arXiv subjects

L. Roca

Publications and source records attributed to L. Roca.

At least 19 recordsLinked to original sources

arXiv2025

Study of hidden-charm, doubly-strange pentaquarks in $\Lambda_b\to J/\psi \Xi^- K^+$ and $\Xi_b\to J/\psi \Xi^- \pi^+$

Hidden-charm pentaquark states with double strangeness, $P_{css}$, have been predicted within the framework of unitary coupled-channel dynamics. In this work, we theoretically investigate the potential to observe these states in the decays $\Lambda_b\to J/\psi \Xi^-K^+$ and $\Xi_b\to J/\psi\Xi^-\pi^+$. In this framework, these pentaquark configurations couple strongly to the $J/\psi\Xi$ channel, as well as to other vector-baryon channels with the $\bar c c s s n$ flavor structure, making these decay modes promising for their observation through the corresponding invariant-mass distributions. Our analysis begins with the identification of the dominant weak decay mechanisms, followed by hadronization into meson-baryon channels, connected through flavor symmetry. Final-state interactions are then incorporated to dynamically generate the full amplitude, accounting for the formation of the pentaquark states. We compare our results with recent LHCb measurements of the $J/\psi\Xi^-$ mass distribution and find that, given the predicted pentaquark width of about 10 MeV in this channel, the state is too narrow to be resolved with the current experimental resolution, but it would become visible with significantly improved mass precision.

hep-ph↗

arXiv2025

The $D_{s1}(2460) \to D_s \pi^+ \pi^- $ decay from a $D_{s1}$ molecular perspective

We conduct a theoretical study of the $ D_{s1}(2460) \to D_s \pi^+ \pi^- $ decay from the perspective that the $D_{s1}$ is a molecular state, built mostly from the $D^* K$ and $D_s^* \eta$ components. The $D^*$ and $D_s^*$ mesons are allowed to decay into two pseudoscalars, with one of them merging with the other pseudoscalar that forms the $D_{s1}$ state, ultimately leading to the $\pi^+ \pi^- D_s$ final state. This results in a triangle diagram mechanism where all theoretical ingredients are well-known, leading to a free parameter framework. We evaluate the mass distributions of particle pairs and find good agreement with the experimental distributions of a recent LHCb experiment, providing strong support to the molecular picture of the $D_{s1}(2460)$ state. We also discuss the role played by the scalar mesons $f_0(500)$ and $f_0(980)$, at odds with the interpretation of the experimental analysis.

hep-ph↗

arXiv2024

Production of pentaquarks with hidden charm and double strangeness in $\Xi_b$ and $\Omega_b$ decays

Recently, several pentaquark states $P_{css}$, with global flavor $\bar c c s s n$, have been predicted within a theoretical framework based on unitary coupled channels. We study theoretically the feasibility to observe the $P_{css}$ with $I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$ in the decays $\Xi_b^0\to \eta \eta_c \Xi^0$ and $\Omega_b^-\to K^- \eta_c \Xi^0$. Indeed, within the model, the $\eta_c \Xi^0$ channel is the lowest mass pseudoscalar-baryon channel to which this pentaquark state couples, thus we can expect to observe its signal in the $\eta_c \Xi^0$ invariant mass distribution of the mentioned decays. We identify the dominant weak decay processes and then implement the hadronization into the different meson-baryon channels in the final state, linked by flavor symmetry. The dominant meson-baryon final state interaction is then implemented to generate the full amplitude, implicitly accounting for the dynamical emergence of the pentaquark states. We obtain a clear Breit-Wigner-like resonant signal in the spectrum of the $\Omega_b^-$ decay, exceeding that in the $\Xi_b^0$ decay by two to three orders of magnitude. In the case of the latter decay, the resonant state would manifest as a significant dip in the spectrum. We study the feasibility of searching for these $b$-hadron decay modes and analysing their resonant components using the current and future data samples from the LHCb experiment.

hep-ph↗

arXiv2024

Molecular pentaquarks with hidden charm and double strangeness

We analyze theoretically the coupled-channel meson-baryon interaction with global flavor $\bar c c s s n$ and $\bar c c s s s$, where mesons are pseudoscalars or vectors and baryons have $J ^P=1/2^+$ or $3/2^+$. The aim is to explore whether the nonlinear dynamics inherent in the unitarization process within coupled channels can dynamically generate double- and triple-strange pentaquark-type states ($P_{css}$ and $P_{csss}$ respectively), for which there is no experimental evidence to date. We evaluate the s-wave scattering matrix by implementing unitarity in coupled channels, using potential kernels obtained from t-channel vector meson exchange. The required $PPV$ and $VVV$ vertices are obtained from Lagrangians derived through appropriate extensions of the local hidden gauge symmetry approach to the charm sector, while capitalizing on the symmetry of the spin and flavor wave function to evaluate the $BBV$ vertex. We find four different poles in the double strange sector, some of them degenerate in spin. For the triple-strange channel we find the meson-baryon interaction insufficient to generate a bound or resonance state through the unitary coupled-channel dynamics.

