Baryon Resonances Research Articles

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.

A relativistic model for the light baryon masses in hypercentral potential and spin-flavor dependence

In this paper, we studied the light baryon resonances spectrum within a relativistically quark model based on Dirac equation and generalized Gursey Radicati mass formula (GR). For exact solving of the Dirac equation for our proposed hypercentral confining potential analytically, we used the Ansatz approach. The results of our model show that the light baryons spectrums are fairly well reproduced, thanks to the flavor-dependent interaction. The overall good description of the spectrums which we obtain shows that our model can also be used to give a fair description of the energies of the negativeparity resonance and excited multiplets, at least up to 3 GeV. Eventually, we compare the results obtained from our model with the corresponding results of the Schrodinger equation for the Coulombiclike term plus a linear confining term and we found out that our model has certainly improved the results of the non-relativistic model.

Observation of a narrow structure in1H(γ,KS0)Xvia interference withφ-meson production

We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The observed structure may be due to the interference between a strange (or anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L) photoproduction leading to the same final state. The statistical significance of the observed excess of events estimated as the log likelihood ratio of the resonant signal+background hypothesis and the phi-production based background only hypothesis corresponds to 5.3 sigma.

Baryon resonances in a chiral hadronic model for the QCD equation of state

In this paper we study the influence of hadronic resonances on the phase diagram calculated with an effective chiral flavour SU(3) model. We show that varying the couplings of the baryonic resonances to the attractive scalar and the repulsive vector fields has a major impact on the order and location of the chiral phase transition and the possible existence of a critical end point as well as on the thermodynamic properties of the model. Furthermore, we study (strange) quark number fluctuations and show the related susceptibilities both at zero baryochemical potential and when crossing the phase transition line at three different points in the T-mu plane. We obtain the best agreement with current lattice data if we choose a rather strong vector coupling which in our model limits the phase transition to a smooth crossover and implies the non-existence of a critical end point.

Properties of baryon resonances from a multichannel partial wave analysis

Properties of nucleon and Δ resonances are derived from a multichannel partial wave analysis of pion and photo-induced reactions off protons. This paper summarizes the latest results on masses, widths, and decay properties of nucleon and Δ resonances.

Baryon resonances in the relativistic mean field approach

We suggest a new approach according to which baryon resonances can be viewed as collective excitations about “intrinsic” one-quark excitations in a mean field of definite symmetry. This standpoint is justified in the limit of a large number Nc of colors. Although Nc = 3 in the real world, we obtain a good agreement with the observed resonance spectrum up to 2 GeV. A possible consequence of the scheme is the existence of new exotic charmed (and bottom) baryons that may be stable against strong decays.

Effects of pseudoscalar-baryon channels in the dynamically generated vector-baryon resonances

We study the interaction of vector mesons with the octet of stable baryons in the framework of the local hidden gauge formalism using a coupled channels unitary approach, including also the pseudoscalar-baryon channels which couple to the same quantum numbers. We examine the scattering amplitudes and their poles, which can be associated to known $J^P=1/2^-,3/2^-$ baryon resonances, and determine the role of the pseudoscalar-baryon channels, changing the width and eventually the mass of the resonances generated with only the basis of vector-baryon states.

Interactions and decays of high-spin baryon resonances

Understanding strong interactions at low energy region requires the precise knowledge on the spectra and the properties of hadrons. Such informations can be obtained through detailed and sophisticated analyses of experimental data collected from various scattering processes using electromagnetic beams or hadron beams. At present, there have been a lot of precise data collected for the production of meson-baryon final states in photon-nucleon and nucleon-nucleon scattering processes. Since the total centerof- mass energy range of such scattering experiments covers the resonance region of about 2 GeV, it is legitimate to include as many baryon resonances as possible in the analyses of the data, which requires the formalism to describe high-spin baryon resonances. Here, we use the Fronsdal method to describe high-spin baryon resonances and develop their interaction Lagrangians. We then apply this method to investigate the role of high-spin baryon resonances in the reactions of γp → KΣ (1385) and γp → K + K + Ξ − .

Resonances from PHSD

The multi-strange baryon and vector meson resonance production in relativistic nucleus-nucleus collisions is studied within the parton-hadron- string dynamics (PHSD) approach which incorporates explicit partonic degrees- of-freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation-of-state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. We find a significant effect of the partonic phase on the production of multi-strange antibaryons at SPS energies due to a slightly enhanced s¯ s pair production from massive time-like gluon decay and a larger formation of antibaryons in the hadronization process. We, futhermore, obtain a visible in-medium effects in the low mass dilepton sector from dynamical vector-meson spectral functions from SIS to SPS energies whereas at RHIC and LHC energies such medium ef- fects become more moderate. In the intermediate mass regime from 1.1 to 3 GeV pronounced traces of the partonic degrees of freedom are found at SPS energies which superseed the hadronic (multi-meson) channels as well as the correlated and uncorrelated semi-leptonic D-meson decays. The dilepton production from the strongly interacting quark-gluon-plasma (sQGP) becomes already visible at top SPS energies and more pronounced at RHIC and LHC energies.

