Nucleon States Research Articles

Ground State Nucleon, Dark Energy and Dark Matter

The recently introduced model of the nucleon as a system of three point particles predicts all characteristics of the proton and neutron with experimental precision only at condition that nucleon is the loosely bound state in system of deep potential wells. The model’s Hamiltonian contains ground state with the same parity and spin as the nucleon but with other different characteristics. Existence of this ground state nucleon means that the visible Universe is composed of excited matter. The direct transition between excited and ground states is strictly forbidden, however, stimulated emission can ignite such process. Most likely, corresponding conditions realize at supernova explosion. It is shown that presence of this matter, composed of ground state nucleons, in Universe gives the chance for consistent explanation of dark matter and dark energy phenomena.

Chiral rotational {models

The chiral rotation in atomic nuclei has attracted significant attention in recent years. This paper introduces the particle rotor model and the titled axis cranking model, which are used to analyze the chiral rotation with multi-quasiparticle configuration. {For the particle rotor model, the basis space and the method to solve the model are discussed in detail: by considering the single-particle states of valence nucleons and the selection rule of angular momentum, one can construct the strong coupling basis which is symmetrized under the point group $D_2$; the dimension of the basis space will be very large when several valence nucleons are included, thus the Lancozos method is adopted to diagonalize the large scale hamiltonian matrix. For the titled axis cranking model, two versions based on the pairing plus quadrupole model and the shell correction method are introduced respectively: the cranking Hartree-Fock-Bogoliubov equations are given starting with the two-body Routhian; the 3-dimensional tilted axis cranking solutions are discussed in the intrinsic principal axes frame, and the vector of the angular velocity is parallel with the vector of the expectation values of the angular momentum components when the self-consistent solution is obtained.} By summarizing and developing further the two models, it will be helpful to clarify the debates in the understanding of the nuclear chiral rotation.

Momentum-Dependent Symmetry Potential from Nuclear Collective Flows in Heavy Ion Collisions at Intermediate Energies**Supported by the National Natural Science Foundation of China under Grant No 11505150, the Yuncheng University Research Project under Grant No YQ-2014014, and the China Postdoctoral Science Foundation under Grant No 2015M582730.

Within the isospin-dependent quantum molecular dynamics model, we investigate the nuclear collective flows produced in semi-central 197Au+197 Au collisions at intermediate energies. The neutron–proton differential flows and difference of neutron–proton collective flows are sensitive to the momentum-dependent symmetry potential. This sensitivity is less affected by both the isoscalar part of nuclear equation of state and in-medium nucleon–nucleon cross sections. Moreover, this sensitivity becomes pronounced with increasing the rapidity cut.

Extended Goldberger-Treiman relation in a three-flavor parity doublet model

We study masses and decay widths of positive and negative parity nucleons using a three-flavor parity doublet model, in which we introduce three representations, $\left[({\bf 3} , \bar{{\bf 3}})\oplus (\bar{{\bf 3}} , {\bf 3})\right]$, $\left[({\bf 3} , {\bf 6}) \oplus ({\bf 6}, {\bf 3})\right]$, and $\left[({\bf 8} , {\bf 1}) \oplus ({\bf 1} , {\bf 8})\right]$ of the chiral U$(3)_{\rm L}\times$U$(3)_{\rm R}$ symmetry. We find an extended version of the Goldberger-Treiman relation among the mass differences and the coupling constants for pionic transitions. This relation leads to an upper bound for the decay width of $N(1440) \rightarrow N(939) + \pi$ independently of the model parameters. We perform the numerical fitting of the model parameters and derive several predictions, which can be tested in future experiments or lattice QCD analysis. Furthermore, when we use the axial coupling of the excited nucleons obtained from lattice QCD analyses as inputs, we find that the ground state nucleon $N(939)$ consists of about 80% of $\left[({\bf 3} , {\bf 6}) \oplus ({\bf 6}, {\bf 3})\right]$ component, and that the chiral invariant mass of $N(939)$ is roughly $500$ -- $800$MeV.

Formation of hidden-charm pentaquarks in photon-nucleon collisions

The cross section for formation in $\gamma + p$ collisions of the recently found hidden-charm pentaquark states $P_c(4380)$ and $P_c(4450)$ is discussed and estimated. The studies of these resonances in photon beam experiments can be complementary to those in the LHCb experiment setting, and may be more advantageous for measurement of their additional decay channels. It is pointed out that both the relative importance of such decays and the yield of the resonances in the $\gamma + p$ collisions are sensitive to the internal dynamics of the pentaquarks and can resolve between theoretical models. Specific numerical estimates are discussed within a simple `baryocharmonium' model, where the the observed $P_c$ resonances are composites of $J/\psi$ and excited nucleon states with the quantum numbers of $N(1440)$ and $N(1520)$.

