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Fl. Stancu

Publications and source records attributed to Fl. Stancu.

At least 19 recordsLinked to original sources
arXiv2022

Hidden bottom pentaquark in the SU(5) version of the flavor-spin model

We generalize to five distinct flavors the flavor-spin hyperfine interaction introduced previously for four flavors and used in the study of $uudc\overline{c}$ pentaquark. As a particular case here we study the lowest states of the pentaquark $uudb\overline{b}$, of either positive or negative parity, in a constituent quark model with linear confinement and the presently extended hyperfine interaction. The positive parity states have one unit of angular momentum located in the subsystem of four quarks and are described by translationally invariant states of orbital permutation symmetry $[31]_O$ which requires the configuration $s^3 p$. The negative parity states are described by the configuration $s^4$ of permutation symmetry $[4]_O$. We show that the lowest state has the quantum numbers $J^P$ = $1/2^+$ or $3/2^+$ and I = $1/2$ and is located below the $\Sigma_b B$ threshold by - 132 MeV. We present a comparison between the spectra of $uudc\overline{c}$ and $uudb\overline{b}$ pentaquarks.

hep-ph↗
arXiv2021

Relations between strong decay widths of the $P_c$ pentaquarks in the SU(4) flavor-spin model

In a previous work we have studied the isospin 1/2 lowest positive and negative parity states of the pentaquark $uudc\overline{c}$, in a constituent quark model with a linear confinement and an SU(4) flavor-spin hyperfine interaction and we compared the results with the $P^+_c(4312)$, $P^+_c(4440)$ and $P^+_c(4457)$ pentaquarks observed at LHCb in 2019. Here we extend the previous work by calculating ratios of decay rates of the $P_c$ pentaquarks to $J/Ψ$ and $η_c$ and similarly the ratio of decay rates to $Λ_c {\bar D}^*$ and $Λ_c \bar D$. Our predictions are based on the SU(4)$\times$SU(2) structure of compact pentaquarks.

hep-ph↗
arXiv2020

Exploring the spectrum of the hidden charm strange pentaquark in an SU(4) flavor-spin model

We study the spectrum of the isoscalar pentaquark $udsc\overline{c}$, of either positive or negative parity, in a constituent quark model with linear confinement and a flavor-spin hyperfine interaction previously extended to SU(4) and used to describe the spectrum of the $uudc\overline{c}$ pentaquarks observed at LHCb in 2019. For positive parity we make a distinction between the case where one unit of angular momentum is located in the subsystem of four quarks and the case where the angular momentum is located in the relative motion between a ground state four-quark subsystem and the antiquark. The novelty is that we introduce the coupling between different flavor states, due to the breaking of exact SU(4)-flavor symmetry of the Hamiltonian model, both for positive and negative parity states. An important consequence is that the lowest state, located at 4404 MeV, has quantum numbers $J^P$ = $1/2^-$ while without coupling the lowest state has $J^P$ = $1/2^+$ or $3/2^+$.

hep-ph↗
arXiv2019

Spectrum of the $uudc \bar c$ hidden charm pentaquark with an SU(4) flavor-spin hyperfine interaction

We study a few of the lowest states of the pentaquark $uudc\overline{c}$, of positive and negative parity, in a constituent quark model with an SU(4) flavor-spin hyperfine interaction. For positive parity we introduce space wave functions of appropriate permutation symmetry with one unit of orbital angular momentum in the internal motion of the four-quark subsystem or an orbital excitation between the antiquark and the four quark subsystem which remains in the ground state. We show that the lowest positive parity states $1/2^+, 3/2^+$ are provided by the first alternative and are located below the $1/2^-$ and the $1/2^+$ states with all quarks in the ground state. We compare our results with the LHCb three narrow pentaquark structures reported in 2019.

hep-ph↗
arXiv2018

Skyrme density functional description of the double magic $^{78}$Ni nucleus

We calculate the single particle spectrum of the double magic nucleus $^{78}$Ni in a Hartree-Fock approach using the Skyrme density-dependent effective interaction containing central, spin-orbit and tensor parts. We show that the tensor part has an important effect on the spin-orbit splitting of the proton $1f$ orbit which may explain the survival of magicity so far from the stability valley. We confirm the inversion of the $1f5/2$ and $2p3/2$ levels at the neutron number 48 in the Ni isotopic chain expected from previous Monte Carlo shell model calculations and supported by experimental observation.

