$ resonance unavoidable.

hep-ph↗

arXiv2013

Lambda(1405) poles obtained from pi0-Sigma0 photoproduction data

We present a strategy to extract the position of the two $Λ(1405)$ poles from experimental photoproduction data measured recently at different energies in the $γp \to K^+ π^0 Σ^0 $ reaction at Jefferson Lab. By means of a chiral dynamics motivated potential but with free parameters, we solve the Bethe Salpeter equation in the coupled channels $\bar K N$ and $πΣ$ in isospin I=0 and parameterize the amplitude for the photonuclear reaction in terms of a linear combination of the $πΣ\to πΣ$ and $\bar K N \to πΣ$ scattering amplitudes in I=0, with a different linear combination for each energy. Good fits to the data are obtained with some sets of parameters, by means of which one can also predict the cross section for the $K^- p \to π^0 Σ^0 $ reaction. These later results help us decide among the possible solutions. The result is that the different solutions lead to two poles similar to those found in the chiral unitary approach. With the best result we find the two $Λ(1405)$ poles at $1385-68i\mev$and $1419-22i\mev$.

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arXiv2013

The pion-pion Interaction in the rho Channel in Finite Volume

The aim of this paper is to investigate an efficient strategy that allows to obtain pi-pi phase shifts and rho meson properties from QCD lattice data with high precision. For this purpose we evaluate the levels of the pi-pi system in the rho channel in finite volume using chiral unitary theory. We investigate the dependence on the pi mass and compare with other approaches which use QCD lattice calculations and effective theories. We also illustrate the errors induced by using the conventional Luscher approach instead of a more accurate one recently developed that takes into account exactly the relativistic two meson propagators. Finally we make use of this latter approach to solve the inverse problem, getting pi-pi phase shifts from "synthetic" lattice data, providing an optimal strategy and showing which accuracy is needed in these data to obtain the $ρ$ properties with a desired accuracy.

hep-lat↗