arXiv subjects

Jorge Segovia

Publications and source records attributed to Jorge Segovia.

At least 37 records · Page 2Linked to original sources

arXiv2022

Fully-charm and -bottom pentaquarks in a Lattice-QCD inspired quark model

The fully-charm and -bottom pentaquarks, \emph{i.e.} $cccc\bar{c}$ and $bbbb\bar{b}$, with spin-parity quantum numbers $J^P=\frac{1}{2}^-$, $\frac{3}{2}^-$ and $\frac{5}{2}^-$, are investigated within a Lattice-QCD inspired quark model, which has already successfully described the recently announced fully-charm tetraquark candidate $X(6900)$, and has also predicted several other fully-heavy tetraquarks. A powerful computational technique, based on the Gaussian expansion method combined with a complex-scaling range approach, is employed to predict, and distinguish, bound, resonance and scattering states of the mentioned five-body system. Both baryon-meson and diquark-diquark-antiquark configurations, along with all of their possible color channels are comprehensively considered. Narrow resonances are obtained in each spin-parity channel for the fully-charm and -bottom systems. Moreover, most of them seems to be compact multiquarks whose wave-functions are dominated by either hidden-color baryon-meson or diquark-diquark-antiquark structure, or by the coupling between them.

hep-ph↗

arXiv2022

Bottomonium-like tetraquarks in a chiral quark model

The low-lying bottomonium-like tetraquarks $b\bar{b}q\bar{q}$ $(q=u,\,d,\,s)$ with spin-parity $J^P=0^+$, $1^+$ and $2^+$, and isospin $I=0,\,1$ or $\frac{1}{2}$, are systematically investigated within the theoretical framework of real- and complex-scaling range of a chiral quark model, which has already been successfully applied in analysis of several multiquark systems. A complete four-body $S$-wave function, which includes meson-meson, diquark-antidiquark and K-type arrangements of quarks, along with all possible color configurations are considered. In the $b\bar{b}q\bar{q}$ $(q=u,\,d)$ tetraquark system, we found resonance states of $B^{(*)} \bar{B}^{(*)}$, $Υω$, $Υρ$ and $η_b ρ$ nature with all possible $I(J^P)$ quantum numbers. Their masses are generally located in the energy range $11.0-11.3$ GeV and their widths are less than $10$ MeV. In addition, extremely narrow resonances, with two-meson strong decay widths less than $1.5$ MeV, are obtained in both $b\bar{b}u\bar{s}$ and $b\bar{b}s\bar{s}$ tetraquark systems. Particularly, four radial excitations of $ΥK^*$ and $η_b K^*$ are found at $\sim11.1$ GeV in $J^P=0^+$, $1^+$ and $2^+$ channels of $b\bar{b}u\bar{s}$ system. One $Υ(1S)ϕ(2S)$ resonance state is obtained at $11.28$ GeV in the $J^P=1^+$ sector.

hep-ph↗

arXiv2022

Nucleon axial-vector and pseudoscalar form factors, and PCAC relations

We use a continuum quark+diquark approach to the nucleon bound-state problem in relativistic quantum field theory to deliver parameter-free predictions for the nucleon axial and induced pseudoscalar form factors, $G_A$ and $G_P$, and unify them with the pseudoscalar form factor $G_5$ or, equivalently, the pion-nucleon form factor $G_{πNN}$. We explain how partial conservation of the axial-vector current and the associated Goldberger-Treiman relation are satisfied once all necessary couplings of the external current to the building blocks of the nucleon are constructed consistently; in particular, we fully resolve the seagull couplings to the diquark-quark vertices associated with the axial-vector and pseudoscalar currents. Among the results we describe, the following are worth highlighting. A dipole form factor defined by an axial charge $g_A=G_A(0)=1.25(3)$ and a mass-scale $M_A = 1.23(3) m_N$, where $m_N$ is the nucleon mass, can accurately describe the pointwise behaviour of $G_A$. Concerning $G_P$, we obtain the pseudoscalar charge $g_p^\ast = 8.80(23)$, and find that the pion pole dominance approach delivers a reliable estimate of the directly computed result. Our computed value of the pion-nucleon coupling constant, $g_{πNN}/m_N =14.02(33)/{\rm GeV}$ is consistent with recent precision determinations.

hep-ph↗

arXiv2022

Accessing pion GPDs through the Sullivan process: is it feasible?

