Baryon Spectrum Research Articles

EXCLUSIVE MEASUREMENTS OF OMEGA ELECTROPRODUCTION OFF THE PROTON IN THE RESONANCE REGION

A complete theory of strong interactions must describe the excited baryon spectrum as well as the structure of prominent states, which reflects the dynamics of nonperturbative QCD. Beyond the discriminating power of exclusive single- and double-pion electroproduction, the ω channel provides an additional probe of high-mass excited states. The current analysis provides preliminary differential and integrated cross sections of ω electroproduction off the proton from W = 1.7 to 3.2 GeV and Q2 = 1.5 to 5.5 GeV2. The data was collected by JLab's CLAS detector during two run periods and comprises the largest sample of exclusive resonance-region ω electroproduction ever analyzed. Preliminary Legendre decomposition of the cross sections supports previous indications of s-channel contributions to cross sections in the resonance region.

Study of Charmed and Bottom Baryons in a Variational Approach and Chiral Interactions

Models have been widely used to study charmed and bottom baryons. In this work using the confining, one gluon exchange and Goldstone boson exchange terms as inter-quark interactions, we study the heavy flavour baryon spectrum in the framework of the constituent quark model. We use a variational method to solve the non-relativistic three-body problem for baryons in the hypercentral approach. The masses of heavy baryons containing one, two, and three heavy flavour quarks are found to be in accordance with the existing experimental values or with other theoretical predictions. The magnetic moments of single heavy baryons with J^p=3/2^+ are also obtained.

Ground states and excitation spectra of baryons in a non-relativistic model with the anharmonic potential

In this work the mass spectra for some of the baryon resonances of the particle data group with three and four star status are obtained, and a unified description of the ground states and excitation spectra of baryons are provided in the framework of a non-relativistic potential model. For this goal we have analytically solved the radial Schrödinger equation for three identical interacting particles with the anharmonic potential by using the Ansatz method and then we have calculated the baryon resonances spectrum by using the Gürsey Radicati mass formula (GR) and with generalized Gürsey Radicati mass formula (GGR). The results of our model show that the calculated masses of baryon resonances by using the generalized Gürsey Radicati mass formula are found to be in good agreement with the tabulations of the Particle Data Group. 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 multiples up to 3 GeV mass and negative-parity resonance. Moreover, we have shown that our model reproduces the position of the Roper resonance of the nucleon.

Lattice computations for high energy and nuclear physics

An overview is given on present lattice field theory computations. We demonstrate the progress obtained in the field due to algorithmic, conceptual and supercomputer advances. We discuss as particular examples Higgs boson mass bounds in lattice Higgs-Yukawa models and the baryon spectrum, the anomalous magnetic moment of the muon and nuclear physics for lattice QCD. We emphasize a number of major challenges lattice field theory is still facing and estimate the computational cost for simulations at physical values of the pion mass.

The Baryon-Baryon Interaction in a Quark Model with Quark - Antiquark Excitations

The flavor symmetry aspect of the hyperon-nucleon interaction is investigated in a quark model in which the (qq̄) excitations inherent in the quark-gluon interaction are explicitly incorporated into the model space. It is shown that the long range part of the hyperon-nucleon interaction generated from the (3q)-(3q) to (3q)-(3q)(qq̄) coupling kernels has similar flavor dependence to that of the SU3 OBEP, where the SU3 parameters of the coupling constants are usually selected around the SU6 values. The flavor-SU3 symmetry breaking effect is also discussed in the single baryon problem ; results are given for the baryon-meson coupling constants, the ground state baryon spectrum, and the magnetic moments of the octet baryons.

Kinematical and dynamical aspects of higher-spin bound-state equations in holographic QCD

In this paper we derive holographic wave equations for hadrons with arbitrary spin starting from an effective action in a higher-dimensional space asymptotic to anti--de Sitter (AdS) space. Our procedure takes advantage of the local tangent frame, and it applies to all spins, including half-integer spins. An essential element is the mapping of the higher-dimensional equations of motion to the light-front Hamiltonian, thus allowing a clear distinction between the kinematical and dynamical aspects of the holographic approach to hadron physics. Accordingly, the nontrivial geometry of pure AdS space encodes the kinematics, and the additional deformations of AdS space encode the dynamics, including confinement. It thus becomes possible to identify the features of holographic QCD, which are independent of the specific mechanisms of conformal symmetry breaking. In particular, we account for some aspects of the striking similarities and differences observed in the systematics of the meson and baryon spectra.

