arXiv subjects

Francisco Fernández

Publications and source records attributed to Francisco Fernández.

17 recordsLinked to original sources

arXiv2025

Constituent-quark-model based coupled-channels calculation of the $\mathbf{bb\bar c\bar c}$ and $\mathbf{bc\bar b\bar c}$ tetraquark systems

We perform a coupled-channels study of the $bb\bar c\bar c$ and $bc\bar b\bar c$ tetraquark systems in a molecular approach using a constituent quark model which has been widely used to satisfactorily describe a broad range of properties of heavy quark hadron systems, either conventional or exotic. Within a molecular framework, the interaction in the heavy quark sector is governed by gluon exchange or confinement forces that are inherently color-dependent. While the $B_c B_c$ system contains two identical quarks, enabling stronger interactions via exchange diagrams, the forces in the $B_c \bar{B}_c$ and $(c\bar{c})-(b\bar{b})$ systems are expected to be significantly weaker. Consequently, the theoretical and experimental analysis of $B_c^{(*)} B_c^{(*)}$, $B_c^{(*)} \bar{B}_c^{(*)}$, and charmonium-bottomonium bound structures could play a crucial role in clarifying the dominant mechanisms responsible for the formation of fully-heavy tetraquarks. For the $bb\bar c\bar c$ tetraquark sector, we find several resonance states with different spin-parity quantum numbers. These resonances are characterized by their proximity, but not too close, to the $B_c^{(\ast)}B_c^{(\ast)}$ thresholds and their large total decay widths, indicating strong decay channels. In contrast, our analysis of the $bc\bar b\bar c$ tetraquark sector reveals no bound states, virtual states, or resonances; suggesting that tetraquark states of the $(c\bar c)-(b\bar b)$ or $B_c^{(\ast)}\bar B_c^{(\ast)}$ molecular type are unlikely to be formed, within our model assumptions.

hep-ph↗

arXiv2025

Digital twin with automatic disturbance detection for an expert-controlled SAG mill

This study presents the development and validation of a digital twin for a semi-autogenous grinding (SAG) mill controlled by an expert system. The digital twin integrates three key components of the closed-loop operation: (1) fuzzy logic for expert control, (2) a state-space model for regulatory control, and (3) a recurrent neural network to simulate the SAG mill process. The digital twin is combined with a statistical framework for automatically detecting process disturbances (or critical operations), which triggers model retraining only when deviations from expected behaviour are identified, ensuring continuous updates with new data to enhance the SAG supervision. The model was trained with 68 hours of operational industrial data and validated with an additional 8 hours, allowing it to predict mill behaviour within a 2.5-minute horizon at 30-second intervals with errors smaller than 5%.

eess.SY↗

arXiv2024

Digital twin with automatic disturbance detection for real-time optimization of a semi-autogenous grinding (SAG) mill

This work describes the development and validation of a digital twin for a semi-autogenous grinding (SAG) mill controlled by an expert system. The digital twin consists of three modules emulating a closed-loop system: fuzzy logic for the expert control, a state-space model for regulatory control, and a recurrent neural network for the SAG mill process. The model was trained with 68 hours of data and validated with 8 hours of test data. It predicts the mill's behavior within a 2.5-minute horizon with a 30-second sampling time. The disturbance detection evaluates the need for retraining, and the digital twin shows promise for supervising the SAG mill with the expert control system. Future work will focus on integrating this digital twin into real-time optimization strategies with industrial validation.

eess.SY↗

arXiv2024

Study of the $Ω_{ccc}Ω_{ccc}$ and $Ω_{bbb}Ω_{bbb}$ dibaryons in constituent quark model

Dibaryons are the simplest system in which the baryon-baryon interaction, and hence the underlying quark-quark interaction, can be studied in a clear way. Although the only dibaryon known today is the deuteron (and possibly the $d^*$), fully heavy dibaryons are good candidates for bound states because in such systems the kinetic energy is small and the high symmetry of the wave function favours binding. In this study, the possible existence of $Ω_{ccc}Ω_{ccc}$ and $Ω_{bbb}Ω_{bbb}$ dibaryons is investigated in the framework of a constituent quark model that satisfactorily describes the deuteron, the $d^*(2380)$ and the $NN$ interaction. $J^P=0^+$ candidates are found in both systems with binding energies of the order of MeV.