Parton densities and structure functions of nucleons and light nuclei based on the modified chiral quark-exchange model

We investigate the structure of the light nuclei based on the modified chiral quark model $(\ensuremath{\chi}\mathrm{QM})$, for the first time. To this end, we first calculate the parton distribution functions (PDFs) of the bounded nucleons using the $\ensuremath{\chi}\mathrm{QM}$ and then compute those of the light nuclei. For this purpose, it is first needed to obtain the bare quark densities inside the bounded nucleons of the nucleus. These bare distributions are calculated by applying the quark exchange model (QEM) in this article. Finally, we obtain the quark, antiquark, and gluon distributions and also the structure functions (SFs) of the bound state nucleons and the light nuclei at low ${Q}^{2}$ scale $({Q}^{2}=0.35\phantom{\rule{0.16em}{0ex}}\phantom{\rule{4pt}{0ex}}{\mathrm{GeV}}^{2})$. These distributions can be evolved to the higher scales using DGLAP evolution equations. It is shown that the results of our theoretical framework are in good agreement with the experimental data and they also have appropriate behavior in comparison with the different parametrization models.

The Higgs mass derived from the U(3) Lie group

The Higgs mass value is derived from a Hamiltonian on the Lie group U(3) where we relate strong and electroweak energy scales. The baryon states of nucleon and delta resonances originate in specific Bloch wave degrees of freedom coupled to a Higgs mechanism which also gives rise to the usual gauge boson masses. The derived Higgs mass is around 125 GeV. From the same Hamiltonian, we derive the relative neutron to proton mass ratio and the N and Delta mass spectra. All compare rather well with the experimental values. We predict scarce neutral flavor baryon singlets that should be visible in scattering cross-sections for negative pions on protons, in photoproduction on neutrons, in neutron diffraction dissociation experiments and in invariant mass spectra of protons and negative pions in B-decays. The fundamental predictions are based on just one length scale and the fine structure constant. More particular predictions rely also on the weak mixing angle and the up–down quark flavor mixing matrix element. With differential forms on the measure-scaled wave function, we could generate approximate parton distribution functions for the u and d valence quarks of the proton that compare well with established experimental analysis.

Application of Straw Tube Detectors to Hyperon Studies

S. Jowzaee a,b,* for the COSY-TOF collaboration Institute of Physics, Jagiellonian University, St. Šojasiewicza 11, 30-348 Krakow, Poland Julich Center for Hadron Physics, Forschungszentrum Julich, 52428 Julich, Germany A high statistics measurement of the ~pp → pKΛ reaction was done with the COSY-TOF experiment. The proton beam was polarized up to more than 80%, and its momentum was 2.95 GeV/c. The reconstruction of the pKΛ events was done only with the straw tube tracker due to the higher spatial resolution of the straw tube tracker compared to other subdetectors. The Dalitz plot of the pKΛ events was analyzed to understand the reaction mechanism and presented in this paper. The Dalitz plot shows that the COSY-TOF experiment provides complete kinematic coverage of the phase space of this reaction which made it ideal for ~pp → pKΛ reaction analysis. The in uence of di erent physical e ects as pΛ nal state interaction, excited nucleon states (N∗-resonances) and a coupled channel e ect of NΣ-pΛ (NΣ cusp e ect) produce signi cant structures in the Dalitz plot. The angular distribution of the particles in the CMS and helicity frame was also presented in this paper.

Nuclear equation of state and finite nucleon volumes

It is shown how the equation of state (EoS) depends on nucleon properties inside nuclear matter (NM). We propose to benefit from the concept of enthalpy in order to include volume corrections to the nucleon rest energy, which are proportional to pressure and absent in a standard relativistic mean field (RMF) with point-like nucleons. As a result, the nucleon mass can decrease inside NM, making the model nonlinear and the EoS softer. The course of the EoS in our RMF model agrees with a semi-empirical estimate and is close to the results obtained from extensive DBHF calculations with a Bonn A potential, which produce an EoS stiff enough to describe neutron star properties (mass–radius constraint), especially the masses of ‘PSR J16142230’ and ‘PSR J0348 + 0432’, known as the most massive () neutron stars. The presented model has proper saturation properties, including a good value of compressibility.