Describing hadronic structure is one of the most intriguing problems in physics. In this respect, generalized parton distributions (GPDs) constitute an outstanding tool, allowing to draw "three dimensional pictures" of hadron's inside. Starting from contemporary models for pion's GPDs fulfilling all constraints imposed by QCD, we compute Compton form factors (CFFs) of pions subjected to deeply virtual Compton scattering. We show the behaviour of CFFs to be gluon-dominated at EIC's kinematics. Finally we evaluate lepton-beam-spin asymmetries in the Sullivan process, demonstrating the existence of such and thus triggering optimism about the possibility of probing pion's 3D structure at electron-ion colliders.

hep-ph↗

arXiv2022

Composition of low-lying $\mathbf{J=\tfrac{3}{2}^\pm \,Δ}$-baryons

A Poincaré-covariant quark+diquark Faddeev equation is used to develop insights into the structure of the four lightest $(I,J^P=\tfrac{3}{2},\tfrac{3}{2}^\pm)$ baryon multiplets. Whilst these systems can contain isovector-axialvector and isovector-vector diquarks, one may neglect the latter and still arrive at a reliable description. The $(\tfrac{3}{2},\tfrac{3}{2}^+)$ states are the simpler systems, with features that bear some resemblance to quark model pictures, \emph{e.g}., their most prominent rest-frame orbital angular momentum component is $\mathsf S$-wave and the $Δ(1600)\tfrac{3}{2}^+$ may reasonably be viewed as a radial excitation of the $Δ(1232)\tfrac{3}{2}^+$. The $(\tfrac{3}{2},\tfrac{3}{2}^-)$ states are more complex: the $Δ(1940)\tfrac{3}{2}^-$ expresses little of the character of a radial excitation of the $Δ(1700)\tfrac{3}{2}^-$; and whilst the rest-frame wave function of the latter is predominantly $\mathsf P$-wave, the leading piece in the $Δ(1940)\tfrac{3}{2}^-$ wave function is $\mathsf S$-wave, in conflict with quark model expectations. Experiments that can test these predictions, such as large momentum transfer resonance electroexcitation, may shed light on the nature of emergent hadron mass.

hep-ph↗

arXiv2022

Special Issue on Advances in Chiral Quark Models

The number of exotic candidates in both light- and heavy-quark hadron sectors has increased dramatically since the discovery by the Belle Collaboration of the so-called $X(3872)$ in 2003. It is clear that the simple quark model picture needs an extension and thus the last twenty years have witnessed an explosion of related theoretical and experimental activity. The ultimate goal of theory is to describe the properties of exotic states from the first principles of Quantum Chromodynamics (QCD), which is the non-Abelian Quantum Field Theory that describes the strong interaction. However, since this task is quite challenging, a more modest goal to start with is the development of QCD-motivated phenomenological models that specify the colored constituents, how they are clustered, and the forces between them. This Special Issue invited contributions reporting recent advances of phenomenological quark models in the study of hadron's spectrocopy, structure, and interactions, paying special attention to the exotic candidates but without losing sight of the conventional states. In response to the call for papers, and after a comprehensive peer review process, 8 articles qualified for acceptance in the final edition of the Special Issue. The authors are from geographically distributed countries such as Spain, South Africa, Ghana, China, Brazil, Argentina. This reflects the impact of the proposed topic and the effective organization of the guest editorial team of this Special Issue.

hep-ph↗

arXiv2022

The $D_{s0}(2590)^+$ as the dressed $c\bar s(2^1S_0)$ meson in a coupled-channels calculation

The recent discovery of the $D_{s0}(2590)^+$ meson by the LHCb Collaboration has stimulated the analysis of meson-meson channels effects in the two-body quark-antiquark meson spectrum. This resonance, assigned to the radial excitation of the pseudoscalar $D_s^+$ meson, has a mass much lower than the predictions of naive quark models, which could indicate a non-negligible $D^{(*)}K^{(*)}$ coupling which reduces its mass. Based on the importance of nearby meson-meson thresholds in the dynamics of P-wave $D_s$ mesons such as the $D_{s0}^*(2317)^+$ and $D_{s1}(2460)^+$, in this work we perform a coupled-channels calculation including the $D^{(*)}K^{(*)}$, $D_s^{(*)}ω$ and $D_s^*η$ channels, and study the impact of incorporating those channels in the mass of the bare $c\bar s$. The coupling between two and four-quark sectors is done by means of the $^3P_0$ mechanism, with all the parameters constrained from previous studies of the heavy meson spectroscopy. The masses, widths and production line shapes of the resulting state are analyzed.

hep-ph↗

arXiv2021

Line shape and the experimental determination of the $J/ψ\to γη_c$ branching fraction

