Strange Baryon Spectra Research Articles

Study of excited varvec{varXi } baryons with the overline{text{ P }}ANDA detector

The study of baryon excitation spectra provides insight into the inner structure of baryons. So far, most of the world-wide efforts have been directed towards N^* and varDelta spectroscopy. Nevertheless, the study of the double and triple strange baryon spectrum provides independent information to the N^* and varDelta spectra. The future antiproton experiment overline{text{ P }}ANDA will provide direct access to final states containing a {overline{varXi }}varXi pair, for which production cross sections up to mu text{ b } are expected in bar{text{ p }}p reactions. With a luminosity of L=10^{31} cm^{-2} s^{-1} in the first phase of the experiment, the expected cross sections correspond to a production rate of sim 10^6, text{ events }/text{day }. With a nearly 4pi detector acceptance, overline{text{ P }}ANDA will thus be a hyperon factory. In this study, reactions of the type bar{text{ p }}p rightarrow {overline{varXi }}^{+}varXi ^{*-} as well as bar{text{ p }}p rightarrow {overline{varXi }}^{*+}varXi ^{-} with various decay modes are investigated. For the exclusive reconstruction of the signal events a full decay tree fit is used, resulting in reconstruction efficiencies between 3 and 5%. This allows high statistics data to be collected within a few weeks of data taking.

Baryon Structure and Reactions from Dyson–Schwinger Equations

We discuss the light and strange baryon spectrum obtained within the Dyson–Schwinger/Bethe–Salpeter approach. We compare results from the covariant three-body Faddeev equation and its quark–diquark simplification using the same elementary quark–gluon interaction. The quark–diquark picture allows us to make predictions for excited states in the hyperon sector which can be tested by experiments.

Rescaling of quantized skyrmions: From nucleon to heavy flavored baryons

The role of rescaling (expansion or squeezing) of quantized skyrmions is studied for the spectrum of baryons beginning with nucleon and $\Delta(1232)$, and with flavors strangeness, charm or beauty. The expansion of skyrmions due to the centrifugal forces has influence on the masses of baryons without flavor ($N$ and especially $\Delta$). The rescaling of skyrmions has smaller influence on the spectrum of strange baryons, it is more important for the case of charm, and is crucial for baryons with beauty quantum number, where strong squeezing takes place. Two competing tendencies are clearly observed: expansion of skyrmions when isospin (or spin) increases, and squeezing with increasing mass of the flavor. For the case of beauty baryon $\Lambda_b$ satisfactory agreement with data can be reached for the value $r_b= F_B/F_\pi \simeq 2.6 $, for the case of $\Sigma_b$ there should be $r_b\sim 2$, so for the beauty flavor the method seems to be not quite satisfactory because of certain intrinsic discrepances. Some pentaquark states with hidden strangeness, charm or beauty are considered as well.

Missing baryonic resonances in the Hagedorn spectrum

The hadronic medium of QCD is modeled as a gas of point-like hadrons, with its composition determined by the Hagedorn mass spectrum. The spectrum consists of a discrete and a continuous part. The former is determined by the experimentally confirmed resonances tabulated by the Particle Data Group (PDG), while the latter can be extracted from the existing lattice data. This formulation of the hadron resonance gas (HRG) provides a transparent framework to relate the fluctuation of conserved charges as calculated in the lattice QCD approach to the particle content of the medium. A comparison of the two approaches shows that the equation of state is well described by the standard HRG model, which includes only a discrete spectrum of known hadrons. The corresponding description in the strange sector, however, shows clear discrepancies, thus a continuous spectrum is added to incorporate the effect of missing resonances. We propose a method to extract the strange-baryon spectrum from the lattice data. The result is consistent with the trend set by the unconfirmed strange baryons resonances listed by the PDG, suggesting that most of the missing interaction strength for the strange baryons reside in the | S| = 1 sector. This scenario is also supported by recent lattice calculations, and might be important in the energy region covered by the NICA accelerator in Dubna, where in the heavy-ion collisions, baryons are the dominating degrees of freedom in the final state.

An Interacting Quark–Diquark Model

We describe the relativistic interacting quark-diquark model formalism and its application to the calculation of strange and nonstrange baryon spectra. The results are compared to the existing experimental data. We also discuss the application of the model to the calculation of other baryon observables, like baryon magnetic moments, open-flavor strong decays and baryon masses with self-energy corrections.

Relativistic quark-diquark model of baryons with a spin-isospin transition interaction: Non-strange baryon spectrum and nucleon magnetic moments

The relativistic interacting quark-diquark model of baryons, recently developed, is here extended to introduce a spin-isospin transition interaction into the mass operator. The refined version of the model is used to calculate the non strange baryon spectrum. The results are compared to the present experimental data.