nucl-th↗
arXiv2017

Excited hyperons of the $N = 2$ band in the $1/N_c$ expansion

The spectrum of excited baryons in the $N$ = 2 band is reanalys9 pagesed in the $1/N_c$ expansion method, with emphasis on hyperons. Predictions are made for the classification of these excited baryons into SU(3) singlets, octets and decuplets.

hep-ph↗
arXiv2017

Stability of pentaquarks with a two- plus three-body chromoelectric interaction

We study the stability of pentaquarks within a schematic model based on SU(3) color symmetry, by taking into account algebraic arguments leading to a chromoelectric interaction containing two- and three-body parts. It has already been proven that such an interaction can influence the spectrum of ordinary baryons and the stability of tetraquarks and hexaquarks.

hep-ph↗
arXiv2017

SU(3) flavor symmetry breaking in large $N_c$ excited hyperons

The $1/N_c$ expansion method for studying the mass spectrum of excited baryons is shortly reviewed together with applications to mixed symmetric states. The $[{\bf 70, \ell^+}]$ multiplet, belonging to the $N$ = 2 band, is reanalyzed, with emphasis on hyperons and the SU(3) symmetry breaking operators entering the mass formula to first order. An important result is that the hierarchy of masses as a function of strangeness is correctly reproduced for all multiplets. Predictions for unknown excited hyperons to SU(6) $\times$ O(3) multiplets are made.

hep-ph↗
arXiv2016

X(5568) as a $s u \bar d \bar b$ tetraquark in a simple quark model

The $S$-wave eigenstates of tetraquarks of type $s u \bar d \bar b$ with J$^{P}$ = 0$^{+}$, 1$^{+}$ and 2$^{+}$ are studied within a simple quark model with chromomagnetic interaction and effective quark masses extracted from meson and baryon spectra. It is tempting to see if this spectrum can accommodate the new narrow structure X(5568), observed by the DØ~~Collaboration, but not confirmed by the LHCb Collaboration. If it exists, such a tetraquark is a system with four different flavors and its study can improve our understanding of multiquark systems. The presently calculated mass of X(5568) agrees quite well with the experimental value of he DØ~~Collaboration. Predictions are made for the spectrum of the charmed partner $s u \bar d \bar c$. However we are aware of the difficulty of extracting effective quark masses, from mesons and baryons, to be used in multiquark systems.

hep-ph↗
arXiv2016

Updated $1/N_c$ expansion analysis of $[{\bf 56, 2^+}]$ and $[{\bf 70, \ell^+}]$ baryon multiplets

The mass spectra of the $[{\bf 56, 2^+}]$ and $[{\bf 70, \ell+}]$ multiplets, both belonging to the $N$ = 2 band, is reviewed in the $1/N_c$ expansion method. Previous studies, separately made for each multiplet, are presently updated to the 2014 Particle Data Group. The mass formula including corrections up to $\mathcal{O}(1/N_c)$ and first order in SU(3) flavor symmetry breaking, has the same independent operator basis in both cases. A special emphasis is made on the role of the SU(3) symmetry breaking operators $B_i$ $(i = 1,2,3)$. This can allow for multiplet assignment of $Λ$ and $Σ$ hyperons, which generally is quite difficult to make. Tentative assignments of hyperons with two- and one-star resonances are made to the $[{\bf 70, \ell+}]$ multiplet. Another important aim is to find out whether or not a common value of the coefficient $c_1$ of the dominant operator in the mass formula, can well fit the present data in both multiplets. A negative answer, which is here the case, implies distinct Regge trajectories for symmetric and mixed symmetric states.

hep-ph↗
arXiv2015

SU(3) Clebsch-Gordan coefficients at large $N_c$

It is argued that several papers where SU(3) Clebsch-Gordan coefficients were calculated in order to describe properties of hadronic systems are, up to a phase convention, particular cases of analytic formulae derived by Hecht in 1965 in the context of nuclear physics. This is valid for irreducible representations with multiplicity one in the corresponding Clebsch-Gordan series. For multiplicity two, Hecht has proposed an alternative which can provide correct $1/N_c$ sub-leading orders in large $N_c$ studies.

hep-ph↗
arXiv2014

Baryon resonances in large $N_c$ QCD

We review the current status and present open challenges of large $N_c$ QCD baryon spectroscopy. After introducing the $1/N_c$ expansion method we first shortly revisit the latest achievements for the ground state properties. Next we discuss the applicability of this method to excited states, presenting two different approaches with their advantages and disadvantages. Selected results for the spectrum and strong and electromagnetic decays are described. We also show further developments supported by the qualitative compatibility between the quark excitation picture and the meson-nucleon scattering picture. We give a quantitative comparison between results obtained from the mass formula of the $1/N_c$ expansion method and quark models and shortly discuss the implications of different large $N_c$ limits.