We study the photon spectrum line-shape of the $J/ψ\to γη_c\to γX$ decay process in a nonrelativistic effective field theory (EFT) framework of quantum chromodynamics (QCD). We take into account the finite width of the $η_c$ and include $\mathcal{O}(v^2)$ corrections. We observe that the photon spectrum line-shape is divergent at large energies due to polynomially and logarithmically divergent terms, that upon integration over the photon energies in Dimensional Regularization (DR) produce no contribution or can be renormalized. We propose to subtract these divergences at the line-shape level in a manner consistent with the calculation of the width in DR and $\overline{\hbox{MS}}$ scheme. We analyze CLEO's data with the proposed subtracted line-shape and find good agreement between the theoretical prediction and the experimental result.

hep-ph↗

arXiv2021

Pion GPDs: A path toward phenomenology

We introduce a new family of Generalised Parton Distribution models able to fulfil by construction all the theoretical properties imposed by QCD. These models are built on standard Parton Distribution Functions and extended to off-forward kinematics through a well-defined procedure. We apply this strategy on the pion, first handling a simple but insightful algebraic model, and then exploiting state-of-the-art computations obtained in continuum QCD. We compare these models with a more standard one relying on an xFitter extraction of the pion Parton Distribution Functions. The results for both quark and gluon Generalised Parton Distributions are presented and exploited for calculation of Electromagnetic, Gravitational and Compton Form Factors. Results on the latter highlight the relevance of next-to-leading order corrections, even in the so-called valence region.

hep-ph↗

arXiv2021

Hidden-charm tetraquarks with strangeness in the chiral quark model

The hidden-charm tetraquarks with strangeness, $c\bar{c}s\bar{q}$ $(q=u,\,d)$, in $J^P=0^+$, $1^+$ and $2^+$ are systematically investigated in the framework of real- and complex-scaling range of a chiral quark model, whose parameters have been fixed in advance describing hadron, hadron-hadron and multiquark phenomenology. Each tetraquark configuration, compatible with the quantum numbers studied, is taken into account; this includes meson-meson, diquark-antidiquark and K-type arrangements of quarks with all possible color wave functions in four-body sector. Among the different numerical techniques to solve the Schrödinger-like 4-body bound state equation, we use a variational method in which the trial wave function is expanded in complex-range Gaussian basis functions, which is characterized by its simplicity and flexibility. This theoretical framework has already been used to study different kinds of multiquark systems, such as the hidden-charm pentaquarks, $P^+_c$, and doubly-charmed tetraquarks, $T^+_{cc}$. The recently reported $Z_{cs}$ states by the BESIII and LHCb collaborations are generally compatible with either compact tetraquark or hadronic molecular resonance configurations in our investigation. Moreover, several additional exotic resonances are found in the mass range between 3.8 GeV and 4.6 GeV.

hep-ph↗

arXiv2021

Dynamical diquarks in the ${\boldsymbol{γ^{(\ast)} p\to N(1535)\tfrac{1}{2}^-}}$ transition

The $γ^{(\ast)}+p \to N(1535) \tfrac{1}{2}^-$ transition is studied using a symmetry-preserving regularisation of a vector$\,\otimes\,$vector contact interaction (SCI). The framework employs a Poincaré-covariant Faddeev equation to describe the initial and final state baryons as quark+di\-quark composites, wherein the diquark correlations are fully dynamical, interacting with the photon as allowed by their quantum numbers and continually engaging in breakup and recombination as required by the Faddeev kernel. The presence of such correlations owes largely to the mechanisms responsible for the emergence of hadron mass; and whereas the nucleon Faddeev amplitude is dominated by scalar and axial-vector diquark correlations, the amplitude of its parity partner, the $N(1535) \tfrac{1}{2}^-$, also contains sizeable pseudoscalar and vector diquark components. It is found that the $γ^{(\ast)}+p \to N(1535) \tfrac{1}{2}^-$ helicity amplitudes and related Dirac and Pauli form factors are keenly sensitive to the relative strengths of these diquark components in the baryon amplitudes, indicating that such resonance electrocouplings possess great sensitivity to baryon structural details. Whilst SCI analyses have their limitations, they also have the virtue of algebraic simplicity and a proven ability to reveal insights that can be used to inform more sophisticated studies in frameworks with closer ties to quantum chromodynamics.