Flavor structure of the excited baryon spectra from lattice QCD

Excited state spectra are calculated using lattice QCD for baryons that can be formed from $u$, $d$ and $s$ quarks, namely the $N$, $\Delta$, $\Lambda$, $\Sigma$, $\Xi$ and $\Omega$ families of baryons. Baryonic operators are constructed from continuum operators that transform as irreducible representations of SU(3)$_F$ symmetry for flavor, SU(4) symmetry for Dirac spins of quarks and O(3) symmetry for orbital angular momenta. Covariant derivatives are used to realize orbital angular momenta. Using the operators, we calculate matrices of correlation functions in order to extract excited states. The resulting lattice spectra have bands of baryonic states with well-defined total spins up to $J=7/2$. Each state can be assigned a dominant flavor symmetry and the counting of states of each flavor and spin reflects $SU(6) \times O(3)$ symmetry for the lowest negative-parity and positive-parity bands. States with strong hybrid content are identified through the dominance of chromo-magnetic operators.

Feynman scaling violation on baryon spectra in pp collisions at LHC and cosmic ray energies

A significant asymmetry in baryon/antibaryon yields in the central region of high energy collisions is observed when the initial state has nonzero baryon charge. This asymmetry is connected with the possibility of baryon charge diffusion in rapidity space. Such a diffusion should decrease the baryon charge in the fragmentation region and translate into the corresponding decrease of the multiplicity of leading baryons. As a result, a new mechanism for Feynman scaling violation in the fragmentation region is obtained. Another numerically more significant reason for the Feynman scaling violation comes from the fact that the average number of cut Pomerons increases with initial energy. We present the quantitative predictions of the Quark-Gluon String Model for the Feynman scaling violation at LHC energies and at even higher energies that can be important for cosmic ray physics.

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.

Exotic Baryons from a Heavy Meson and a Nucleon

We evaluate a hadronic molecule formed by a heavy meson and a nucleon respecting heavy quark symmetry. The tensor force of pion exchange potential plays a dominate role to produce an strong attraction in this system. Solving coupled channel Schr\"odinger equations for PN and P* N, we find many bound and resonant states with isospin I=0 while there are few resonances in I=1 state. The rich structures with I=0 indicate that the spectrum of heavy baryons near the threshold is influenced by the contributions from such hadron composite structures.

QCD with Two Light Dynamical Chirally Improved Quarks

Results for the excited meson and baryon spectrum with two flavors of Chirally Improved sea quarks are presented. We simulate several ensembles with pion masses ranging from 250 to 600 MeV and extrapolate to the physical pion mass. Strange quarks are treated within the partially quenched approximation. Using the variational method, we investigate the content of the states. Among others, we discuss the flavor singlet/octet content of Lambda states. In general, our results compare well with experiment, in particular we get very good agreement with the �(1405) and confirm its flavor singlet nature.

Feynman Scaling Violation on Baryon Spectra in pp Collisions at LHC and Cosmic Ray Energies

Feynman Scaling Violation on Baryon Spectra in pp Collisions at LHC and Cosmic Ray Energies

Differentiating Between ${\Delta }$- and Y-string Confinement: Can One See the Difference in Baryon Spectra?

Differentiating Between ${\Delta }$- and Y-string Confinement: Can One See the Difference in Baryon Spectra?

On the consistency of recent QCD lattice data of the baryon ground-state masses

In our recent analysis of lattice data of the BMW, LHPC and PACS-CS groups we determined a parameter set of the chiral Lagrangian that allows a simultaneous description of the baryon octet and decuplet masses as measured by those lattice groups. The results on the baryon spectrum of the HSC group were recovered accurately without their inclusion into our 6 parameter fit. We show that the same parameter set provides an accurate reproduction of the recent results of the QCDSF-UKQCD group probing the baryon masses at quite different quark masses. This shows a remarkable consistency amongst the different lattice simulations. With even more accurate lattice data in the near future it will become feasible to determine all low-energy parameters relevant at N$^3$LO.