hep-ph↗
arXiv2014

$[{\bf 70, \ell^+}]$ baryons in large $N_c$ QCD revisited: The effect on Regge trajectories

A simple procedure within the $1/N_c$ expansion method where all the $N_c$ quarks are treated on the same footing has been found successful in describing mixed symmetric negative parity baryon states belonging to the $[{\bf 70},\ell^-]$ multiplets %with $\ell$ = 1, 2 or 3. of the $N$ = 1 and 3 bands. Presently it is applied to mixed symmetric positive parity $[{\bf 70},0^+]$ and $[{\bf 70},2^+]$ multiplets of the $N$ = 2 band. We search for the most dominant terms in the mass formula. The results are compared to those obtained in the procedure where the system is separated into a core and an excited quark. We find that both the spin and isospin operators of the entire system of $N_c$ quarks play dominant roles in describing the data, like for negative parity states. As a by-product we present the contribution of the leading spin-isospin singlet term as a function of the band number, which hints at distinct Regge trajectories for the symmetric and mixed symmetric states.

hep-ph↗
arXiv2012

Highly excited states of baryons in large $N_c$ QCD

The masses of highly excited negative parity baryons belonging to the $N$ = 3 band are calculated in the $1/N_c$ expansion method of QCD. We use a procedure which allows to write the mass formula by using a small number of linearly independent operators. The numerical fit of the dynamical coefficients in the mass formula show that the pure spin and pure flavor terms are dominant in the expansion, like for the $N$ = 1 band. We present the trend of some important dynamical coefficients as a function of the band number $N$ or alternatively of the excitation energy.

hep-ph↗
arXiv2012

Negative parity baryons in the $1/N_c$ expansion: the three towers of states revisited

We discuss the compatibility between the quark-shell picture and the meson-nucleon scattering picture in large $N_c$ QCD for mixed symmetric $\ell$ = 1 states previously analyzed by using a simple Hamiltonian including operators up to order $\mathcal{O}(N^0_c)$ defined in the standard ground state symmetric core + excited quark procedure. Here we introduce a Hamiltonian of order $\mathcal{O}(N^0_c)$ defined in a new approach where the separation of the system into two parts is not required. Three degenerate sets of states (towers) with the same quantum numbers as in the scattering picture and in the standard procedure are obtained. Thus the 0 is equally achieved. The eigenvalues of the presently chosen Hamiltonian also have simple analytic expressions, depending linearly on the three dynamical coefficients entering the Hamiltonian. This reinforces the validity of the new approach which had already 0 described excited negative parity baryons in a large energy range.

hep-ph↗
arXiv2012

Highly excited negative parity baryons in the $1/N_c$ expansion

The masses of experimentally known highly excited baryons of negative parity supposed to belong to the $[{\bf 70},\ell^-]$ multiplets ($\ell$ = 1,2,3) of the $N = 3$ band are calculated in the $1/N_c$ expansion method to order $1/N_c$ by using a procedure which allows to considerably reduce the number of linearly independent operators entering the mass formula. The numerical fits to present data show that the coefficients encoding the QCD dynamics have large, comparable values, for the flavor and spin operators. It implies that these operators contribute dominantly to the flavor-spin SU(6) symmetry breaking, like for the $[{\bf 70},1^-]$ multiplet of the $N = 1$ band.

hep-ph↗
arXiv2011

Negative parity baryons in the $1/N_c$ expansion: the quark excitation versus the meson-nucleon resonance picture

In order to better understand the fundamental issue regarding the compatibility between the quark-shell picture and that of resonances in meson-nucleon scattering in large $N_c$ QCD we extend the work of Cohen and Lebed on mixed symmetric $\ell $ = 1 baryons to analyze excited states with $\ell $ = 3. We give an explicit proof on the degeneracy of mass eigenvalues of a simple Hamiltonian including operators up to order $\mathcal{O}(N^0_c)$ \emph{i. e.} neglecting $1/N_c$ corrections in the quark-shell picture in the large $N_c$ limit. We obtain three degenerate multiplets formed of $\ell = 3$ states, as in the case of $\ell $ = 1 baryons. The compatibility between this picture and that of resonances in meson-nucleon scattering is discussed in the light of the present results.

hep-ph↗