hep-ph↗

arXiv2021

The $Z_b$ structures in a constituent quark model coupled-channels calculation

The $Z_b(10610)^\pm$ and $Z_b(10650)^\pm$ are two bottomonium-like structures discovered in the $πh_b(mP)$, $πΥ(nS)$ and $B^\ast\bar B^{(\ast)}+h.c.$ invariant mass spectra, where $m=\{1,2\}$ and $n=\{1,2,3\}$. Their nature is puzzling due to their charge, which forces its minimal quark content to be $b\bar b u\bar d$ ($b\bar b d\bar u$). Thus, it is necessary to explore four-quark systems in order to understand their inner structure. Additionally, their strong coupling to channels such as $πΥ$ and the closeness of their mass to $B^\ast\bar B^{(\ast)}$-thresholds stimulates a molecular interpretation. Within the framework of a constituent quark model which satisfactorily describes a wide range of properties of (non-)conventional hadrons containing heavy quarks, we perform a coupled-channels calculation of the $I^G(J^{PC})=1^+(1^{+-})$ hidden-bottom sector including $B^{(\ast)}\bar B^{\ast}+h.c.$, $πh_b$, $πΥ$ and $ρη_b$ channels. We analyze the line shapes in the different channels, describing the $Υ(5S)\to πB^{(*)}\bar B^{(*)}$ by means of the $^3P_0$ model. Since our description of the line shapes promising, we perform the same coupled-channels calculation for the $Z_b$'s with $J^{--}$, where $J=\{0,1,2\}$. This allows us to obtain a fair description of the corresponding line shapes. The study of the analytic structure of the $S$-matrix suggests that the experimental $Z_b$ structures arise as a combination of several poles with $J^{PC}=0^{--}$, $1^{\pm-}$ and $2^{--}$ quantum numbers nearby the $B\bar B^\ast$ and $B^\ast\bar B^\ast$ thresholds.

hep-ph↗

arXiv2021

The bosonic algebraic approach applied to the $[QQ][\bar{Q}\bar{Q}]$ tetraquarks

The exact eigenenergies of the $T_{4c}=[cc][\bar{c}\bar{c}]$, $T_{4b}=[bb][\bar{b}\bar{b}]$, and $T_{2[bc]}=[bc][\bar{b}\bar{c}]$ tetraquarks are calculated within the extended transitional Hamiltonian approach, in which the so-called Bethe \emph{ansatz} within an infinite-dimensional Lie algebra is used. We fit the parameters appearing in the transitional region from phenomenology associated with potential candidates of tetraquarks. The rotation and vibration transitional theory seems to provide a better description of heavy tetraquarks than other attempts within the same formalism. Our results indicate that the pairing strengths are large enough to provide binding; an extended comparison with the current literature is also performed.

hep-ph↗

arXiv2021

Exotic resonances of fully-heavy tetraquarks in a lattice-QCD insipired quark model

Fully-heavy tetraquark states, i.e. $cc\bar{c}\bar{c}$, $bb\bar{b}\bar{b}$, $bb\bar{c}\bar{c}$ ($cc\bar{b}\bar{b}$), $cb\bar{c}\bar{c}$, $cb\bar{b}\bar{b}$, and $cb\bar{c}\bar{b}$, are systematically investigated by means of a non-relativistic quark model based on lattice-QCD studies of the two-body $Q\bar{Q}$ interaction, which exhibits a spin-independent Cornell potential along with a spin-spin term. The four-body problem is solved using the Gaussian expansion method; additionally, the so-called complex scaling technique is employed so that bound, resonance, and scattering states can be treated on the same footing. Moreover, a complete set of four-body configurations, including meson-meson, diquark-antidiquark, and K-type configurations, as well as their couplings, are considered for spin-parity quantum numbers $J^{P(C)}=0^{+(+)}$, $1^{+(\pm)}$, and $2^{+(+)}$ in the $S$-wave channel. Several narrow resonances, with two-meson strong decay widths less than 30 MeV, are found in all of the tetraquark systems studied. Particularly, the fully-charm resonances recently reported by the LHCb Collaboration, at the energy range between 6.2 and 7.2 GeV in the di-$J/ψ$ invariant spectrum, can be well identified in our calculation. Focusing on the fully-bottom tetraquark spectrum, resonances with masses between 18.9 and 19.6 GeV are found. For the remaining charm-bottom cases, the masses are obtained within a energy region from 9.8 GeV to 16.4 GeV. All these predicted resonances can be further examined in future experiments.

hep-ph↗

arXiv2021

Masses of positive- and negative-parity hadron ground-states, including those with heavy quarks

A symmetry-preserving treatment of a vector$\times$vector contact interaction is used to compute spectra of ground-state $J^P = 0^\pm, 1^\pm$ $(f\bar g)$ mesons, their partner diquark correlations, and $J^P=1/2^\pm, 3/2^\pm$ $(fgh)$ baryons, where $f,g,h \in \{u,d,s,c,b\}$. Results for the leptonic decay constants of all mesons are also obtained, including scalar and pseudovector states involving heavy quarks. The spectrum of baryons produced by this chiefly algebraic approach reproduces the 64 masses known empirically or computed using lattice-regularised quantum chromodynamics with an accuracy of 1.4(1.2)%. It also has the richness of states typical of constituent-quark models and predicts many baryon states that have not yet been observed. The study indicates that dynamical, nonpointlike diquark correlations play an important role in all baryons; and, typically, the lightest allowed diquark is the most important component of a baryon's Faddeev amplitude.