Resonance production in p+p, p+A and A+A collisions measured with HADES

The knowledge of baryonic resonance properties and production cross sections plays an important role for the extraction and understanding of medium modifications of mesons in hot and/or dense nuclear matter. We present and dis- cuss systematics on dielectron and strangeness production obtained with HADES

Coupling vector and pseudoscalar mesons to study baryon resonances

A study of meson-baryon systems with total strangeness -1 is made within a framework based on the chiral and hidden local symmetries. These systems consist of octet baryons, pseudoscalar and vector mesons. The pseudoscalar meson-baryon (PB) dynamics has been earlier found determinant for the existence of some strangeness -1 resonances, for example, $\Lambda(1405)$, $\Lambda(1670)$, etc. The motivation of the present work is to study the effect of coupling the closed vector meson-baryon (VB) channels to these resonances. To do this, we obtain the $PB \rightarrow PB$ and $VB \rightarrow VB$ amplitudes from the t-channel diagrams and the $PB \leftrightarrow VB$ amplitudes are calculated using the Kroll-Ruddermann term where, considering the vector meson dominance phenomena, the photon is replaced by a vector meson. The calculations done within this formalism reveal a very strong coupling of the VB channels to the $\Lambda(1405)$ and $\Lambda(1670)$. In the isospin 1 case, we find an evidence for a double pole structure of the $\Sigma (1480)$ which, like the isospin 0 resonances, is also found to couple strongly to the VB channels. The strong coupling of these low-lying resonances to the VB channels can have important implications on certain reactions producing them.

Strange baryon resonances in pp collisions measured with HADES

We present an analysis of the hyperons Λ(1405) and Σ(1385) + for p+p reactions at 3.5 GeV kinetic beam energy. The data were taken with the High Acceptance Di-Electron Spectrometer (HADES). A Λ(1405) signal could be reconstructed in both charged decay channels Λ(1405)→Σ± π ∓ . The obtained statistics of the Σ(1385) + signal allows also differential studies.

Consistent interactions for high-spin fermion fields

We address the issue of consistent interactions for off-shell fermion fields of arbitrary spin. These interactions play a crucial role in the quantum hadrodynamical description of high-spin baryon resonances in hadronic processes. The Rarita-Schwinger (R-S) description of high-spin fermion fields involves unphysical degrees of freedom associated with their lower-spin content. These enter the interaction if not eliminated outright. The invariance condition of the interaction under the unconstrained R-S gauge removes the lower-spin content of the fermion propagator and leads to a consistent description of the interaction. We develop the most general consistent interaction structure for high-spin fermions. We find that the power of the momentum dependence of a consistent interaction rises with the spin of the fermion field. This leads to unphysical structures in the energy dependence of the computed tree-level cross sections when the short-distance physics is cut off with standard hadronic form factors. A spin-dependent hadronic form factor is proposed that suppresses the unphysical artifacts.

Odd-parity light baryon resonances

We use a consistent SU(6) extension of the meson-baryon chiral Lagrangian within a coupled channel unitary approach in order to calculate the T-matrix for meson-baryon scattering in s-wave. The building blocks of the scheme are the pion and nucleon octets, the rho nonet and the Delta decuplet. We identify poles in this unitary T-matrix and interpret them as resonances. We study here the non exotic sectors with strangeness S=0,-1,-2,-3 and spin J=1/2, 3/2 and 5/2. Many of the poles generated can be associated with known N, Delta, Sigma, Lambda and Xi resonances with negative parity. We show that most of the low-lying three and four star odd parity baryon resonances with spin 1/2 and 3/2 can be related to multiplets of the spin-flavor symmetry group SU(6). This study allows us to predict the spin-parity of the Xi(1620), Xi(1690), Xi(1950), Xi(2250), Omega(2250) and Omega(2380) resonances, which have not been determined experimentally yet.

Baryon formation and dissociation in dense hadronic and quark matter

We study the formation of baryons as composed of quarks and diquarks in hot and dense hadronic matter in a Nambu–Jona-Lasinio (NJL)-type model. We first solve the Dyson–Schwinger equation for the diquark propagator and then use this to solve the Dyson–Schwinger equation for the baryon propagator. We find that stable baryon resonances exist only in the phase of broken chiral symmetry. In the chirally symmetric phase, we do not find a pole in the baryon propagator. In the color-superconducting phase, there is a pole, but it has a large decay width. The diquark does not need to be stable in order to form a stable baryon, a feature typical for so-called Borromean states. Varying the strength of the diquark coupling constant, we also find similarities to the properties of an Efimov state.