Spectrum of heavy baryons in the quark model

Single- and double- heavy baryons are studied in the constituent quark model. The model Hamiltonian is chosen as a standard one with two exceptions : (1) The color-Coulomb term depend on quark masses, and (2) an antisymmetric $LS$ force is introduced. Model parameters are fixed by the strange baryon spectra, $\Lambda$ and $\Sigma$ baryons. The masses of the observed charmed and bottomed baryons are, then, fairly well reproduced. Our focus is on the low-lying negative-parity states, in which the heavy baryons show specific excitation modes reflecting the mass differences of heavy and light quarks. By changing quark masses from the SU(3) limit to the strange quark mass, further to the charm and bottom quark masses, we demonstrate that the spectra change from the SU(3) symmetry patterns to the heavy quark symmetry ones.

Strange and nonstrange baryon spectra in the relativistic interacting quark-diquark model with a Gürsey and Radicati-inspired exchange interaction

The relativistic interacting quark-diquark model, constructed in the framework of point form dynamics, is extended to strange baryons. The strange and nonstrange baryon spectra are calculated and compared with the experimental data.

Study of Baryon Spectroscopy Using a New Potential Form

In the present work, the nonrelativistic quark model is applied to study baryon systems, where the constituent quarks are bound by a suitable hyper central potential. We proposed a new phenomenological form of the interaction potential, digamma-type potential. Using the Jacobi coordinates, the three-body wave equation is solved numerically to calculate the resonance states of theN, Δ, Λ, andΣbaryon systems. The present model contains only two adjustable parameters in addition to the quark masses. Our theoretical calculations are compared to the available experimental data and Cornell potential results. The description of the spectrum shows that the ground states of the considered light and strange baryon spectra are in general well reproduced.

The light and strange baryon spectrum in a non-relativistic hypercentral quark potential model and algebraic framework

In this paper, we studied the baryon resonances spectrum within a non-relativistically quark model using a simple approach based on the Gursey-Radicati mass formula (GR). The average energy value of each SU(6) multiplet is described using the SU(6) invariant interaction given by a hypercentral potential. In this paper the hypercentral potential is composed of four components: the oscillatory potential, color charge, the intraction quark and neutral gluon and the dipole-dipole electromagnetic interaction. The results of our model (the combination of our proposed hypercentral potential and the generalized GR mass formula to the description of the spectrum) show that the light and strange baryons spectrum are in general fairly well reproduced. The overall good description of the spectrum which we obtain shows that our model can also be used to give a fair description of the energies of the excited multiplets with more than 2GeV mass and negative-parity resonance.

Treatment of broken symmetry in the Faddeev approach to the strange baryon spectra

By solving the Faddeev equations we calculate the mass of the strange baryons in the framework of a relativistic constituent quark model. The Goldstone-boson-exchange quark-quark interaction is derived from $SU(3{)}_{F}$ symmetry, which is explicitly broken as the strange quark is much heavier. This broken symmetry can nicely be accounted for in the Faddeev framework.

A new method for obtaining the spectrum of baryon resonances in the Killingbeck potential

In this paper, we investigate the spin- and flavor-dependent SU(6) violations in the baryon resonances spectrum using a simple approach based on the Gürsey–Radicati (GR) mass formula. The relativistic energy spectrum has some very important features that makes it vastly superior to the nonrelativistic one; so, in order to obtain the average energy value of each SU(6) multiplet, we have exactly solved the Dirac equation for the Killingbeck potential analytically by using the wave function ansatz method. The results of our model (the combination of our proposed hypercentral potential and the generalized GR mass formula for the description of the spectrum) show that the strange and nonstrange baryon spectra are, in general, fairly well reproduced. The overall good description of the spectrum which we obtain shows that our model can also be used to give a fair description of the energies of the excited multiplets with more than 2 GeV mass and negative-parity resonance. Moreover, we have shown that our model reproduces the position of the Roper resonance of the nucleon. Finally, we compare the results obtained by the Dirac equation for the Killingbeck potential with the corresponding results of the Schrödinger equation for the Cornell potential and we find that our model has improved the results of the nonrelativistic model.

Spectrum of strange and nonstrange baryons by using generalized guersey radicati mass formula and hypercentral potential

Spectrum of strange and nonstrange baryons by using generalized guersey radicati mass formula and hypercentral potential

The quest for solving QCD: Simulations at light quark masses

We present lattice QCD simulation results from the European Twisted Mass Collaboration (ETMC). In particular, we show the strange baryon spectrum, list a number of precisely determined low energy constants of chiral perturbation theory and provide a first account of simulations including the strange and charm degrees of freedom.

