arXiv subjects

A. Martinez Torres

Publications and source records attributed to A. Martinez Torres.

At least 19 recordsLinked to original sources

arXiv2026

Enigmatic properties of $Ξ(1620)$ and $Ξ(1690)$

Motivated by a considerable release of data on first two excited states of the doubly strange baryon, $Ξ(1620)$ and $Ξ(1690)$, from different experimental collaborations in recent years, we investigate meson-baryon interactions in a coupled-channel approach. The systems are composed of pseudoscalar and vector mesons and the calculations are done for the total spin 1/2 and isospin 1/2 configuration. The tree-level interactions are deduced from Lagrangians based on chiral and hidden local symmetries. Specifically, we make an attempt to describe (1) data on the $K^-Λ$ femtoscopic correlation function coming from $p\,p$ and $Pb\,Pb$ collisions, and (2) the available data on invariant mass distributions for different systems: $πΞ$, $\bar K Σ$ and $\bar K Λ$. We find that the amplitude which yields the correlation function close to the data results in mass distributions of different meson-baryon systems that are in discordance with the experimental data and vice-versa.

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arXiv2026

Nature of the newly found $Ω(2109)$

We present model calculations to reveal the nature of the newly found $Ω^-(2109)$ by the BESIII Collaboration, and show that the state has a strong correlation with the $\bar K^*(892)Ξ$ system. Our study is based on solving scattering equations in a coupled channel approach, which involves $K^-Ξ^0$, $\bar K^0Ξ^-$, $K^{*-}Ξ^0$, and $\bar K^{*0}Ξ^-$. We obtain the lowest order amplitudes for different spin and isospin cases and find that an isoscalar state with spin-parity $1/2^-$ is generated with precisely the same mass as $Ω^-(2109)$. We do not find any state with total spin 3/2, nor do we find any state in the isovector sector. We determine correlation functions to encourage such an experimental study and confirm the nature of $Ω^-(2109)$.

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arXiv2026

Revealing the nature of double-strangeness pentaquark states via femtoscopic correlation functions

Recent discoveries of exotic hadrons, which cannot be classified within the conventional quark model of $q \bar{q}$ mesons and $qqq$ baryons, strongly imply the existence of dynamically generated hadronic molecules. Some of these hadron-hadron interactions are accompanied by coupled-channel effects, which remain challenging to quantitatively determine. In this work, we demonstrate that femtoscopy provides a sensitive probe of such coupled-channel dynamics. We calculate correlation functions for the double-strangeness pentaquark candidates $P_{css}(4493)$ ($J^P=1/2^-$) and $P_{css}(4633)$ ($J^P=1/2^-$ or $3/2^-$), revealing clear signatures of the attractive interactions that can form bound states. The results are markedly different from those obtained in scenarios that neglect off-diagonal transitions, highlighting the importance of coupled-channel effects for understanding the structure of these hadrons.

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arXiv2025

Correlation functions for $n\,\bar{D}_{s1}(2460)$ and $n\,\bar{D}_{s1}(2536)$

We study the interaction of the $n \bar {D}_{s1}(2460)$ and $n \bar {D}_{s1}(2536)$ systems from the perspective that the $D_{s1}(2460)$ and $D_{s1}(2536)$ states are molecular states of $K D^*$ and $K^*D$, respectively. We use an improved version of the fixed center approximation to the Faddeev equations which fulfills exact elastic unitarity at the threshold of the systems. We predict the existence of resonant states below threshold and also determine the scattering length, effective range and correlation functions of these systems, showing that the results contain important information to test the assumed molecular nature of the two $D_{s1}$ states.

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arXiv2025

Strangeness $+1$ light multiquark baryons

In view of the renewing experimental interest for searching strangeness $+1$ baryons at J-PARC, we study the existence of light baryon resonances with strangeness +1 generated in the $K$-$(N^*/Δ^*)$ system, where $N^*$ represents either $N^*(1535)$/$N^*(1650)$/$N^*(1700)$, and $Δ^*$ corresponds to $Δ(1620)$. The description of the properties of the aforementioned states requires considering the dynamics involved in the coupled pseudoscalar-baryon and vector-baryon systems with strangeness $S=0$ in the s-wave. For the purpose of our current study, we consider the pseudoscalar-baryon (PB) and vector-baryon channels (VB) to which the mentioned $N^*$ and $Δ^*$ resonances couple and solve the Faddeev equations for the coupled channel system $K$-$\text{PB}$, $K$-$\text{VB}$, with all interactions being in the s-wave. Despite some strong attraction present in two of the subsystems, we do not find clear evidence supporting the formation of strangeness +1 states, with spin-parity $J^P=1/2^+$, in the energy region $2000-2200$ MeV. However, the case of spin-parity $J^P=3/2^+$ seems more promising, showing the formation of a resonance with a mass around 2167 MeV, with a width of 90-100 MeV. We suggest that a signal of such a state could be found in processes with final states like $KN$, $K^*(892) N$.