hep-ph↗

arXiv2023

Predictions of super-exotic heavy mesons from $K^{}B^{}B^{*}$ interactions

We make a theoretical study of the three-body system composed of ${\bar K^*}{\bar B^*}{\bar B^*}$ to look for possible bound states, which could be associated to mesonic resonances of very exotic nature, containing open strange and double-bottom flavours. The three-body interaction is evaluated by using the fixed center approach to the Faddeev equations where the ${\bar B^*}{\bar B^*}$ is bound forming an $I(J^P)=0(1^+)$ state, as it was found in previous works, and the third particle, the ${\bar B^*}$, of much smaller mass, interacts with the components of the cluster. We obtain bound states for all the channels considered: spin $J=0$, 1 and 2, all of them with isospin $I=1/2$ and negative parity.

hep-ph↗

arXiv2022

Exotic molecular meson states of $B^{()} K^{()}$ nature

We evaluate theoretically the interaction of the open bottom and strange systems $\bar B\bar K$, $\bar B^* \bar K$, $\bar B\bar K^*$ and $\bar B^*\bar K^*$ to look for possible bound states which could correspond to exotic non--quark-antiquark mesons since they would contain at least one $b$ and one $s$ quarks. The s-wave scattering matrix is evaluated implementing unitarity by means of the Bethe-Salpeter equation, with the potential kernels obtained from contact and vector meson exchange mechanisms. The vertices needed are supplied from Lagrangians derived from suitable extensions of the hidden gauge symmetry approach to the bottom sector. We find poles below the respective thresholds for isospin 0 interaction and evaluate the widths of the different obtained states by including the main sources of imaginary part, which are the $B^*\to B\gamma$ decay in the $\bar B^* \bar K$ channels, the $K^*\to K \pi$ in the channels involving a $K^*$, plus the box diagrams with $\bar B\bar K$ and $\bar B^*\bar K$ intermediate states for the $\bar B^*\bar K^*$ channels.

hep-ph↗

arXiv2022

Masses and widths of the exotic molecular $B_{(s)}^{()} B_{(s)}^{()}$ states

We study the interaction of the doubly bottom systems $BB$, $B^* B$, $B_s B$, $B_s^* B$, $B^* B^*$, $B^* B_s$, $B^*B_s^*$, $B_s B_s$, $B_s B_s^*$, $B_s^* B_s^*$ by means of vector meson exchange with Lagrangians from an extension of the local hidden gauge approach. The full s-wave scattering matrix is obtained implementing unitarity in coupled channels by means of the Bethe-Salpeter equation. We find poles below the channel thresholds for the attractively interacting channels $B^* B$ in $I=0$, $B^*_s B-B^*B_s$ in $I=\frac{1}{2}$, $B^* B^*$ in $I=0$, and $B^*_s B^*$ in $I=\frac{1}{2}$, all of them with $J^P=1^+$. For these cases the widths are evaluated identifyng the dominant source of imaginary part. We find binding energies of the order of $10-20$ MeV, and the widths vary much from one system to the other: of the order of 10-100 eV for the $B^* B$ system and $B^*_s B-B^*B_s$, about $6$ MeV for the $B^* B^*$ system and of the order of $0.5$ MeV for the $B^*_s B^*$ system.

hep-ph↗

arXiv2021

Inconsistency of the data on the $K_1(1270) \to \pi K^*_0(1430)$ decay width

We show, using the same Lagrangian for the $K_1(1270) \to \pi K^*_0(1430)$ and $K^*_0(1430) \to K_1(1270) \pi$ decays, that the present PDG data on the partial decay width of $K_1(1270) \to \pi K^*_0(1430)$ implies a width for $K^*_0(1430) \to K_1(1270) \pi$ decay which is about ten times larger than the total $K^*_0(1430)$ width. A discussion on this inconsistency is done, stressing its relationship to the existence of two $K_1(1270)$ states obtained with the chiral unitary theory, which are not considered in the experimental analyses of $K\pi\pi$ data.

hep-ph↗

arXiv2021

Unveiling the $K_1(1270)$ double-pole structure in the $\bar{B}\to J/\psi \rho\bar{K}$ and $\bar{B}\to J/\psi \bar{K}^*\pi$ decays

By looking at the pseudoscalar-vector meson spectra in the $\bar{B}\to J/\psi \rho\bar{K}$ and $\bar{B}\to J/\psi \bar{K}^*\pi$ weak decays, we theoretically investigate the double-pole structure of the $K_1(1270)$ resonance by using the Chiral Unitary approach to account for the final state interactions between the pseudoscalar and vector mesons. The $K_1(1270)$ resonance appears as dynamically generated through these interactions in coupled channels and influence the shape of the invariant mass distributions under consideration. We show how those shapes are affected by the $K_1(1270)$ double-pole structure to confront the results from our model with future experiments that might investigate the $PV$ spectra in these decays.