hep-ph↗

arXiv2023

Exploring $T_{ψψ}$ tetraquark candidates in a coupled-channels formalism

This study investigates the properties of the $T_{ψψ}$ tetraquark candidates within a coupled-channels calculation of the $c\bar c- c\bar c$ system, specifically focusing on the $J^P=0^\pm$, $1^\pm$, and $2^\pm$ sectors. The analysis includes various channels containing a $J/ψ$, $ψ^\prime$, $η_c$, and $η_c^\prime$ meson. By searching for poles in the scattering matrix, a total of 29 states in different $J^P$ sectors with masses ranging from 6.1 to 7.6 GeV/c$^2$ are identified. The study further investigates the masses, widths and branching ratios of these states, leading to the identification of two potential candidates for the experimental $T_{ψψ}(6200)$ tetraquark, one candidate for $T_{ψψ}(6600)$, two for $T_{ψψ}(6700)$, four for $T_{ψψ}(6900)$, and three for $T_{ψψ}(7200)$ tetraquarks. Additionally, the paper discusses strategies to discriminate between different candidates and explores possible detection channels for further $c\bar c- c\bar c$ states.

hep-ph↗

arXiv2022

Production of single-charmed baryons in a quark model approach

The production of single-charmed baryons $Λ_c^+ Λ_c^-$, $Λ_c^+ Σ_c^-$+h.c. and $Σ_c^+ Σ_c^-$ in $p\bar p$ collisions is studied in the framework of a constituent quark model which has satisfactorily described the $N\bar N$ system and the strangeness production $p\bar p\to Λ\bar Λ$, $Λ\barΣ$ and $Σ\barΣ$ processes. Predictions on the total cross sections are analyzed for different approaches to the underlying $n\bar n\to c\bar c$ process, mediated by one gluon annihilation diagrams. The results indicate that the cross section is of the order of $1$ nb between $10-14$ GeV for $Λ_c^+Λ_c^-$ and $Λ_c^+ Σ_c^-$ channels, and around $0.01-0.1$ nb for $Σ_c^+Σ_c^-$. This estimations can be relevant for their future search in facilities like $\bar{P}$ANDA.

hep-ph↗

arXiv2019

The charged $Z_c$ and $Z_b$ structures in a constituent quark model approach

The nature of the recently discovered $Z_c$ and $Z_b$ structures is intriguing. Their charge forces its minimal quark content to be $Q\bar Q q\bar q$ (where $Q=\{c,b\}$ and $q=\{u,d\}$). In this work we perform a molecular coupled-channels calculation of the $I^G(J^{PC})=1^+(1^{+-})$ charm and bottom sectors in the framework of a constituent quark model which satisfactorily describes a wide range of properties of (non-)conventional hadrons containing heavy quarks. All the relevant channels are included for each sector, i.e.: The $D^{(\ast)}\bar D^{\ast}+h.c.$, $πJ/ψ$ and $ρη_c$ channels for the $Z_c$ and $B^{(\ast)}B^{\ast}$ and $Υ(nS)π$ ($n=1,2,3$) channels for the $Z_b$ analysis. Possible structures of these resonances will be discussed.

hep-ph↗

arXiv2019

Unquenching the quark model in a non-perturbative scheme

In recent years, the discovery in quarkonium spectrum of several states not predicted by the naive quark model has awakened a lot of interest. A possible description of such states requires the enlargement of the quark model by introducing quark-antiquark pair creation or continuum coupling effects. The unquenching of the quark models is a way to take these new components into account. In the spirit of the Cornell Model, this is usually done by coupling perturbatively a quark-antiquark state with definite quantum numbers to the meson-meson channel with closest threshold. In this work we present a method to coupled quark-antiquark states with meson-meson channels, taking into account effectively the non-perturbative coupling to all quark-antiquark states with the same quantum numbers. The method will be applied to the study of the X(3872) resonance and a comparison with the perturbative calculation will be performed.

hep-ph↗

arXiv2018

The differential build-up factor

The build-factor is a magnitude which allows to correct the photon exponential attenuation model to obtain the real value of a certain dosimetric magnitude, like air exposure. Its main weaknesses are the dependences on the response function of such a magnitude, the geometry, and the source directionality. A formalism to deal with the first is presented in this work, which leads to the definition of the differential build-up factor. Analog Monte Carlo calculations were used to calculate this factor, as well as describing its uncertainty, in the 30 keV to 10 MeV energy range for the most typical materials up to 10 mean-free-paths. Coherent scattering and binding effects were considered in the simulations, which make the results suitable for calculations with the most complete descriptions of the attenuation coefficients. Differences due to geometry, source directionality, and detector response variability were typically found to be up to 30 % in the studied range.

