arXiv subjects

A. Valcarce

Publications and source records attributed to A. Valcarce.

At least 91 records · Page 5Linked to original sources

arXiv2008

Simulation of symmetric nuclei and the role of Pauli potential in binding energies and radii

It is shown that the use of a density dependent effective Pauli potential together with a nucleon-nucleon interaction potential plays a crucial role to reproduce not only the binding energies but also the matter root mean square radii of medium mass range spin-isospin saturated nuclei. This study is performed with a semiclassical Monte Carlo many-body simulation within the context of a simplified nucleon-nucleon interaction to focus on the effect of the genuine correlations due to the fermionic nature of nucleons. The procedure obtained is rather robust and it does not depend on the detailed features of the nucleon-nucleon interaction. For nuclei below saturation the density dependence may be represented in terms either of the nucleon number, $A$, or the associated Fermi momenta. When testing the simulation procedure for idealized "infinite" symmetric nuclear matter within the corresponding range of densities, it turns out that finite size effects affect the Pauli potential strength parametrization in systems up to about 120 particles while remaining approximately stable for larger systems.

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arXiv2008

Binding energies and modelling of nuclei in semiclassical simulations

We study the binding energies of spin-isospin saturated nuclei with nucleon number $8 \le A \le 100$ in semiclassical Monte Carlo many-body simulations. The model Hamiltonian consists of, (i) nucleon kinetic energy, (ii) a nucleon-nucleon interaction potential, and (iii) an effective Pauli potential which depends on density. The basic ingredients of the nucleon-nucleon potential are, a short-range repulsion, and a medium-range attraction. Our results demonstrate that one can always expect to obtain the empirical binding energies for a set of nuclei by introducing a proper density dependent Pauli potential. The present work suggests a simple, pragmatic procedure for modelling a set of nuclei calibrated by the empirical binding energies for a given NN interaction potential. Then, each set of modelled nuclei can be tested by studying other properties of nuclei in semiclassical simulations.

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arXiv2007

Baryon spectroscopy in constituent quark models

We present a study of the baryon spectra for all flavor sectors within a constituent quark model. We address some of the outstanding problems in baryon spectroscopy, as for example the spin splitting evolution for te different flavor sectors, the flavor independence of confinement and the missing state problem.

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arXiv2007

Charm Physics: Hints for a Mature Description of Hadrons

The physics of charm has become one of the best laboratories exposing the limitations of the naive constituent quark model and also giving hints into a more mature description of hadron spectroscopy. Recent discoveries are a challenge that have revolutionized our understanding of the hadron spectra. In this talk we address the study of many-quark components in charmonium spectra. To make the physics clear we also discuss exotic many-quark systems.

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arXiv2007

Quark-model hadron structure

We review some selected recent results on hadron spectroscopy and related theoretical studies based on constituent quark models.

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arXiv2007

On the existence of exotic and non-exotic multiquark meson states

To obtain an exact solution of a four-body system containing two quarks and two antiquarks interacting through two-body terms is a cumbersome task that has been tackled with more or less success during the last decades. We present an exact method for the study of four-quark systems based on the hyperspherical harmonics formalism that allows us to solve it without resorting to further approximations, like for instance the existence of diquark components. We apply it to systems containing two heavy and two light quarks using different quark-quark potentials. While $QQ\bar n \bar n$ states may be stable in nature, the stability of $Q\bar Qn \bar n$ states would imply the existence of quark correlations not taken into account by simple quark dynamical models.

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arXiv2007

$nd$ scattering lengths from a quark-model based $NN$ interaction

We calculate the doublet and quartet neutron-deuteron scattering lengths using a nonlocal nucleon-nucleon interaction fully derived from quark-quark interactions. We use as input the $NN$ $^1S_0$ and $^3S_1$-${}^3 D_1$ partial waves. Our result for the quartet scattering length agrees well with the experimental value while the result for the doublet scattering length does not. However, if we take the result for the doublet scattering length together with the one for the triton binding energy they agree well with the so-called Phillips line.

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arXiv2007

B meson spectroscopy

We study the $B$ meson spectroscopy allowing the mixture of conventional $P$ wave quark-antiquark states and four-quark components. A similar picture was used to describe the new $D_J$ and $D_{sJ}$ open charm mesons. The four-quark components shift the masses of some positive parity $B_{sJ}$ states below their corresponding isospin preserving two-meson threshold and therefore they are expected to be narrow. Electromagnetic decay widths are analyzed.

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arXiv2007

Stability of multiquarks in a simple string model

A simple string model inspired by the strong-coupling regime of Quantum ChromoDynamics is used as a potential for studying the spectrum of multiquark systems with two quarks and two antiquarks, with a careful treatment of the four-body problem. It is found that the ground state is stable, lying below the threshold for dissociation into two isolated mesons.

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arXiv2007

Are there compact heavy four-quark bound states?

