arXiv subjects

A. Martínez Torres

Publications and source records attributed to A. Martínez Torres.

At least 37 records · Page 2Linked to original sources

arXiv2016

Looking for bound states and resonances in the $η^\prime K\bar K$ system

Motivated by the continuous experimental investigations of $X(1835)$ in three-body decay channels like $η^\prime π^+ π^-$, we investigate the $η^\prime K \bar K$ system with the aim of searching for bound states and/or resonances when the dynamics involved in the $K\bar K$ subsystem can form the resonances: $f_0(980)$ in isospin 0 or $a_0(980)$ in isospin 1. For this, we solve the Faddeev equations for the three-body system. The input two-body $t$-matrices are obtained by solving Bethe-Salpeter equations in a coupled channel formalism. As a result, no signal of a three-body bound state or resonance is found.

hep-ph↗

arXiv2016

A QCD sum rule calculation of the $X^\pm(5568) \to B_{s}^0π^\pm$ decay width

To understand the nature of the $X(5568)$, recently observed in the mass spectrum of the $B_{s}^0π^\pm$ system by the D0 Collaboration, we have investigated, in a previous work, a scalar tetraquark (diquak-antidiquark) structure for it, within the two-point QCD sum rules method. The result found for its mass agrees well with the experimental value. Encouraged by this finding we now extend our calculations to obtain the decay width of $X(5568)$ to $B_{s}^0π^\pm$ using the three-point QCD sum rule. We obtain a value of $(20.4\pm8.7)\MeV$, which, on comparing with the experimental value of $21.9\pm6.4 (\mbox{sta})^{+5.0}_{-2.5}(\mbox{syst}) \MeV/c^2$, reinforces the scalar four quark nature of $X(5568)$.

hep-ph↗

arXiv2015

Reanalysis of lattice QCD spectra leading to the $D_{s0}^(2317)$ and $D_{s1}^(2460)$

We perform a reanalysis of the energy levels obtained in a recent lattice QCD simulation, from where the existence of bound states of $KD$ and $KD^*$ are induced and identified with the narrow $D_{s0}^*(2317)$ and $D_{s1}^*(2460)$ resonances. The reanalysis is done in terms of an auxiliary potential, employing a single-channel basis $KD^{(*)}$, and a two-channel basis $KD^{(*)}, ηD_s^{(*)}$. By means of an extended Lüscher method we determine poles of the continuum $t$-matrix, bound by about 40 MeV with respect to the $KD$ and $KD^*$ thresholds, which we identify with the $D_{s0}^*(2317)$ and $D_{s1}^*(2460)$ resonances. Using a sum rule that reformulates Weinberg compositeness condition we can determine that the state $D_{s0}^*(2317)$ contains a $KD$ component in an amount of about 70%, while the state $D_{s1}^*(2460)$ contains a similar amount of $KD^*$. We argue that the present lattice simulation results do not still allow us to determine which are the missing channels in the bound state wave functions and we discuss the necessary information that can lead to answer this question.

hep-lat↗

arXiv2013

Role of vector and pseudoscalar mesons in understanding $1/2^-$ $N^*$ and $Δ$ resonances

A study of nonstrange meson-baryon systems has been made with the idea of understanding the properties of the low-lying $1/2^-$ $N^*$ and $Δ$ resonances. The coupled channels are built by considering the pseudoscalar and vector mesons together with the octet baryons. The formalism is based on obtaining the interactions from the lowest order chiral Lagrangian when dealing with pseudoscalar mesons and relying on the hidden local symmetry in case of the vector mesons. The transition between the two systems is obtained by replacing the photon by a vector meson in the Kroll-Ruderman theorem for the photoproduction of pseudoscalar mesons. The subtraction constants, required to calculate the loop-function in the scattering equations, are constrained by fitting the available experimental data on some of the reactions with pseudoscalar meson-baryon final states. As a consequence, we find resonances which can be related to $N^*(1535)$, $N^*(1650)$ (with a double pole structure), $N^*(1895)$ and $Δ(1620)$. We conclude that these resonances can be, at least partly, interpreted as dynamically generated resonances and that the vector mesons play an important role in determining the dynamical origin of the low-lying $N^*$ and $Δ$ states.

