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A. Valcarce

Publications and source records attributed to A. Valcarce.

At least 55 records · Page 3Linked to original sources
arXiv2015

J=3/2 charmed hypertriton

By solving exact three-body equations, we study the three-baryon system with charm $+1$. We look for possible bound states using baryon-baryon interactions obtained from a chiral constituent quark model. The smaller effect of the $Λ_c \leftrightarrow Σ_c$ conversion reverses the order of the $(I,J)=(0,1/2)$ and $(I,J)=(0,3/2)$ states, rather close on the strange sector. The diminishing of the kinetic energy due to the large reduced mass gives rise to a bound state in the $(I,J)=(0,3/2)$ channel. After correcting for Coulomb effects the binding energy would be between 140 and 715 keV.

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arXiv2015

Unraveling the pattern of the $XYZ$ mesons

We present a plausible mechanism for the origin of the $XYZ$ mesons in the heavy meson spectra within a standard quark-model picture. We discuss the conditions required for the existence of four--quark bound states or resonances contributing to the heavy meson spectra, being either compact or molecular. We concentrate on charmonium and bottomonium spectra, where several new states, difficult to understand as simple quark-antiquark pairs, have been reported by different experimental collaborations. The pivotal role played by entangled meson-meson thresholds is emphasized.

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arXiv2015

Nonexistence of a $Λnn$ bound state

It has been recently suggested the existence of a neutral bound state of two neutrons and a $Λ$ hyperon, $^3_Λn$. We point out that using either simple separable potentials or a full-fledged calculation with realistic baryon-baryon interactions derived from the constituent quark cluster model there is no possibility for the existence of such a $Λnn$ bound state. For this purpose, we performed a full Faddeev calculation of the $Λnn$ system in the $(I,J^P)=(1,1/2^+)$ channel using the interactions derived from the constituent quark cluster model which describe well the two-body $NN$ and $NY$ data and the $Λnp$ hypertriton.

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arXiv2015

Multiquark contributions to charm baryon spectroscopy

We study possible multiquark contributions to the charm baryon spectrum by considering higher order Fock space components. For this purpose we perform two different calculations. In a first approach we do a coupled-channel calculation of the $ND$ system looking for molecular states. In a second step we allow for the coupling to a heavy baryon--light meson two-hadron system looking for compact exotic five--quark structures. Both calculations have been done within the framework of a chiral constituent quark model. The model, tuned in the description of the baryon and meson spectra as well as the $NN$ interaction, provides parameter-free predictions for charm $+1$ molecular or compact two-hadron systems. Unlike the $N \bar D$ system, no sharp quark-Pauli effects are found. However, the existence of different two-hadron thresholds for the five-quark system will make the coupled-channel dynamics relevant. Only a few channels are candidates to lodge molecular or compact hadrons with a five-quark structure, being specially relevant the $(T)J^P=(0)1/2^-$ and $(T)J^P=(2)5/2^-$ channels. The identification of molecular states and/or compact hadrons with multiquark components either with or without exotic quantum numbers is a challenge of different collaborations like $\bar {\rm P}$ANDA, LHCb, ExHIC or J-PARC.

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arXiv2015

Heavy flavor dibaryons

We study the two-baryon system with two units of charm looking for the possible existence of a loosely bound state resembling the $H$ dibaryon. We make use of a chiral constituent quark model tuned in the description of the baryon and meson spectra as well as the $NN$ interaction. The presence of the heavy quarks makes the interaction simpler than in light baryon systems. We analyze possible quark-Pauli effects that would be present in spin-isospin saturated channels. Our results point to the non-existence of a charmed $H$-like dibaryon, although it may appear as a resonance above the $Λ_cΛ_c$ threshold.

hep-ph↗
arXiv2015

Light $Ξ$ hypernuclei

Arguments in favor of a light $ΞNN$ hypernucleus with $(I)J^P=(3/2)1/2^+$ are presented, within the uncertainties of our knowledge of the baryon-baryon strangeness $-2$ interactions. If bound, this $ΞNN$ state, being decoupled from the lowest $NΛΛ$ system, would be stable. It will also benefit from additional binding due to the electromagnetic interaction what makes it worthwhile to look for. We show how the equivalent state with $J=3/2$ could never be bound in spite of the attractive interaction of the two-body subsystems. We illustrate our discussion with a full-fledged Faddeev calculation of the $ΞNN$ system using simple potentials that mimic more elaborate interactions. We also make contact with different recent phenomenological interactions from the literature, like the ESC08 Nijmegen potential or quark-model based potentials.

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arXiv2015

Heavy-baryon quark model picture from lattice QCD

The ground state and excited spectra of baryons containing three identical heavy quarks, $b$ or $c$, have been recently calculated in nonperturbative lattice QCD. The energy of positive and negative parity excitations has been determined with high precision. Lattice results constitute a unique opportunity to learn about the quark-confinement mechanism as well as elucidating our knowledge about the nature of the strong force. We analyze the nonperturbative lattice QCD results by means of heavy-quark static potentials derived using SU(3) lattice QCD. We make use of different numerical techniques for the three-body problem.

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arXiv2015

Constituent-quark model description of triply heavy-baryon nonperturbative lattice QCD data

This paper provides results for the spectra of triply charmed and bottom baryons based on a constituent quark model approach. We take advantage of the assumption that potential models are expected to describe triply heavy baryons to a similar degree of accuracy as the successful results obtained in the charmonium and bottomonium sectors. The high precision calculation of the ground state and positive and negative parity excited states recently reported by nonperturbative lattice QCD provides us with a unique opportunity to confront model predictions with data. This comparison may also help to build a bridge between two difficult to reconcile lattice QCD results, namely, the lattice SU(3) QCD static three-quark potential and the recent results of nonperturbative lattice QCD for the triply heavy-baryon spectra.