hep-ph↗

arXiv2020

Scalar resonances in the $D^+\to K^-K^+K^+$ decay

We study theoretically the resonant structure of the double Cabibbo suppressed $D^+\to K^- K^+K^+$ decay. We start from an elementary production diagram, considered subleading in previous approaches, which cannot produce a final $K^- K^+$ pair at the tree level but which we show to be able to provide the strength of the decay through final meson-meson state interaction. The different meson-meson elementary productions are related through SU(3) and the final rescattering is implemented from a suitable implementation of unitary extensions of ChPT which generate dynamically the scalar resonances $f_0(980)$ and $a_0(980)$. We obtain a good agreement with recent experimental data from the LHCb collaboration with a minimal freedom in the fit and show the dominance of the $a_0(980)$ contribution close to the threshold of the $K^- K^+$ spectrum.

hep-ph↗

arXiv2020

Few-body systems consisting of mesons

We present a work which is meant to inspire the few-body practitioners to venture into the study of new, more exotic, systems and to hadron physicists, working mostly on two-body problems, to move in the direction of studying related few-body systems. For this purpose we devote the discussions in the introduction to show how the input two-body amplitudes can be easily obtained using techniques of the chiral unitary theory, or its extensions to the heavy quark sector. We then briefly explain how these amplitudes can be used to solve the Faddeev equations or a simpler version obtained by treating the three-body scattering as that of a particle on a fixed center. Further, we give some examples of the results obtained by studying systems involving mesons. We have also addressed the field of many meson systems, which is currently almost unexplored, but for which we envisage a bright future. Finally, we give a complete list of works dealing with unconventional few-body systems involving one or several mesons, summarizing in this way the findings on the topic, and providing a motivation for those willing to investigate such systems.

nucl-th↗

arXiv2020

Tau decay into $\nu_\tau$ and $a_1(1260)$, $b_1(1235)$, and two $K_1(1270)$

We study the $\tau \to \nu_\tau A$ decay, with $A$ an axial-vector meson. We produce the $a_1(1260)$ and $b_1(1235)$ resonances in the Cabibbo favored mode and two $K_1(1270)$ states in the Cabibbo suppressed mode. We take advantage of previous chiral unitary approach results where these resonances appear dynamically from the vector and pseudoscalar meson interaction in s-wave. Actually two different poles were obtained associated to the $K_1(1270)$ quantum numbers. We find that the unmeasured rates for $b_1(1235)$ production are similar to those of the $a_1(1260)$ and for the two $K_1$ states we suggest to separate the present information on the $\bar K \pi \pi$ invariant masses into $\bar K^* \pi$ and $\rho K$ modes, the channels to which these two resonances couple most strongly, predicting that these modes peak at different energies and have different widths. These measurements should shed light on the existence of these two $K_1$ states.

hep-ph↗

arXiv2019

Discerning the two $K_1(1270)$ poles in $D^0\to \pi^+ V P$ decay

Within the chiral unitary approach, the axial-vector resonance $K_1(1270)$ has been predicted to manifest a two-pole nature. The lowest pole has a mass of 1195 Mev and a width of 246 Mev and couples mostly to $K^*\pi$, and the highest pole has a mass of 1284 Mev and a width of 146 Mev and couples mostly to $\rho K$. We analyze theoretically how this double-pole structure can show up in the $D^0\to \pi^+ VP$ decays by looking at the vector-pseudoscalar ($VP$) invariant mass distribution for different $VP$ channels, exploiting the fact that each pole couples differently to different $VP$ pairs. We find that the final $\bar K^*\pi$ and $\rho \bar K$ channels are sensible to the different poles of the $K_1(1270)$ resonance and hence are suitable reactions to analyze experimentally the double pole nature of this resonance.

hep-ph↗

arXiv2018

$\tau$ decay into a pseudoscalar and an axial-vector meson

We study theoretically the decay $\tau^- \to \nu_\tau P^- A$, with $P^-$ a $\pi^-$ or $K^-$ and $A$ an axial-vector resonance $b_1(1235)$, $h_1(1170)$, $h_1(1380)$, $a_1(1260)$, $f_1(1285)$ or any of the two poles of the $K_1(1270)$. The process proceeds through a triangle mechanism where a vector meson pair is first produced from the weak current and then one of the vectors produces two pseudoscalars, one of which reinteracts with the other vector to produce the axial resonance. For the initial weak hadronic production we use a recent formalism to account for the hadronization after the initial quark-antiquark pair produced from the weak current, which explicitly filters G-parity states and obtain easy analytic formulas after working out the angular momentum algebra. The model also takes advantage of the chiral unitary theories to evaluate the vector-pseudoscalar amplitudes, where the axial-vector resonances were obtained as dynamically generated from the VP interaction. We make predictions for invariant mass distribution and branching ratios for the channels considered.

