arXiv subjects

A. Martínez Torres

Publications and source records attributed to A. Martínez Torres.

At least 55 records · Page 3Linked to original sources

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.

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arXiv2011

Coupling vector and pseudoscalar mesons to study baryon resonances

A study of meson-baryon systems with total strangeness -1 is made within a framework based on the chiral and hidden local symmetries. These systems consist of octet baryons, pseudoscalar and vector mesons. The pseudoscalar meson-baryon (PB) dynamics has been earlier found determinant for the existence of some strangeness -1 resonances, for example, $Λ(1405)$, $Λ(1670)$, etc. The motivation of the present work is to study the effect of coupling the closed vector meson-baryon (VB) channels to these resonances. To do this, we obtain the $PB \rightarrow PB$ and $VB \rightarrow VB$ amplitudes from the t-channel diagrams and the $PB \leftrightarrow VB$ amplitudes are calculated 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 $Λ(1405)$ and $Λ(1670)$. In the isospin 1 case, we find an evidence for a double pole structure of the $Σ(1480)$ which, like the isospin 0 resonances, is also found to couple strongly to the VB channels. The strong coupling of these low-lying resonances to the VB channels can have important implications on certain reactions producing them.

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arXiv2011

Theoretical support for the $π(1300)$ and the recently claimed $f_0(1790)$ as molecular resonances

A study of three-pseudoscalar $πK \bar{K}$ and $ππη$ coupled system is made by solving the Faddeev equations within an approach based on unitary chiral dynamics. A resonance with total isospin one and spin-parity $J^π= 0^-$ is found with mass $\sim$ 1400 MeV when the $K \bar{K}$ system gets reorganized as the $f_0(980)$. This resonance is identified with the $π(1300)$ listed by the Particle Data Group. Further, the two-body amplitude which describes the interaction between a $π$ and the $f_0(980)$ is extracted from the study of the $πK\bar K$ and $ππη$ system and is then employed to study the $f_0(980)ππ$ system. As a result, a scalar resonance is found near 1790 MeV which drives the two $ f_0 (980)π$ systems to resonate as the $π(1300)$ while the invariant mass of the two pions falls in the mass region of the scalar $σ(600)$. These findings support the existence of a new $f_0$ resonance near 1790 MeV, as found by the BES and Crystal Barrel collaborations. Our results show that this $f_0(1790)$ is definitely distinct to $f_0(1710)$, the latter of which seems to possess a glueball structure dominantly.

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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.

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arXiv2011

Theoretical study of the $KK\bar K$ system and dynamical generation of the K(1460) resonance

The $K K\bar K$ system is investigated with a coupled channel approach based on solving the Faddeev equations considering the $KK\bar K$, $Kππ$ and $Kπη$ channels and using as input two-body $t$-matrices that generate dynamically the $f_0(980)$ and $a_0(980)$ resonances. In the present calculation, a quasibound state around 1420 MeV with total isospin $I=1/2$ and spin-parity $J^π=0^-$ is found below the three kaon threshold. This state can be identified with the K(1460) resonance listed by the Particle Data Group. We also study the $KK\bar K$ system in a single channel three-body potential model with two-body effective $KK$ and $K\bar K$ interactions, in which the $K\bar K$ interaction is adjusted to reproduce the properties of the $f_0(980)$ and $a_0(980)$ resonances as $K\bar K$ bound states, obtaining a very similar result to the one found in the Faddeev approach.

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arXiv2011

Plausible explanation of the $Δ_{5/2^{+}}(2000)$ puzzle

From a Faddeev calculation for the $π-(Δρ)_{N_{5/2^{-}}(1675)}$ system we show the plausible existence of three dynamically generated $I(J^{P})=3/2 (5/2^{+})$ baryon states below 2.3 GeV whereas only two resonances, $Δ_{5/2^{+}}(1905)(\ast\ast\ast\ast)$ and $Δ_{5/2^{+}}(2000)(\ast\ast),$ are cataloged in the Particle Data Book Review. Our results give theoretical support to data analyses extracting two distinctive resonances, $Δ_{5/2^{+}}(\sim1740)$ and $Δ_{5/2^{+}}(\sim2200),$ from which the mass of $Δ_{5/2^{+}}(2000)(\ast\ast)$ is estimated. We propose that these two resonances should be cataloged instead of $Δ_{5/2^{+}}(2000).$ This proposal gets further support from the possible assignment of the other baryon states found in the approach in the $I=1/2,3/2$ with $J^{P}=1/2^{+},3/2^{+},5/2^+$ sectors to known baryonic resonances. In particular, $Δ_{1/2^{+}}(1750)(\ast)$ is naturally interpreted as a $πN_{1/2^{-}}(1650)$ bound state.