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arXiv2024

Bolstering up the existence of $P_s(2080)$

We present a detailed study of the partial decay widths of a spin-parity resonance $J^P=3/2^-$ $N^*$ with a mass of $\simeq$ 2070 MeV obtained from the coupled channel s wave vector-baryon $ρN$, $ωN$, $ϕN$, $K^*Λ$ and $K^*Σ$ dynamics. This state, which couples strongly to the $K^*Σ$ channel, corresponds to a nucleon with a hidden strange quark content, in analogy to the $P_c$ states discovered by the LHCb collaboration, and we denote it as $P_s(2080)$. A state with such a nature can decay to vector-baryon, pseudoscalar-baryon, and pseudoscalar-baryon resonance channels, involving triangular loops in the latter two cases. As we will show, the partial decay widths to pseudoscalar-baryon resonance channels, like $πN^*(1535)$, $πN^*(1650)$, $KΛ(1405)$, are comparable to those related to ground state baryons in the final state, like $πN$, $ηN$, $KΛ$. In this way, reactions involving such lighter baryon resonances in the final state can be used as an alternative source of information on the properties of a $N^*$ with hidden strangeness.

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arXiv2024

A study of the $ϕN$ correlation function

The femtoscopic $ϕN$ correlation function is studied within a hadronic effective Lagrangian approach with coupled channels, based on hidden local symmetry. The results are compared with the data recently reported by the ALICE collaboration. We find that the correlation function has very different features for the $ϕN$ system in the spin 1/2 and 3/2 configurations, with the spin-averaged combination matching well with the experimental data. A strong attraction, leading to the formation of a $ϕN$ bound state or a very prominent cusp is found in the spin 3/2 case. The correlation function for spin 1/2, on the other hand, is strongly impacted by the negative parity $N^*(1895)$ nucleon resonance.

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arXiv2024

Can femtoscopic correlation function shed light on the nature of the lightest, charm, axial mesons?

We present a coupled channel treatment of meson-meson dynamics, for systems with spin-parity $1^+$, and determine the corresponding amplitudes by solving the Bethe-Salpeter equations, which lead to the generation of two axial resonances when mesons are considered as the degrees of freedom in the model. One of them is narrow and has properties in good agreement with those of $D_1(2420)$. The other pole is wider, but its real and imaginary parts do not match well with the mass and width of $D_1(2430)$. The situation improves when a bare quark-model state is included, indicating that the dynamics at the quark level as well as among hadrons can describe the two states simultaneously. Further, we discuss that there exists a divergence in the value of the $D^*π$ scattering length determined through data coming from lattice QCD calculations and from heavy ion collisions. Such different values can be accommodated in the model by making small changes in the parameters while producing two poles having properties compatible with the two lightest $D_1$ states. With these results, we proceed to calculate the correlation function for the $D^{*+(0)}π^{0(+)}$ system for different sizes of the source. We discuss which scenarios can be useful to shed some light on the issue.

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arXiv2024

Intriguing aspects of light baryon resonances

We discuss that some light baryon resonances exhibit properties which cannot be described when attributing a three-valence quark structure to them. Besides pointing out the hadron resonances which clearly require description beyond the quark model, we focus on the third $s_{11},~ N^*$ state and its decay to final states consisting of the lightest hyperon resonances which have a partial width comparable to that for the decay to $πN$. Such properties of the mentioned nucleon resonance get manifested in the cross sections and other observables related to processes producing the lightest hyperon resonances. We show that all these findings arise from the strong association of the baryon resonances to the dynamics among the ground-state hadrons.

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arXiv2024

The properties of $ϕ(2170)$ and its three-body nature

We summarize the results we obtained for the partial decay widths of $ϕ(2170)$ into two-body final states formed by a $\bar K$ and a Kaonic resonance, like $K(1460)$, $K_1(1270)$, as well as to final states constituted by a $ϕ$ and an $η/η^\prime$ mesons. The results obtained are compared with the values extracted from experimental data on the corresponding branching ratios, which were determined by the BESIII collaboration. A reasonable agreement is found, which together with the previous reproduction of the mass, width, and cross section for the process $e^+ e^-\to ϕf_0$ strongly indicates the molecular nature of $ϕ(2170)$ as a $ϕK\bar K$ system.