nucl-th↗

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

$N^*$'s and $Δ$'s generated in vector, pseudoscalar meson-baryon systems

We have recently studied coupled channel interactions of vector and pseudoscalar mesons with octet baryons having total strangeness null and spin-parity $1/2^-$. We, thus, considered $πN$, $ηN$, $K Λ$, $K Σ$, $ρN$, $ωN$, $ϕN$, $K^* Λ$, and $K^*Σ$ with total isospin 1/2 and 3/2. The interactions between pseudoscalar mesons and baryons are obtained by using the Weinberg-Tomozawa theorem. For the case of vector mesons, we calculate $s$-, $t$-, $u$-exchange diagrams and a contact term. The subtraction constants, required to calculate the loop-function in the scattering equations, are constrained by fitting the available experimental data on some of the reactions with pseudoscalar meson-baryon final states. We end up finding resonances which can be related to $N^*(1535)$, $N^*(1650)$ (with a double pole structure), $N^*(1895)$ and $Δ(1620)$. We conclude that these resonances can be, at least partly, interpreted as dynamically generated resonances and that the vector mesons play an important role in determining the dynamical origin of the low-lying $N^*$ and $Δ$ states.

nucl-th↗

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).

nucl-th↗

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.

nucl-th↗

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.

nucl-th↗

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.

nucl-th↗

arXiv2013

Predicting the existence of a 2.9 GeV $Df_0(980)$ molecular state

A $D$-like meson resonance with mass around 2.9 GeV has been found in the $DK\bar K$ system using two independent and different model calculations based on: (1) QCD sum rules and (2) solution of Fadeev equations with input interactions obtained from effective field theories built by considering both chiral and heavy quark symmetries. The QCD sum rules have been used to study the $D_{s^*0}(2317) \bar{K}$ and $D f_0(980)$ molecular currents. A resonance of mass 2.926 GeV is found with the $D f_0(980)$ current. Although a state in the $D_{s^*0}(2317) \bar{K}$ current is also obtained, with mass around 2.9 GeV, the coupling of this state is found to be two times weaker than the one formed in $D f_0(980)$. On the other hand, few-body equations are solved for the $D K \bar{K}$ system and its coupled channels with the input $t$-matrices obtained by solving Bethe-Salpeter equations for the $D K$, $D\bar{K}$ and $K \bar{K}$ subsystems. In this study a $D$-like meson with mass 2.890 GeV and full width $\sim$ 55 MeV is found to get dynamically generated when $D K \bar{K}$ gets reorganized as $D f_0(980)$. However, no clear signal appears for the $D_{s^*0}(2317) \bar{K}$ configuration. The striking similarity between the results obtained in the two different models indicates strongly towards the existence of a $D f_0 (980)$ molecule with mass nearly 2.9 GeV.

hep-ph↗

arXiv2013

Magnetic moments of the low-lying {1/2}^- octet baryon resonances

The magnetic moments of the negative parity octet resonances with spin {1/2}: $N^*$(1535), $N^*$(1650), $Σ^*$(1620), and $Ξ^*$(1690) have been calculated within the framework of the chiral constituent quark model. In this approach, the presence of the polarized $q\bar{q}$ pairs (or the meson cloud, in other words) is considered by using the Lagrangian for Goldstone boson emission from the constituent quarks. Further, the explicit contributions coming from the spin and orbital angular momentum, including the effects of the configurations mixing between the states with different spins, are obtained. The motivation for these calculations comes from the recent interest in experimental measurement of the magnetic moment of the ${S_{11}(1535)}$ resonance and of similar calculations being done within lattice quantum chromodynamics approaches. Our results can be compared with those expected to come from these sources.

hep-ph↗

arXiv2012

Strategy to find the two $Λ(1405)$ states from lattice QCD simulations

Theoretical studies within the chiral unitary approach, and recent experiments, have provided evidence of the existence of two isoscalar states in the region of the $Λ(1405)$. In this paper we use the same chiral approach to generate energy levels in a finite box. In a second step, assuming that these energies correspond to lattice QCD results, we devise the best strategy of analysis to obtain the two states in the infinite volume case, with sufficient precision to distinguish them. We find out that using energy levels obtained with asymmetric boxes and/or with a moving frame, with reasonable errors in the energies, one has a successful scheme to get the two $Λ(1405)$ poles.