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arXiv2011

Limits to the Fixed Center Approximation to Faddeev equations: the case of the $ϕ(2170)$

The Fixed Center Approximation to the Faddeev equations (FCA) has been used lately with success in the study of bound systems of three hadrons. It is also important to set the limits of the approach in those problems to prevent proliferation of inaccurate predictions. In this paper we study the case of the $ϕ(2170)$, which has been described by means of Faddeev equations as a resonant state of $ϕ$ and $K \bar{K}$, and show the problems derived from the use of the FCA in its study. At the same time we also expose the limitations of an alternative approach recently proposed.

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arXiv2011

Dynamically generated hadron resonances

As an example of dynamically generated resonances we mention the interaction of vector mesons with baryons within the local hidden gauge formalism which gives rise to a large amount of such states, many of which can be associated to known resonances, while others represent predictions for new resonances. The width of these states coming from decay into pseudoscalar baryon is also addressed. We also mention recent states coming from $Δρπ$ interaction obtained with Faddeev equations.

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arXiv2010

An alternative explanation for the $Θ(1540)$ pentaquark peak

We have studied the $γd \to K^+ K^- n p$ reaction in which the LEPS collaboration found a signal in the $K^+ n$ invariant mass for the claimed $Θ(1540)$ pentaquark peak. Our study reveal that the procedure used at LEPS to reconstruct the $K^+n$ invariant mass generates an artificial strength in the $Θ(1540)$ region and that the LEPS collaboration underestimated the background in that region, such that the signal observed for the $Θ(1540)$ is compatible with a fluctuation of $2σ$ over the calculated background.

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arXiv2010

The $f_0(1370)$, $f_0(1710)$, $f_2(1270)$, $f_2'(1525)$, and $K_2^*(1430)$ as dynamically generated states from vector meson - vector meson interaction

We report on some recent developments in understanding the nature of the low-lying mesonic resonances $f_0(1370)$, $f_0(1710)$, $f_2(1270)$, $f_2'(1525)$, and $K_2^*(1430)$. In particular we show that these five resonances can be dynamically generated from vector meson--vector meson interaction in a coupled-channel unitary approach, which utilizes the phenomenologically very successful hidden-gauge Lagrangians to produce the interaction kernel between two vector mesons, which is then unitarized by the Bethe-Salpeter-equation method. The data on the strong decay branching ratios, total decay widths, and radiative decay widths of these five states, and on related $J/ψ$ decay processes can all be well described by such an approach. We also make predictions, compare them with the results of earlier studies, and highlight observables that if measured can be used to distinguish different pictures of these resonances.

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arXiv2010

$KΛ(1405)$ configuration of the $K\bar{K}N$ system

We study the $KΛ(1405)$ configuration of the $K\bar{K}N$ system by considering $KπΣ$ as a coupled channel. We solve the Faddeev equations for these systems and find confirmation of the existence of a new $N^{*}$ resonance around 1920 MeV with $J^π=1/2^{+}$ predicted in a single-channel potential model and also found in a Faddeev calculation as an $a_{0}(980)N$ state, with the $a_{0}(980)$ generated in the $K\bar{K}$, $πη$ interaction.

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arXiv2010

A novel interpretation of the "$Θ^{+}(1540)$ pentaquark" peak

We use a theoretical model of the $γ~d \to ~K^+ K^- ~n ~p $ reaction adapted to the experiment done at LEPS where a peak was observed and associated to the $Θ^{+}(1540)$ pentaquark. The study shows that the method used in the experiment to associate momenta to the undetected proton and neutron, together with the chosen cuts, necessarily creates an artificial broad peak in the assumed $K^+ n$ invariant mass in the region of the claimed $Θ^{+}(1540)$, such that the remaining strength seen for the experimental peak is compatible with a fluctuation of 2$σ$ significance.