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arXiv2014

Pion-assisted charmed dibaryon candidate

The Lambda_c(2286)-N system is studied in a chiral constituent quark model and the resulting s-wave interaction is used in separable form within three-body models of the pi-Lambda_c-N system with quantum numbers (C,I,JP)=(+1,3/2,2+). Separable interactions are also used for the dominant p-wave pion-baryon channels dominated by the Delta(1232) and Sigma_c(2520) resonances. Faddeev equations with relativistic kinematics are solved on the real axis to search for bound states and in the complex plane to search for three-body resonances. Some of the models considered generate a very narrow bound state, requiring isospin violation for its strong decay. Other models lead to a narrow resonance (Gamma < 0.4 MeV) for resonance mass below the Sigma_c(2455)-N threshold. This would be the lowest-lying C=+1 dibaryon, with mass estimated approximately as 3370+/-15 MeV.

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arXiv2012

Stability of multiquarks in an improved flip-flop model of confinement

We review some recent studies on the string model of confinement inspired by the strong-coupling regime of QCD and its application to exotic multiquark configurations. This includes two quarks and two antiquarks, four quarks and one antiquark, six quarks, and three quarks and three antiquarks with a careful treatment of the corresponding few-body problem.

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arXiv2012

Heavy hadron spectroscopy: a quark model perspective

We present recent results of hadron spectroscopy and hadron-hadron interaction from the perspective of constituent quark models. We pay special attention to the role played by higher order Fock space components in the hadron spectra and the connection of this extension with the hadron-hadron interaction. The main goal of our description is to obtain a coherent understanding of the lowenergy hadron phenomenology without enforcing any particular model, to constrain its characteristics and learn about low-energy realization of the theory.

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arXiv2012

On the proliferation of X's, Y's and Z's candidates

Heavy meson spectroscopy above open flavor thresholds has become a challenge both from the experimental and theoretical points of view. Experimentally, several signals have been interpreted as meson resonances with unusual properties; theoretically, such signals may be identified with meson-meson molecules or compact multiquark structures. We analyze the influence of thresholds on heavy meson spectroscopy comparing different flavor sectors and quantum numbers. The validity of a quark-model picture above open-flavor thresholds would severely restrict the number of channels that may lodge multiquark structures as meson-meson molecules.

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arXiv2012

Strangeness -2 hypertriton

We have solved for the first time the Faddeev equations for the bound state problem of the coupled $ΛΛN$--$ΞNN$ system to study whether an hypertriton with strangeness -2 may exist or not. We make use of the interactions obtained from a chiral quark model describing the low-energy observables of the two-baryon systems with strangeness 0, -1, and -2 and three-baryon systems with strangeness 0 and -1. The $ΛΛN$ system alone is unbound. However, when the full coupling to $ΞNN$ is considered, the strangeness -2 three-baryon system with quantum numbers $(I,J^P)=(1/2,1/2^+)$ becomes bound, with a binding energy of about 0.5 MeV. This result is compatible with the non-existence of a stable $^3_Λ$H with isospin one.

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arXiv2012

Examination of the H dibaryon within a chiral constituent quark model

We perform a coupled--channel calculation of the H dibaryon within a chiral constituent quark model. The problem is solved within a quark model constrained by the experimental data of strangeness --1 and --2 two--baryon systems. We examine in detail the role played by the different contributions of the interacting potential as well as the number of coupled channels considered. Special attention has been payed to the parameter dependence, flavor symmetry breaking and spatial configurations. The value extracted for the binding energy of the H dibaryon, being compatible with the restrictions imposed by the Nagara event, falls within a plausible extrapolation of recent lattice QCD results.

hep-ph↗
arXiv2012

$N\bar D $ system: A challenge for $\bar {\rm P}$ANDA

We study the $N \bar D$ system by means of a chiral constituent quark model. This model, tuned in the description of the baryon and meson spectra as well as the $NN$ interaction, provides parameter-free predictions for the charm -1 two-hadron systems. The presence of a heavy antiquark makes the interaction rather simple. We have found sharp quark-Pauli effects in some particular channels, generating repulsion, due to lacking degrees of freedom to accommodate the light quarks. Our results point to the existence of an attractive state, the $Δ\bar D^*$ with $(T,S)=(1,5/2)$, presenting a resonance close to threshold. It would show up in the scattering of $\bar D$ mesons on nucleons as a D wave state with quantum numbers $(T)J^P=(1)5/2^-$. This resonance resembles our findings in the $ΔΔ$ system, that offered a plausible explanation to the cross section of double-pionic fusion reactions through the so-called {\it ABC} effect. The study of the interaction of $D$ mesons with nucleons is a goal of the $\bar {\rm P}$ANDA Collaboration at the European facility FAIR and, thus, the present theoretical study is a challenge to be tested at the future experiments.

hep-ph↗
arXiv2012

Too many $X's$, $Y's$ and $Z's$?

A large number of new states have been reported during the last few years in charmonium spectroscopy above the charmed meson production threshold. They have been called $X's$, $Y's$, and $Z's$. We reflect on the influence of thresholds on heavy meson spectroscopy comparing different flavor sectors and quantum numbers. The validity of a quark-model picture above open-flavor thresholds would severely restrict the number of channels that may lodge meson-meson molecules.

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arXiv2010

The few body problem of the quark-model hadron structure

We discuss recent results of hadron spectroscopy and hadron-hadron interaction within a quark model framework. New experimental data could point to the important role played by higher order Fock space components on low-energy observables. Our aim is to obtain a coherent description of the low-energy hadron phenomenology to constrain QCD phenomenological models and try to learn about low-energy realizations of the theory. This long-range effort is based in adapting few-body techniques to study many-quark systems.

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