physics.app-ph↗

arXiv2018

Pile-up corrections in laser-driven pulsed x-ray sources

A formalism for treating the pile-up produced in solid-state detectors by laser-driven pulsed x-ray sources has been developed. It allows the direct use of x-ray spectroscopy without artificially decreasing the number of counts in the detector, assuming the duration of a pulse is much shorter than the detector response time and the loss of counts from the energy window of the detector can be modeled or neglected. Experimental application shows that having a small amount of pile-up subsequently corrected improves the signal-to-noise ratio, which would be more beneficial than the strict single-hit condition usually imposed on this detectors.

physics.ins-det↗

arXiv2018

Diagnostic of electron temperature from bremsstrahlung in overdense targets

Models for characterization of laser-accelerated electron via its produced bremsstrahlung are provided for both thin and thick targets. An effective temperature functional is proposed to overcome the so-called cold and hot "temperatures" in the emission spectra, which are shown not to describe the underlying electron energy distribution. In contrast, this functional allows for identifying the real effect of a hot electron component. A false "heating" effect due to added noise is also exposed. The models are shown to be in good agreement with Monte Carlo simulations, as well as in good agreement with other experimental methods when applied to experimental data.

physics.ins-det↗

arXiv2017

Threshold effects in hadron spectrum: a new spectroscopy?

The exploration of energies above the open-flavor threshold in the meson spectra has led to the appearance of unexpected states difficult to accommodate in the naive picture of a bound state of a quark and an antiquark. Many of such states are located close to meson-meson thresholds, which suggests that molecular structures may be a relevant component in the total wave function of such resonances. In this work, the state of meson-meson molecules calculations is reviewed, using a non-relativistic constituent quark model that has been applied to a wide range of hadronic observables, and therefore all model parameters are completely constrained. The model has been able to reproduce, among others, the properties of the X(3872), described as a mixture of $c\bar c$ and $D\bar D^\ast$ states, or the spectrum of the P-wave charm-strange mesons, which are well reproduced only if $DK$ and $D^\ast K$ structures are taken into account. We show that such constituent quark model, which is able to describe the ordinary heavy meson spectra, is also capable of providing a good description of many new states recently reported.

hep-ph↗

arXiv2017

Charmonium resonances in the 3.9 GeV/$c^2$ energy region and the $X(3915)/X(3930)$ puzzle

An interesting controversy has emerged challenging the widely accepted nature of the $X(3915)$ and the $X(3930)$ resonances, which had initially been assigned to the $χ_{c0}(2P)$ and $χ_{c2}(2P)$ $c\bar c$ states, respectively. To unveil their inner structure, the properties of the $J^{PC}\!\!=\!0^{++}$ and $J^{PC}\!\!=\!2^{++}$ charmonium states in the energy region of these resonances are analyzed in the framework of a constituent quark model. Together with the bare $q\bar q$ states, threshold effects due to the opening of nearby meson-meson channels are included in a coupled-channels scheme calculation. We find that the structure of both states is dominantly molecular with a probability of bare $q\bar q$ states lower than $45\%$. Our results favor the hypothesis that $X(3915)$ and $X(3930)$ resonances arise as different decay mechanisms of the same $J^{PC}\!\!=\!2^{++}$ state. Moreover we found an explanation for the recently discovered $M=3860$ MeV$/c^2$ as a $J^{PC}\!\!=\!0^{++}$ $2P$ state and rediscovery the lost $Y(3940)$ as an additional state in the $J^{PC}\!\!=\!0^{++}$ family.