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arXiv2010

Study of the $γd\to K^{+}K^{-}np$ reaction and an alternative explanation for the "$Θ^{+}(1540)$ pentaquark" peak

We present a calculation of the $γd \to K^+ K^- n p $ reaction with the aim of seeing if the experimental peak observed in the $K^+ n$ invariant mass around 1526 MeV, from where evidence for the existence of the $Θ^+$ has been claimed, can be obtained without this resonance as a consequence of the particular dynamics of the process and the cuts applied in the experimental set up. We find that a combination of facts leads indeed to a peak around 1530 MeV for the invariant mass of $K^+ n$ without the need to invoke any new resonance around this energy. This, together with statistical fluctuations that we prove to be large with the statistics of the experiment, is likely to produce the narrower peak observed there.

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arXiv2010

The Y(4260) as a $J/ψK \bar{K}$ system

A study of the $J/ψππ$ and $J/ψK \bar{K}$ systems, treating them as coupled channels, has been made by solving the Faddeev equations, with the purpose of investigating the possibility of generation of the $J^{PC} = 1^{--}$, Y(4260) resonance due to the interaction between these three mesons. In order to do this, we start by solving the Bethe-Salpeter equation for the two pseudoscalar and for the vector-pseudocalar meson systems using the amplitudes obtained from the lowest order chiral Lagrangians as potentials. With the $t$-matrices generated from these potentials, which contain the poles of the $σ$, $f_{0}(980)$ and $a_{0}(980)$ resonances for the pseudoscalar-pseudoscalar system and the pole of the X(3872), alongwith other new charmed resonant states, for the vector-pseudoscalar system, we solve the Faddeev equations. As a result, we get a peak around 4150 MeV with a width $\sim$ 90 MeV when the invariant mass of the two pseudoscalars is close to that of the $f_0 (980)$.

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arXiv2009

Solution to Faddeev equations with two-body experimental amplitudes as input and application to J^P=1/2^+, S=0 baryon resonances

We solve the Faddeev equations for the two meson-one baryon system $ππN$ and coupled channels using the experimental two-body $t$-matrices for the $πN$ interaction as input and unitary chiral dynamics to describe the interaction between the rest of coupled channels. In addition to the $N^*(1710)$ obtained before with the $ππN$ channel, we obtain, for $J^π=1/2^+$ and total isospin of the three-body system $I=1/2$, a resonance peak whose mass is around 2080 MeV and width of 54 MeV, while for $I=3/2$ we find a peak around 2126 MeV and 42 MeV of width. These two resonances can be identified with the $N^* (2100)$ and the $Δ(1910)$, respectively. We obtain another peak in the isospin 1/2 configuration, around 1920 MeV which can be interpreted as a resonance in the $N a_0(980)$ and $N f_0(980)$ systems.

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arXiv2009

Searching for signatures around 1920 MeV of a $N^*$ state of three hadron nature

We provide a series of arguments which support the idea that the peak seen in the $γp \to K^+ Λ$ reaction around 1920 MeV should correspond to the recently predicted state of $J^P=1/2^+$ as a bound state of $K \bar{K}N$ with a mixture of $a_0(980)N$ and $f_0(980)N$ components. At the same time we propose polarization experiments in that reaction as a further test of the prediction, as well as a study of the total cross section for $γp \to K^+ K^- p$ at energies close to threshold and of $d σ/d M_{inv}$ for invariant masses close to the two kaon threshold.

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arXiv2009

Searching for exotic states in the $N πK $ system

We study the $N πK$ system in order to investigate the possibility of existence of strangeness +1 resonance(s). The formalism consists of solving the Faddeev equations with the $N π$, $πK $ and $K N$ $t$-matrices obtained from chiral dynamics. The same formalism, which leads to the finding of several $1/2^+$ resonances in the corresponding three-body $S$ = -1 channels in the 1400-2000 MeV energy region, results into only one broad bump around 1700 MeV with isospin 0. The amplitudes in isospin 1 and 2 configuration do not have any resonant structure.

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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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