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arXiv2023

$ϕ(2170)$ decaying to $ϕη$ and $ϕη^\prime$

In this work we calculate the decay widths of $ϕ(2170)$ to $ϕη$ and $ϕη^\prime$ by considering $ϕ(2170)$ as a $ϕK\bar K$ state, with $K\bar K$ clustering as $f_0(980)$. These decay widths have been recently determined by the BESIII, BaBar and Belle collaborations with the aim of unraveling the nature of $ϕ(2170)$. By analyzing the data on the cross sections of the process $e^+e^-\toϕη$, two solutions were found by the BESIII collaboration with the same $χ^2/n.d.f$, mass and width for $ϕ(2170)$. However, different values for $\mathcal{B}^{ϕ(2170)}_{ϕη}Γ^{ϕ(2170)}_{e^+e^-}$ were obtained: $0.24^{+0.12}_{-0.07}$ eV (solution I) and $10.11^{+3.87}_{-3.13}$ eV (solution II). In case of $\mathcal{B}^{ϕ(2170)}_{ϕη^\prime}Γ^{ϕ(2170)}_{e^+e^-}$, a value of $7.1\pm 0.7\pm 0.7$ was determined by the BESIII collaboration from fits to the data on the cross section of $e^+e^-\toϕη^\prime$. The Belle collaboration has also determined $\mathcal{B}^{ϕ(2170)}_{ϕη}Γ^{ϕ(2170)}_{e^+e^-}$ more recently, although the statistical significance related to the signal of $ϕ(2170)$ in the data is low. We calculate the decay widths of $ϕ(2170)$ to $ϕη$ and $ϕη^\prime$, and compare their ratio $Γ^{ϕ(2170)}_{ϕη}/Γ^{ϕ(2170)}_{ϕη^\prime}$ with the one determined by using the above mentioned experimental data. Considering the theoretical and experimental uncertainties, the lower limit of our theoretical result ($\simeq 2.6$) is close to the upper value obtained ($\simeq 2$) by using the solution II of BESIII for $\mathcal{B}^{ϕ(2170)}_{ϕη}Γ^{ϕ(2170)}_{e^+e^-}$, as well as to the upper limit found ($\simeq 2.8$) when considering the solutions III and IV of the Belle collaboration for $\mathcal{B}^{ϕ(2170)}_{ϕη}Γ^{ϕ(2170)}_{e^+e^-}$.

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arXiv2023

$N^*$ states with hidden charm and a three-body nature

In this work we study the formation of $N^*$'s as a consequence of the dynamics involved in the $ND\bar D^*-N\bar D D^*$ system when the $D\bar D^*-\bar D D^*$ subsystem generates $X(3872)$ in isospin 0 and $Z_c(3900)$ in isospin 1. States with isospin $I=1/2$ and mass in the energy region $4400-4600$ MeV are found to arise with spin-parity $J^P=1/2^+$ and $3/2^+$, leading to predictions in this way of the existence of $N^*$ resonances with hidden charm and a three-body nature. We also discuss the possibility of the existence of $Δ_c$ states, i.e., $Δ$'s with hidden charm.

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arXiv2023

Theoretical study of the $γd \to π^0ηd$ reaction

We have done a theoretical study of the $γd \to π^0 ηd$ reaction starting with a realistic model for the $γN \to π^0 ηN$ reaction that reproduces cross sections and polarization observables at low energies and involves the $γN \to Δ(1700)\to ηΔ(1232) \to ηπ^0 N$ process. For the coherent reaction in the deuteron we considered the impulse approximation together with the rescattering of the pions and the $η$ on a different nucleon than the one where they are produced. We found this second mechanism very important since it helps share between two nucleons the otherwise large momentum transfer of the reaction. Other contributions to the $γd\toπ^0ηd$ reaction, involving the $γN\to π^\pmπ^0 N^\prime$ process, followed by the rescattering of the $π^\pm$ with another nucleon to give $η$ and a nucleon, have also been included. We find a natural explanation, tied to the dynamics of our model, for the shift of the $η-d$ mass distribution to lower invariant masses, and of the $π^0-d$ mass distribution to larger invariant masses, compared to a phase space calculation. We also study theoretical uncertainties related to the large momenta of the deuteron wave function involved in the process as well as to the couplings present in the model. Striking differences are found with the experimental angular distribution and further theoretical investigations might be necessary.