Extension of the Liège intranuclear cascade model at incident energies between 2 and 12 GeV. Aspects of pion production

Abstract The validity of the standard version of the Liege Intra-Nuclear Cascade (INCL4) model, which has been shown to be quite successful for the description of spallation reactions, is limited to an upper incident energy of ∼2 GeV, because inelastic elementary processes are restricted to the excitation and de-excitation of the Delta resonance. In this paper, the INCL4 model is extended to higher incident energy by including other inelastic elementary collisions. However, excitation of heavier baryonic resonances is replaced by direct multipion production in elementary nucleon–nucleon and pion–nucleon collisions. The predictions of the modified model for production of charged pions by proton and pion beams off nuclei are compared with experimental data of the HARP Collaboration for beam energies between 2 and 12 GeV. The apparent duality between the approach based on excitation of numerous baryonic resonances and our approach is briefly discussed.

MIXING OF FERMION FIELDS OF OPPOSITE PARITIES AND BARYON RESONANCES

We consider a loop mixing of two fermion fields of opposite parities whereas the parity is conserved in Lagrangian. Such kind of mixing is specific for fermions and has no analogy in boson case. Possible applications of this effect may be related with physics of baryon resonances. The obtained matrix propagator defines a pair of unitary partial amplitudes which describe the production of resonances of spin J and different parity 1/2± or 3/2±. The use of our amplitudes for joint description of πN partial waves P13 and D13 shows that the discussed effect is clearly seen in these partial waves as the specific form of interference between resonance and background. Another interesting application of this effect may be related with partial waves S11 and P11, where the picture is more complicated due to presence of several resonance states.

MOLECULE MODEL FOR KAONIC NUCLEAR CLUSTER $\bar{K}NN$

We analyze the properties of the kaonic nuclear cluster (KNC) [Formula: see text] with the structure [Formula: see text], having the quantum numbers [Formula: see text], and treated as a quasi-bound hadronic molecule state. We describe the properties of the hadronic molecule, or the KNC [Formula: see text], in terms of vibrational degrees of freedom with oscillator wave functions and chiral dynamics. These wave functions, having the meaning of trial wave functions of variational calculations, are parametrized by the frequency of oscillations of the [Formula: see text] pair, which is fixed in terms of the binding energy of the strange baryon resonance Λ(1405), treated as a quasi-bound [Formula: see text] state. The binding energies BX and widths ΓX of the states [Formula: see text] and [Formula: see text], respectively, are calculated in the heavy-baryon approximation by using chiral Lagrangians with meson–baryon derivative couplings invariant under chiral SU (3)× SU (3) symmetry at the tree-level approximation. The results are [Formula: see text] and [Formula: see text] and, where [Formula: see text] and [Formula: see text] are the widths of non-pionic [Formula: see text], NΣ and pionic [Formula: see text] decay modes, calculated for [Formula: see text] and [Formula: see text], respectively.

A polarized 3He target for the photon beam at MAMI

A polarized 3He target has been installed for the first time inside the 4π Crystal Ball detector at the tagged photon beam of the MAinz MIcrotron (MAMI). It has been demonstrated that the system works reliably and that the polarization losses during handling of the polarized gas are under control. Initial polarization values up to 70% and total relaxation times up to 20h could be obtained during a first test beam time devoted to the measurement of the double polarized photoabsorption cross-section in the Δ(1232) baryon resonance region.

Plausible explanation for theΔ5/2+(2000)puzzle

From a Faddeev calculation for the $\pi-(\Delta\rho)_{N_{5/2^{-}}(1675)}$ system we show the plausible existence of three dynamically generated $I(J^{P})=3/2 (5/2^{+})$ baryon states below 2.3 GeV whereas only two resonances, $\Delta_{5/2^{+}}(1905)(\ast\ast\ast\ast)$ and $\Delta_{5/2^{+}}(2000)(\ast\ast),$ are cataloged in the Particle Data Book Review. Our results give theoretical support to data analyses extracting two distinctive resonances, $\Delta_{5/2^{+}}(\sim1740)$ and $\Delta_{5/2^{+}}(\sim2200),$ from which the mass of $\Delta_{5/2^{+}}(2000)(\ast\ast)$ is estimated. We propose that these two resonances should be cataloged instead of $\Delta_{5/2^{+}}(2000).$ This proposal gets further support from the possible assignment of the other baryon states found in the approach in the $I=1/2,3/2$ with $J^{P}=1/2^{+},3/2^{+},5/2^+$ sectors to known baryonic resonances. In particular, $\Delta_{1/2^{+}}(1750)(\ast)$ is naturally interpreted as a $\pi N_{1/2^{-}}(1650)$ bound state.