RESULTS FROM THE ETM COLLABORATION AT LIGHT DYNAMICAL QUARK MASSES

We present lattice QCD simulation results from the European Twisted Mass Collaboration (ETMC). In particular, we present the non-perturbatively computed strange baryon spectrum, list a number of precisely determined low energy constants of chiral perturbation theory, and provide a first account of simulations including the strange and charm quark degrees of freedom.

Constituent quark model study of light- and strange-baryon spectra

We investigate the structure of the SU(3) octet and decuplet baryons employing a constituent quark model designed for the study of the baryon-baryon interaction and successfully applied to the meson spectra. The model considers through the interacting potential perturbative, one-gluon exchange, and nonperturbative, boson exchanges and confinement, aspects of the underlying theory, quantum chromodynamics (QCD). We solve the three-quark problem by means of the Faddeev method in momentum space. We analyze the effect of the different terms in the interaction and make contact with the use of relativistic kinematics. We find an explanation to the strong contribution of the pseudoscalar forces in the semirelativistic approach for the octet baryons. A phenomenological recipe for the regularization parameter of the one-gluon exchange is found.

The light-baryon spectrum in a relativistic quark model with instanton-induced quark forces

This is the third of a series of papers treating light baryon resonances up to 3 GeV within a relativistically covariant quark model based on the Bethe-Salpeter equation with instantaneous two- and three-body forces. In this last paper we extend our previous work on non-strange baryons to a prediction of the complete strange baryon spectrum and a detailed comparison with experiment. We apply our covariant Salpeter framework to specific quark models as introduced in the two preceding papers. Quark confinement is realized by linearly rising three-body string potentials with appropriate Dirac structures; to describe the hyperfine structure of the baryon spectrum we adopt 't Hooft's two-quark residual interaction based on QCD instanton effects. The investigation of instanton-induced effects in the baryon mass spectrum plays a central role in this work. We demonstrate that several prominent features of the excited strange mass spectrum, e.g. the low positions of the strange partners of the Roper resonance or the appearance of approximate ''parity doublets'' in the Lambda-spectrum, find a natural, uniform explanation in our relativistic quark model with instanton-induced forces.

The light-baryon spectrum in a relativistic quark model with instanton-induced quark forces

This is the second of a series of three papers treating light baryon resonances up to 3 GeV within a relativistically covariant quark model based on the three-fermion Bethe-Salpeter equation with instantaneous two- and three-body forces. In this paper we apply the covariant Salpeter framework (which we developed in the first paper) to specific quark model calculations. Quark confinement is realized by a linearly rising three-body string potential with appropriate spinorial structures in Dirac-space. To describe the hyperfine structure of the baryon spectrum we adopt 't Hooft's residual interaction based on QCD-instanton effects and demonstrate that the alternative one-gluon-exchange is disfavored phenomenological grounds. Our fully relativistic framework allows to investigate the effects of the full Dirac structures of residual and confinement forces on the structure of the mass spectrum. In the present paper we present a detailed analysis of the complete non-strange baryon spectrum and show that several prominent features of the nucleon spectrum such as e.g. the Roper resonance and approximate ''parity doublets'' can be uniformly explained due to a specific interplay of relativistic effects, the confinement potential and 't Hooft's force. The results for the spectrum of strange baryons will be discussed in a subsequent paper.

Baryons in a chiral constituent quark model

In the low-energy regime light and strange baryons should be considered as systems of constituent quarks with confining interaction and a chiral interaction that is mediated by Goldstone bosons as well as by vector and scalar mesons. The flavor-spin structure and sign of the short-range part of the spin-spin force reduces the $SU(6)_{FS}$ symmetry down to $SU(3)_F \times SU(2)_S$, induces hyperfine splittings and provides correct ordering of the lowest states with positive and negative parity. There is a cancellation of the tensor force from pseudoscalar- and vector-exchanges in baryons. The spin-orbit interactions from $\rho$-like and $\omega$-like exchanges also cancel each other in baryons while they produce a big spin-orbit force in NN system. A unified description of light and strange baryon spectra calculated in a semirelativistic framework is presented. It is demonstrated that the same short-range part of spin-spin interaction between the constituent quarks induces a strong short-range repulsion in $NN$ system when the latter is treated as $6Q$ system. Thus one can achieve a simultaneous understanding of a baryon structure and baryon-baryon interaction in the low-energy regime.

Unified description of light- and strange-baryon spectra

We present a chiral constituent-quark model for light and strange baryons providing a unified description of their ground states and excitation spectra. The model relies on constituent quarks and Goldstone bosons arising as effective degrees of freedom of low-energy QCD from the spontaneous breaking of chiral symmetry. The spectra of the three-quark systems are obtained from a precise variational solution of a Schr\"odinger-type equation with a semirelativistic Hamiltonian. The theoretical predictions are found to be in close agreement with experiment.