We present an exact method to study four-quark systems based on the hyperspherical harmonics formalism. We apply it to several physical systems of interest containing two heavy and two light quarks using different quark-quark potentials. Our conclusions mark the boundaries for the possible existence of compact, non-molecular, four-quark bound states. While $QQ\bar n \bar n$ states may be stable in nature, the stability of $Q\bar Qn \bar n$ states would imply the existence of quark correlations not taken into account by simple quark dynamical models

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arXiv2007

Do $c\bar c n\bar n$ bound states exist?

The four--quark system $c\bar c n\bar n$ is studied in the framework of the constituent quark model. Using different types of quark-quark potentials, we solve the four--body Schrödinger equation by means of the hyperspherical harmonic formalism. Exploring the low laying $J^{PC}$ states for different isospin configurations no four-quark bound states have been found. Of particular interest is the possible four-quark structure of the X(3872). We rule out the possibility that this particle is a compact tetraquark system, unless additional correlations, either in the form of diquarks or at the level of the interacting potential, not considered in simple quark models do contribute.

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arXiv2007

$ΛNN$ and $ΣNN$ systems at threshold: II. The effect of D waves

Using the two-body interactions obtained from a chiral constituent quark model we study all $ΛNN$ and $ΣNN$ states with I=0,1,2 and J=1/2,3/2 at threshold, taking into account all three-body configurations with S and D wave components. We constrain further the limits for the $ΛN$ spin-triplet scattering length a_{1/2,1}. Using the hypertriton binding energy we find a narrow interval for the possible values of the $ΛN$ spin-singlet scattering length a_{1/2,0}. We found that the $ΣNN$ system has a quasibound state in the (I,J) = (1,1/2) channel very near threshold with a width of about 2.1 MeV.

hep-ph↗

arXiv2007

Faddeev study of heavy baryon spectroscopy

We investigate the structure of heavy baryons containing a charm or a bottom quark. We employ a constituent quark model successful in the description of the baryon-baryon interaction which is consistent with the light baryon spectra. We solve exactly the three-quark problem by means of the Faddeev method in momentum space. Heavy baryon spectrum shows a manifest compromise between perturbative and nonperturbative contributions. The flavor dependence of the one-gluon exchange is analyzed. We assign quantum numbers to some already observed resonances and we predict the first radial and orbital excitations of all states with $J=1/2$ or 3/2. We combine our results with heavy quark symmetry and lowest-order SU(3) symmetry breaking to predict the masses and quantum numbers of six still non-measured ground-state beauty baryons.

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arXiv2007

$ΛNN$ and $ΣNN$ systems at threshold

We calculate the hypertriton binding energy and the $Λd$ and $Σd$ scattering lengths using baryon-baryon interactions obtained from a chiral constituent quark model. We study consistently the $ΛNN$ and $ΣNN$ systems analyzing the effect of the $Σ\leftrightarrow Λ$ conversion. Our interactions correctly predict the hypertriton binding energy. The $(I,J)=(0,3/2)$ $ΛNN$ channel is also attractive and it might have a bound state. From the condition of nonexistence of a (0,3/2) $ΛNN$ bound state, an upper limit for the spin-triplet $ΛN$ scattering length is obtained. We also present results for the elastic and inelastic $ΣN$ and $ΛN$ cross sections. The consistent description of the $ΣN$ scattering cross sections imposes a lower limit for the corresponding spin-triplet scattering lengths. In the $ΣNN$ system the only attractive channels are $(I,J)=(1,1/2)$ and $(0,1/2)$, the $(1,1/2)$ state being the most attractive one.

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arXiv2006

Hyperspherical harmonic study of identical-flavor four-quark systems

We present an exact method based on a hyperspherical harmonic expansion to study systems made of quarks and antiquarks of the same flavor. Our formalism reproduces and improves the results obtained with variational approaches. This analysis shows that identical-flavor four-quark systems with non-exotic $2^{++}$ quantum numbers may be bound independently of the quark mass. $0^{+-}$ and $1^{+-}$ states become attractive only for larger quarks masses.

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arXiv2006

Symmetry patterns in the $(N,Δ)$ spectrum

We revise the role played by symmetry in the study of the low-lying baryon spectrum and comment on the difficulties when trying to generalize the symmetry pattern to higher energy states. We show that for the $(N,Δ)$ part such a generalization is plausible allowing the identification of spectral regularities and the prediction of until now non-identified resonances.

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arXiv2006

A $SU(4)\otimes O(3)$ scheme for nonstrange baryons

We show that nonstrange baryon resonances can be classified according to multiplets of $SU(4)\otimes O(3)$. We identify spectral regularities and degeneracies that allow us to predict the high spin spectrum from 2 to 3 GeV.

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arXiv2006

Understanding open-charm mesons

We present a theoretical framework that accounts for the new $D_J$ and $D_{sJ}$ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional $P-$wave quark-antiquark states and four-quark components. The narrowest states are basically $P-$wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold. We study the electromagnetic decay widths as basic tools to scrutiny their nature.

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