hep-lat↗

arXiv2012

Magnetic moments of the low-lying $J^P=\,1/2^-$, $3/2^-$ $Λ$ resonances within the framework of the chiral quark model

The magnetic moments of the low-lying spin-parity $J^P=$ $1/2^-$, $3/2^-$ $Λ$ resonances, like, for example, $Λ(1405)$ $1/2^-$, $Λ(1520)$ $3/2^-$, as well as their transition magnetic moments, are calculated using the chiral quark model. The results found are compared with those obtained from the nonrelativistic quark model and those of unitary chiral theories, where some of these states are generated through the dynamics of two hadron coupled channels and their unitarization.

nucl-th↗

arXiv2012

Negative parity $Λ$ and $Σ$ resonances coupled to pseudoscalar and vector mesons

An exploration of the dynamically generated $Λ$ and $Σ$ resonances has been made in the vector meson-baryon (VB) systems coupled to pseudoscalar meson-baryon (PB) channels. The VB interactions are obtained from the Lagrangians written within the hidden local symmetry which, in addition to Yukawa-type vector-baryon-baryon (VBB) vertices, naturally gives rise to a contact interaction. Using the VBB vertices, we calculate the $t$-, $s$- and $u$-channel diagrams considering the octet baryon exchange in the latter two cases. For the PB channels we rely on the the Weingberg-Tomozawa interactions and calculate the PB $\leftrightarrow$ VB transition amplitudes extending the Kroll-Ruderman theorem by replacing the photon by the vector mesons. In addition to the low-lying $Λ(1405)$, $Λ(1670)$ found in previous works, we find resonances which coincide well with: $Λ(2000)$, $Σ(1750) S_{11}$, $Σ(1940) D_{13}$, $Σ(2000) S_{11}$ and predict three $Λ^*$'s with $J^π= 3/2^-$ and masses: $1754 - i2$ MeV, $1862 - i33$ MeV, $2139 - i14$ MeV together with a broad $1/2^-$ $Σ^*$ with mass $\sim$ 1430 MeV. We find that most of these next-to-low-lying states couple weakly with the pseudoscalar mesons, which implies that it is important to study the reactions with VB final states in order to obtain a reliable information on the properties of such resonances.

nucl-th↗

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

Vector- and Pseudoscalar-baryon coupled channel systems

In this manuscript, I will report the details of our recent work on the vector meson-baryon (VB) interaction, which we studied with the motivation of finding dynamical generation of resonances in the corresponding systems. We started our study by building a formalism based on the hidden local symmetry and calculating the leading order contributions to the scattering equations by summing the diagrams with: (a) a vector meson exchange in the t-channel (b) an octet baryon exchange in the s-, u-channels and (c) a contact interaction arising from the part of the vector meson-baryon Lagrangian which is related to the anomalous magnetic moment of the baryons. We find the contribution from all these sources, except the s-channel, to be important. The amplitudes obtained by solving the coupled channel Bethe-Salpeter equations for the systems with total strangeness zero, show generation of one isospin 3/2, spin 1/2 resonance and three isospin 1/2 resonances: two with spin 3/2 and one with spin 1/2. We identify these resonances with $Δ$ (1900) $S_{31}$, $N^*$(2080) $D_{13}$, $N^*$(1700) $D_{13}$, and $N^*$(2090) $S_{11}$, respectively. We have further extended our study by including pseudoscalar meson-baryon (PB) as the coupled channels of VB systems. For this, we obtain the PB $\rightarrow$ VB amplitudes by using the Kroll-Ruddermann term where, considering the vector meson dominance phenomena, the photon is replaced by a vector meson. The calculations done within this formalism reveal a very strong coupling of the VB channels to the low-lying resonances like $Λ$(1405) and $Λ$(1670), which can have important implications on certain reactions producing them. In addition to this, we find that the effect of coupling the higher mass states to the lighter channels is not restricted to increasing the width of those states, it can be far more strong.

nucl-th↗