hep-ph↗

arXiv2016

Threshold effects in P-wave bottom-strange mesons

Using a nonrelativistic constituent quark model in which the degrees of freedom are quark-antiquark and meson-meson components, we have recently shown that the $D^{(\ast)}K$ thresholds play an important role in lowering the mass of the physical $D_{s0}^{\ast}(2317)$ and $D_{s1}(2460)$ states. This observation is also supported by other theoretical approaches such as lattice-regularised QCD or chiral unitary theory in coupled channels. Herein, we extend our computation to the lowest $P$-wave $B_{s}$ mesons, taking into account the corresponding $J^{P} = 0^{+}$, $1^{+}$ and $2^{+}$ bottom-strange states predicted by the naive quark model and the $BK$ and $B^{\ast}K$ thresholds. We assume that mixing with $B_{s}^{(\ast)}η$ and isospin-violating decays to $B_{s}^{(\ast)}π$ are negligible. This computation is important because there is no experimental data in the $b\bar{s}$ sector for the equivalent $j_{q}^{P}=1/2^{+}$ ($D_{s0}^{\ast}(2317)$, $D_{s1}(2460)$) heavy-quark multiplet and, as it has been seen in the $c\bar s$ sector, the naive theoretical result can be wrong by more than $100\,{\rm MeV}$. Our calculation allows to introduce the coupling with the $D$-wave $B^{\ast}K$ channel and to compute the probabilities associated with the different Fock components of the physical state.

hep-ph↗

arXiv2016

Canonical description of the new LHCb resonances

The LHCb Collaboration has recently observed four $J/ψϕ$ structures called $X(4140)$, $X(4274)$, $X(4500)$ and $X(4700)$ in the $B^{+}\to J/ψϕK^{+}$ decays. We study them herein using a nonrelativistic constituent quark model in which the degrees of freedom are quark-antiquark and meson-meson components. The $X(4140)$ resonance appears as a cusp in the $J/ψϕ$ channel due to the near coincidence of the $D_{s}^{\pm}D_{s}^{\ast\pm}$ and $J/ψϕ$ mass thresholds. The remaining three $X(4274)$, $X(4500)$ and $X(4700)$ appear as conventional charmonium states with quantum numbers $3^{3}P_{1}$, $4^{3}P_{0}$ and $5^{3}P_{0}$, respectively; and whose masses and widths are slightly modified due to their coupling with the corresponding closest meson-meson thresholds. A particular feature of our quark model is a lattice-based screened linear confining interaction that has been constrained in the light quark sector and usually produces higher excited heavy-quark states with lower masses than standard quark model predictions.

hep-ph↗

arXiv2016

Molecular components in $\mathbf{D_{s0}^{\ast}(2317)}$ and $\mathbf{D_{s1}(2460)}$ mesons

Different experiments have confirmed that the $D_{s0}^{\ast}(2317)$ and $D_{s1}(2460)$ mesons are very narrow states located, respectively, below the $DK$ and $D^{\ast}K$ thresholds. This is markedly in contrast with the expectations of naive quark models and heavy quark symmetry. We address the mass shifts of the $c\bar{s}$ ground states with quantum numbers $J^{P}=0^{+}$ ($D_{s0}^{\ast}(2317)$) and $J^{P}=1^{+}$ ($D_{s1}(2460)$) using a nonrelativistic constituent quark model in which quark-antiquark and meson-meson degrees of freedom are incorporated. The quark model has been applied to a wide range of hadronic observables and thus the model parameters are completely constrained. We observe that the coupling of the $0^{+}$ $(1^{+})$ meson sector to the $DK$ $(D^{\ast}K)$ threshold is a key feature in lowering the masses of the corresponding $D_{s0}^{\ast}(2317)$ and $D_{s1}(2460)$ states predicted by the naive quark model, but also in describing the $D_{s1}(2536)$ meson as the $1^{+}$ state of the $j_{q}^{P}=3/2^{+}$ doublet predicted by heavy quark symmetry and thus reproducing its strong decay properties. Two features of our formalism cannot be address nowadays by other approaches: the coupling of the $D$-wave $D^{\ast}K$ threshold in the $J^{P}=1^{+}$ $c\bar{s}$ channel and the computation of the probabilities associated with different Fock components in the physical state.

hep-ph↗

arXiv2016

Bottomonium spectrum revisited

We revisit the bottomonium spectrum motivated by the recently exciting experimental progress in the observation of new bottomonium states, both conventional and unconventional. Our framework is a nonrelativistic constituent quark model which has been applied to a wide range of hadronic observables from the light to the heavy quark sector and thus the model parameters are completely constrained. Beyond the spectrum, we provide a large number of electromagnetic, strong and hadronic decays in order to discuss the quark content of the bottomonium states and give more insights about the better way to determine their properties experimentally.

hep-ph↗