hep-ph↗

arXiv2018

Triangle singularity in $\tau \to f_1(1285)\pi\nu_\tau$ decay

We show that the $\tau^-$ decay into $f_1(1285)\pi^-\nu_\tau $ is dominated by a triangle loop mechanism with $K^*$, $\bar K^*$ and $K$ (or $\bar K$) as internal lines, which manifests a strong enhancement reminiscent of a nearby singularity present in the narrow $K^*$ limit. The $f_1(1285)$ is then produced by its coupling to the $K^*\bar K$ and $\bar K^*K$ which is obtained from a previous model where this resonance was dynamically generated as a molecular $K^*\bar K$ (or $\bar K^*K$) state using the techniques of the chiral unitary approach. We make predictions for the $f_1 \pi$ mass distribution which significantly deviates from the phase-space shape, due to the distortion caused by the triangle singularity. We find a good agreement with the experimental value within uncertainties for the integrated partial decay width, which is a clear indication of the importance of the triangle singularity in this decay and supports the dynamical origin of the $f_1(1285)$ as a $K^*\bar K$ and $\bar K^* K$ molecular state.

hep-ph↗

arXiv2018

Prediction of new states from $D^{()}B^{()}\bar{B}^{(*)}$ three-body interactions

We study three-body systems composed of $D^{(*)}$, $B^{(*)}$ and $\bar{B}^{(*)}$ in order to look for possible bound states or resonances. In order to solve the three-body problem, we use the fixed center approach for the Faddeev equations considering that the $B^*\bar{B}^*(B\bar{B})$ are clusterized systems, generated dynamically, which interact with a third particle $D(D^*)$ whose mass is much smaller than the two-body bound states forming the cluster. In the $DB^*\bar{B}^*$, $D^*B^*\bar{B}^*$, $DB\bar{B}$ and $D^*B\bar{B}$ systems with $I=1/2$, we found clear bound state peaks with binding energies typically a few tens MeV and more uncertain broad resonant states about ten MeV above the threshold with widths of a few tens MeV.

hep-ph↗

arXiv2017

On the binding of the $BD\bar{D}$ and $BDD$ systems

We study theoretically the $BD\bar{D}$ and $BDD$ systems to see if they allow for possible bound or resonant states. The three-body interaction is evaluated implementing the Fixed Center Approximation to the Faddeev equations which considers the interaction of a $D$ or $\bar{D}$ particle with the components of a $BD$ cluster, previously proved to form a bound state. We find an $I(J^P)=1/2(0^-)$ bound state for the $BD\bar{D}$ system at an energy around $8925-8985$ MeV within uncertainties, which would correspond to a bottom--hidden-charm meson. In contrast, the $BDD$ system, which would be bottom--double-charm and hence manifestly exotic, we have found hints of a bound state in the energy region $8935-8985$ MeV, but the results are not stable under the uncertainties of the model, and we cannot assure, neither rule out, the possibility of a $BDD$ three-body state.

hep-ph↗

arXiv2017

Charm-beauty meson bound states from $B(B^)D(D^)$ and $B(B^)\bar D(\bar D^)$ interaction

We evaluate the s-wave interaction of pseudoscalar and vector mesons with both charm and beauty to investigate the possible existence of molecular $BD$, $B^*D$, $BD^*$, $B^*D^*$, $B\bar D$, $B^*\bar D$, $B\bar D^*$ or $B^* \bar D^*$ meson states. The scattering amplitude is obtained implementing unitarity starting from a tree level potential accounting for the dominant vector meson exchange. The diagrams are evaluated using suitable extensions to the heavy flavor sector of the hidden gauge symmetry Lagrangians involving vector and pseudoscalar mesons{, respecting heavy quark spin symmetry}. We obtain bound states at energies above 7 GeV for $BD$ ($J^P=0^+$), $B^*D$ ($1^+$), $BD^*$ ($1^+$) and $B^*D^*$ ($0^+$, $1^+$, $2^+$), all in isospin 0. For $B\bar D$ ($0^+$), $B^*\bar D$ ($1^+$), $B\bar D^*$ ($1^+$) and $B^*\bar D^*$ ($0^+$, $1^+$, $2^+$) we also find similar bound states in $I=0$, but much less bound, which would correspond to exotic meson states with $\bar b$ and $\bar c$ quarks, and for the $I=1$ we find a repulsive interaction. We also evaluate the scattering lengths in all cases, which can be tested in current investigations of lattice QCD.

hep-ph↗