Unpolarized transverse momentum dependent parton distribution functions beyond leading twist in quark models

Higher-twist transverse momentum dependent parton distribution functions (TMDs) are a valuable probe of the quark-gluon dynamics in the nucleon, and play a vital role for the explanation of sizable azimuthal asymmetries in hadron production from unpolarized and polarized deep-inelastic lepton-nucleon scattering observed in experiments at CERN, DESY and Jefferson Lab. The associated observables are challenging to interpret, and still await a complete theoretical explanation, which makes guidance from models valuable. In this work we establish the formalism to describe unpolarized higher-twist TMDs in the light-front framework based on a Fock-space expansion of the nucleon state in terms of free on-shell parton states. We derive general expressions and present numerical results in a practical realization of this picture provided by the light-front constituent quark model. We review several other popular quark model approaches including free quark ensemble, bag, spectator and chiral quark-soliton model. We discuss how higher-twist TMDs are described in these models, and obtain results for several TMDs not discussed previously in literature. This study contributes to the understanding of non-perturbative properties of subleading twist TMDs. The results from the light-front constituent quark model are also compared to available phenomenological information, showing a satisfactory agreement.

Nucleon as a Nonrelativistic Three Point Particles System

The Galilei invariant nonrelativistic model of the proton and the neutron as systems of three point particles (PP), sharing main characteristics of fundamental up and down quarks is developed. The harmonic oscillator potentials are applied for interactions of different pairs of PP’s description. To avoid the appearance of not observable bound excited states of nucleon, these potentials have finite range. The procedure of model parameters fitting gives precise values of magnetic momenta, masses and charge radii of the proton and the neutron.

Relativistic Fermi-Gas Model for Nucleus

Spin-half fermions are considered to be limited in a spherical potential well with periodic boundary conditions. The whole system is treated like a relativistic Fermi Gas. Solving the corresponding Dirac equation, the density of states, the Fermi energy, the average energy, the density of states of nucleons and the total energy of the ground-state are obtained.

Global analysis of the negative parity nonstrange baryons in the1/Ncexpansion

A global study of the negative parity non-strange baryon observables is performed in the framework of the 1/N{sub c} expansion. Masses, partial decay widths and photo-couplings are simultaneously analyzed. A main objective is to determine the composition of the spin 1/2 and 3/2 nucleon states, which come in pairs and involve two mixing angles which can be determined and tested for consistency by the mentioned observables. The issue of the assignment of those nucleon states to the broken SU(4) X O(3) mixed-symmetry multiplet is studied in detail, with the conclusion that the assignment made in the old studies based on the non-relativistic quark model is the preferred one. In addition, the analysis involves an update of the input data with respect to previous works.

Comparison of multi-ħωshell-model results with MCAS

A multi-channel algebraic scattering (MCAS) method has been used to obtain spectra of a number of light-mass nuclei, which are treated as a two-cluster system, here specifically a nucleon plus nucleus. To date, collective models have been used to specify the interactions between the nucleon and low-lying states of the nucleus that form the compound. For the case of the carbon isotopes, these studies have been complemented by sufficiently complex and complete shell-model calculations. Comparisons with the multi-ħω shell-model results provide new insights into the validity of those from MCAS.

BONN-GATCHINA ANALYSIS: DEVELOPMENT OF THE METHOD AND ANALYSIS OF NEW PHOTO-PRODUCTION DATA

The new method for a combined analysis of meson production data is presented. This method fully satisfies the unitarity and analyticity conditions and is suitable for an analysis of modern high statistic data. The results obtained in the framework of this approach are compared with the results of the K-matrix analysis. Including in the analysis of the meson production reaction the data from the γ-neutron collision allows us to extract the information about the helicity couplings [Formula: see text] and [Formula: see text] of nucleon states.