Axion as a cold dark matter candidate: Low-mass case

Axion as a coherently oscillating scalar field is known to behave as cold dark matter in all cosmologically relevant scales. For conventional axion mass with ${10}^{\ensuremath{-}5}\text{ }\text{ }\mathrm{eV}$, the axion reveals a characteristic damping behavior in the evolution of density perturbations on scales smaller than the Solar System size. The damping scale is inversely proportional to the square root of the axion mass. We show that the axion mass smaller than ${10}^{\ensuremath{-}24}\text{ }\text{ }\mathrm{eV}$ induces a significant damping in the baryonic density power spectrum in cosmologically relevant scales, thus deviating from the cold dark matter in the scale smaller than the axion Jeans scale. With such a small mass, however, our basic assumption about the coherently oscillating scalar field is broken in the early Universe. This problem is shared by other dark matter models based on the Bose-Einstein condensate and the ultralight scalar field. We introduce a simple model to avoid this problem by introducing evolving axion mass in the early Universe and present observational effects of a present-day low-mass axion on the baryon density power spectrum, the cosmic microwave background radiation temperature power spectrum, and the growth rate of baryon density perturbation. In our low-mass axion model, we have a characteristic small-scale cutoff in the baryon density power spectrum below the axion Jeans scale. The small-scale deviations from the cold dark matter model in both matter and cosmic microwave background radiation power spectra clearly differ from the ones expected in the cold dark matter model mixed with the massive neutrinos as a hot dark matter component.

Evidence for nonanalytic light quark mass dependence in the baryon spectrum

Using precise lattice QCD computations of the baryon spectrum, we present the first direct evidence for the presence of contributions to the baryon masses which are non-analytic in the light quark masses; contributions which are often denoted "chiral logarithms". We isolate the poor convergence of SU(3) baryon chiral perturbation theory to the flavor-singlet mass combination. The flavor-octet baryon mass splittings, which are corrected by chiral logarithms at next to leading order in SU(3) chiral perturbation theory, yield baryon-pion axial coupling constants D, F, C and H consistent with QCD values; the first evidence of chiral logarithms in the baryon spectrum. The Gell-Mann--Okubo relation, a flavor-27 baryon mass splitting, which is dominated by chiral corrections from light quark masses, provides further evidence for the presence of non-analytic light quark mass dependence in the baryon spectrum; we simultaneously find the GMO relation to be inconsistent with the first few terms in a taylor expansion in m_s - m_l, which must be valid for small values of this SU(3) breaking parameter. Additional, more definitive tests of SU(3) chiral perturbation theory will become possible with future, more precise, lattice calculations.

Doubly heavy spin-1/2 baryon spectrum in QCD

We calculate the mass and residue of the heavy spin-1/2 baryons containing two heavy b or c quarks in the framework of QCD sum rules. We use the most general form of the interpolating current in its symmetric and anti-symmetric forms with respect to the exchange of heavy quarks, to calculate the two-point correlation functions describing the baryons under consideration. A comparison of the obtained results with existing predictions from various approaches is also made.

Chaos in hadrons

In the last decade quantum chaos has become a well established discipline with outreach to different fields, from condensed-matter to nuclear physics. The most important signature of quantum chaos is the statistical analysis of the energy spectrum, which distinguishes between systems with integrable and chaotic classical analogues. In recent years, spectral statistical techniques inherited from quantum chaos have been applied successfully to the baryon spectrum revealing its likely chaotic behaviour even at the lowest energies. However, the theoretical spectra present a behaviour closer to the statistics of integrable systems which makes theory and experiment statistically incompatible. The usual statement of missing resonances in the experimental spectrum when compared to the theoretical ones cannot account for the discrepancies. In this communication we report an improved analysis of the baryon spectrum, taking into account the low statistics and the error bars associated with each resonance. Our findings give a major support to the previous conclusions. Besides, analogue analyses are performed in the experimental meson spectrum, with comparison to theoretical models.

Lattice baryons in the1/Nexpansion

Results are presented for hadron spectroscopy with gauge groups $SU(N)$ with $N=3$, 5, 7. Calculations use the quenched approximation. Lattice spacings are matched using the static potential. Meson spectra show independence on $N$ and vacuum-to-hadron matrix elements scale as $\sqrt{N}$. The baryon spectrum shows the excitation levels of a rigid rotor.

Spectrum of Hadrons with Strangeness

We describe a calculation of the spectrum of strange and nonstrange hadrons that simultaneously correlates the dressed-quark-core masses of meson and baryon ground- and excited-states within a single framework. The foundation for this analysis is a symmetry-preserving Dyson–Schwinger equation treatment of a vector×vector contact interaction. Our results exemplify and highlight the deep impact of dynamical chiral symmetry breaking on the hadron spectrum: an accurate description of the meson spectrum entails a similarly successful prediction of the spectrum of baryons, including those with strangeness. The analysis also provides numerous insights into baryon structure. For example, that baryon structure is largely flavour-blind, the first radial excitation of ground-state baryons is constituted almost entirely from axial-vector diquark correlations, and DCSB is the foundation for the ordering of low-lying baryon levels; viz., (1/2)+, (1/2)+, (1/2)−.