hep-ph↗

arXiv2021

Revealing the structure of light pseudoscalar mesons at the Electron-Ion Collider

How the bulk of the Universe's visible mass emerges and how it is manifest in the existence and properties of hadrons are profound questions that probe into the heart of strongly interacting matter. Paradoxically, the lightest pseudoscalar mesons appear to be the key to the further understanding of the emergent mass and structure mechanisms. These mesons, namely the pion and kaon, are the Nambu-Goldstone boson modes of QCD. Unravelling their partonic structure and the interplay between emergent and Higgs-boson mass mechanisms is a common goal of three interdependent approaches -- continuum QCD phenomenology, lattice-regularised QCD, and the global analysis of parton distributions -- linked to experimental measurements of hadron structure. Experimentally, the foreseen electron-ion collider will enable a revolution in our ability to study pion and kaon structure, accessed by scattering from the "meson cloud" of the proton through the Sullivan process. With the goal of enabling a suite of measurements that can address these questions, we examine key reactions to identify the critical detector system requirements needed to map tagged pion and kaon cross sections over a wide range of kinematics. The excellent prospects for extracting pion structure function and form factor data are shown, and similar prospects for kaon structure are discussed in the context of a worldwide programme. Successful completion of the programme outlined herein will deliver deep, far-reaching insights into the emergence of pions and kaons, their properties, and their role as QCD's Goldstone boson modes.

nucl-ex↗

arXiv2021

Form Factors of the Nucleon Axial Current

A symmetry-preserving Poincaré-covariant quark+diquark Faddeev equation treatment of the nucleon is used to deliver parameter-free predictions for the nucleon's axial and induced pseudoscalar form factors, $G_A$ and $G_P$, respectively. The result for $G_A$ can reliably be represented by a dipole form factor characterised by an axial charge $g_A=G_A(0)=1.25(3)$ and a mass-scale $M_A = 1.23(3) m_N$, where $m_N$ is the nucleon mass; and regarding $G_P$, the induced pseudoscalar charge $g_p^\ast = 8.80(23)$, the ratio $g_p^\ast/g_A = 7.04(22)$, and the pion pole dominance Ansatz is found to provide a reliable estimate of the directly computed result. The ratio of flavour-separated quark axial charges is also calculated: $g_A^d/g_A^u=-0.16(2)$. This value expresses a marked suppression of the size of the $d$-quark component relative to that found in nonrelativistic quark models and owes to the presence of strong diquark correlations in the nucleon Faddeev wave function -- both scalar and axial-vector, with the scalar diquark being dominant. The predicted form for $G_A$ should provide a sound foundation for analyses of the neutrino-nucleus and antineutrino-nucleus cross-sections that are relevant to modern accelerator neutrino experiments.

hep-ph↗

arXiv2021

The $\mathbf{sQ\bar{q}\bar{q}}$ $\mathbf{(q=u,\,d;\, Q=c,\,b)}$ tetraquarks in the chiral quark model

The low-lying $sQ\bar{q}\bar{q}$ $(q=u,\,d,\, Q=c,\,b)$ tetraquark states with $J^P=0^+$, $1^+$ and $2^+$, and in the isoscalar and isovector sectors, are systematically investigated in the framework of real- and complex-scaling range of a chiral quark model, whose parameters have been fixed in advance describing hadron, hadron-hadron and multiquark phenomenology, and thus all results presented here are pure predictions. Each tetraquark configuration, compatible with the quantum numbers studied, is taken into account; this includes meson-meson, diquark-antidiquark and K-type arrangements of quarks with all possible color wave functions in four-body sector. Among the different numerical techniques to solve the Schrödinger-like 4-body bound state equation, we use a variational method in which the trial wave function is expanded in complex-range Gaussian basis functions, because its simplicity and flexibility. Several compact bound states and narrow resonances are found in both charm-strange $cs\bar{q}\bar{q}$ and bottom-strange $bs\bar{q}\bar{q}$ tetraquark sectors, most of them as a product of the strong coupling between the different channels. The so-called $X_{0,1}(2900)$ signals, recently found by the LHCb collaboration, are unstable in our formalism with several candidates in the single-channel computations.

hep-ph↗