TRANSITION FORM FACTORS: A UNIQUE OPPORTUNITY TO CONNECT NON-PERTURBATIVE STRONG INTERACTIONS TO QCD

Meson-photoproduction measurements and their reaction-amplitude analyses can establish more sensitively, and in some cases in an almost model-independent way, nucleon excitations and non-resonant reaction amplitudes. However, to investigate the strong interaction from explored — where meson-cloud degrees of freedom contribute substantially to the baryon structure — to still unexplored distance scales — where quark degrees of freedom dominate and the transition from dressed to current quarks occurs — we depend on experiments that allow us to measure observables that are probing this evolving non-perturbative QCD regime over its full range. Elastic and transition form factors are uniquely suited to trace this evolution by measuring elastic electron scattering and exclusive single-meson and double-pion electroproduction cross sections off the nucleon. These exclusive measurements will be extended to higher momentum transfers with the energy-upgraded CEBAF beam at JLab to study the quark degrees of freedom, where their strong interaction is responsible for the ground and excited nucleon state formations. After establishing unprecedented high-precision data, the imminent next challenge is a high-quality analysis to extract these relevant electrocoupling parameters for various resonances that then can be compared to state-of-the-art models and QCD-based calculations. Recent results will demonstrate the status of the analysis and of their theoretical descriptions, and an experimental and theoretical outlook will highlight what shall and may be achieved in the new era of the 12-GeV upgraded transition form factor program.

Baryon Spectroscopy at ELSA and at MAMI - selected results

Spectroscopy of baryons and their excited states plays a key role for our under- standing of the strong interaction in the non-perturbative regime. Both, in theory and in experiment, large progress has been made during the last few years. The rapid develop- ments in lattice gauge calculations and the application of the Dyson-Schwinger equation to QCD have opened new perspectives for the interpretation of the excitation spectrum of the nucleon. In parallel, large efforts have been undertaken world-wide, and are still running, to investigate excited nucleon states experimentally, in particular with photon- induced production of mesons. In the present contribution we discuss such experimental programs conducted at the tagged photon beams of the electron accelerators ELSA in Bonn and MAMI in Mainz. These programs are diverse. They include the measurement of cross sections, single- and double polarization observables for single meson production and production of meson pairs off free protons as well as of quasi-free nucleons bound in the deuteron (and sometimes other light nuclei).

STUDIES OF N* STRUCTURE FROM THE CLAS MESON ELECTROPRODUCTION DATA

The transition γvpN* amplitudes (electrocouplings) for prominent excited nucleon states obtained in a wide area of photon virtualities offer valuable information for the exploration of the N* structure at different distances and allow us to access the complex dynamics of non-perturbative strong interaction. The current status in the studies of γvpN* electrocouplings from the data on exclusive meson electroproduction off protons measured with the CLAS detector at Jefferson Lab is presented. The impact of these results on exploration of the N* structure is discussed.

Baryon Structure in AdS/QCD

We discuss baryon structure in a soft-wall anti-de Sitter/quantum chromodynamics model. From unified point of view we describe nucleon form factors and the electroproduction of the N(1440) Roper resonance. The Roper resonance is identified as the first radially excited state of the nucleon. The obtained results for helicity amplitudes of the Roper electroproduction are in good agreement with the recent results of the CLAS Collaboration at JLab.

Nucleon resonances within a dynamical coupled-channels model ofπNandγNreactions

The nucleon resonances are investigated within a dynamical coupled-channels model of pi N and gamma N reactions up to the invariant mass W = 2 GeV. The meson-baryon (MB) channels included in the calculations are MB = pi N, eta N, K Lambda, K Sigma, and pi pi N that has pi Delta, rho N, and sigma N resonant components. The meson-baryon amplitudes T_{M'B',MB}(W) are calculated from solving a set of coupled-channels integral equations defined by an interaction Hamiltonian consisting of (a) meson-exchange interactions v_{M'B',MB} derived from phenomenological Lagrangian, and (b) vertex interactions N* --> MB for describing the transition of a bare excited nucleon state N* to a channel MB. The parameters of v_{M'B',MB} are mainly constrained by the fit to the data of pi N --> pi N in the low energy region up to W =1.4 GeV. The bare masses of N* and the N* --> MB parameters are then determined in simultaneous fits to the data of pi N --> pi N up to W =2.3 GeV and those of pi N --> eta N, K Lambda, K Sigma and gamma N --> pi N, eta N, K Lambda, K Sigma up to W = 2.1 GeV. The pole positions and residues of nucleon resonances are extracted by analytically continuing the meson-baryon amplitudes T_{M'B',MB}(W) to the complex Riemann energy surface. From the extracted residues, we have determined the N* --> pi N, gamma N, eta N, K Lambda, K Sigma transition amplitudes at resonance poles. We compare the resonance pole positions from our analysis with those given by Particle Data Group and the recent coupled-channels analyses by the Juelich and Bonn-Gatchina groups. Four results agree well only for the first N* in each spin-parity-isospin (J^P,I) channel. For higher mass states, the number of states and their resonance positions from four results do not agree well. We discuss the possible sources of the discrepancies and the need of additional data from new hadron facilities such as J-PARC.