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arXiv2022

Exotic properties of N^*(1895) and its impact on photoproduction of light hyperons

In this work, we outline the findings of our recent study of the properties of $N^*(1895)$ and its consequential impacts on the cross sections of the photoproduction of $Λ(1405)$. Further, we discuss the possibility of the existence of an isovector state, with the mass similar to $Λ(1405)$, which we refer to as $Σ(1400)$. With the idea of motivating experimental investigations of $Σ(1400)$, we have studied its photoproduction process and determined the respective cross sections and polarization observables. We have studied also the coupling of $N^*(1895)$ to $KΣ(1400)$ and found that it gives an important contribution to the cross sections near the threshold. In the process, we have determined the branching ratios of the decay of $N^*(1895)$, to the final states involving $Λ(1405)$ and $Σ(1400)$, to be in the range of 6-7 MeV. Our findings can motivate consideration of alternative processes in partial wave analyses of experimental data, when studying the properties of $N^*(1895)$.

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arXiv2022

$D_1(2420)$ and its interactions with a kaon: open charm states with strangeness

In this work we present an attempt to describe the $X_1(2900)$ found by the LHCb collaboration, in the experimental data on the invariant mass spectrum of $ D^-K^+$, as a three-meson molecular state of the $Kρ\bar D$ system. We discuss that the interactions in all the subsystems are attractive in nature, with the $ρ\bar D$ interaction generating $\bar D_1(2420)$ and the $K ρ$ resonating as $K_1(1270)$. We find that the system can form a three-body state but with a mass higher than that of $X_1(2900)$. We investigate the $K ρD$ system too, finding that the three-body dynamics generates an isoscalar state, which can be related to $D_{s1}^*(2860)$, and an exotic isovector state. This latter state has a mass similar to that of the $X_0(2900)$ and $X_1(2900)$ states found by LHCb, but a very small width ($\sim 7.4 \pm 0.9$ MeV) and necessarily requires more than two quarks to describe its properties. We hope that our findings will encourage experimental investigations of the isovector $K ρD$ state. Finally, in the pursuit of finding a description for $X_1(2900)$, we study the $π\bar K^* D^*$ system where $ \bar K^*D^*$ forms $0^+$, $1^+$ and $2^+$ states. We do not find a state which can be associated with $X_1(2900)$.

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arXiv2022

Studying the process $γd \to π^0ηd$

In these proceedings we present our recent results on the study of the process $γd \to π^0 ηd$, where the existence of a dibaryon in the $ηd$ invariant mass distribution has been recently claimed. As we will show, many of the relevant aspects observed in the experiment, as the shift of the $ηd$ and $πd$ invariant mass distributions with respect to phase space can be described with our model, where no dibaryon is formed. Instead, we consider the interaction of the $γ$ with the nucleons forming the deuteron to proceed through $γN \to Δ(1700)\to ηΔ(1232) \to ηπ^0 N$, followed by the rescattering of the $π$ and $η$ with the other nucleon of the deuteron. Theoretical uncertainties related to different parameterizations of the deuteron wave function are investigated

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arXiv2022

Exotic states with triple charm

In this work we investigate the possibility of the formation of states from the dynamics involved in the $D^*D^*D^*$ system by considering that two $D^*$'s generate a $J^P=1^+$ bound state, with isospin 0, which has been predicted in an earlier theoretical work. We solve the Faddeev equations for this system within the fixed center approximation and find the existence of $J^P=0^-$, $1^-$ and $2^-$ states with charm $3$, isospin $1/2$, masses $\sim 6000$ MeV, which are manifestly exotic hadrons, i.e., with a multiquark inner structure.

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arXiv2022

Exotic heavy hadrons with a three-body nature

In this talk we present a summary of our latest results on the investigation of three-body systems with explicit/hidden charm and with explicit/hidden strangeness. To be more concrete, in case of explicit strangeness quantum number, we pay attention on the $K D D $ and $K D\bar D^*$ systems, where, in the former, a charm $+2$, isospin $1/2$ and strangeness $+1$ state is obtained with a mass around 4140 MeV, while in the latter, a $K^*$ state, with hidden charm, and a mass close to 4307 MeV is found. In case of hidden strangeness, the $DK\bar K$ system is studied, while in the hidden charm and no strangeness quantum numbers sector, the $ND\bar D^*$ system is investigated. In the former a meson $D$ with mass around 2900 MeV is found to be generated, while in the latter several $N^*$ and $Δ^*$ states with hidden charm are obtained with masses about $4600$ MeV. All these states constitute predictions of our model and future experimental confirmation of them would be relevant to elucidate the properties of the strong interaction in the presence of heavy quarks.

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