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We study possible baryon molecules in the non-strange heavy baryon spectrum. We include configurations with a heavy-meson and a light baryon. We find several structures, in particular we can understand the Λ{sub c}(2940) as a D*N molecule with J{sup P} = 3/2{sup −} quantum numbers. We also find D{sup (*)}Δ candidates for the recently discovered X{sub c}(3250) resonance.
The excited baryon masses are analyzed in the framework of the 1/Nc expansion using the available physical masses and also the masses obtained in lattice QCD for different quark masses. The baryon states are organized into irreducible representations of SU(6) x O(3), where the [56,l P =0⁺] ground state and excited baryons, and the [56,2 + ] and [70}},1 - ] excited states are analyzed. The analyses are carried out to order O(1/N c ) and first order in the quark masses. The issue of state identifications is discussed. Numerous parameter independent mass relations result at those orders, among them the well known Gell-Mann-Okubo and Equal Spacing relations, as well as additional relations involving baryons with different spins. It is observed that such relations are satisfied at the expected level of precision. The main conclusion of the analysis is that qualitatively the dominant physical effects are similar for the physical and the lattice QCD baryons.
I describe recent progress at understanding the excited baryon spectrum of QCD from lattice gauge simulations. I begin by outlining the recipe for spectroscopy calculations. I compare lattice calculations of the spectrum of the baryons containing the light (u,d) and strange quarks for pion masses in excess of 400 MeV, and compare with expectations from QCD-inspired descriptions of the spectrum, before addressing the issue of unstable resonances in lattice QCD. I conclude by describing the prospects for examining the electromagnetic properties of baryon excited states from lattice gauge calculations.
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We describe the observed light-baryon spectrum by extending superconformal quantum mechanics to the light front and its embedding in AdS space. This procedure uniquely determines the confinement potential for arbitrary half-integer spin. To this end, we show that fermionic wave equations in AdS space are dual to light-front supersymmetric quantum-mechanical bound-state equations in physical space-time. The specific breaking of conformal invariance explains hadronic properties common to light mesons and baryons, such as the observed mass pattern in the radial and orbital excitations, from the spectrum generating algebra. Lastly, the holographic embedding in AdS also explains distinctive and systematic features, such as the spin-J degeneracy for states with the same orbital angular momentum, observed in the light-baryon spectrum.
Considering a 3 + 1 dimensional lattice quantum chromodynamics (QCD) model defined with the improved Wilson action, three flavors, and 4 × 4 Dirac spin matrices, in the strong coupling regime, we reanalyze the question of the existence of the eightfold way baryons and complete our previous work where the existence of isospin octet baryons was rigorously solved. Here, we show the existence of isospin decuplet baryons which are associated with isolated dispersion curves in the subspace of the underlying quantum mechanical Hilbert space with vectors constructed with an odd number of fermion and antifermion basic quark and antiquark fields. Moreover, smoothness properties for these curves are obtained. The present work deals with a case for which the traditional method to solve the implicit equation for the dispersion curves, based on the use of the analytic implicit function theorem, cannot be applied. We do not have only one but two solutions for each one-baryon decuplet sector with fixed spin third component. Instead, we apply the Weierstrass preparation theorem, which also provides a general method for the general degenerate case. This work is completed by analyzing a spectral representation for the two-baryon correlations and providing the leading behaviors of the field strength normalization and the mass of the spectral contributions with more than one-particle. These are needed results for a rigorous analysis of the two-baryon and meson-baryon particle spectra.
We present a calculation of the Hadron spectrum in the Dyson-Schwinger/Bethe-Salpeter approach to continuum QCD. A sophisticated truncation featuring all covariant structures of the quark-gluon vertex, with its inherent flavour dependence, is employed in a framework that preserves the dynamics of chiral symmetry breaking. The study is suggestive as to the relevance of additional resonant and non-resonant two- and three-body contributions.
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The existence of the cosmic neutrino background is a robust prediction of the hot big bang model. These neutrinos were a dominant component of the energy density in the early Universe and therefore played an important role in the evolution of cosmological perturbations. The energy density of the cosmic neutrino background has been measured using the abundances of light elements and the anisotropies of the cosmic microwave background. A complementary and more robust probe is provided by a distinct shift in the temporal phase of sound waves in the primordial plasma that is produced by fluctuations in the neutrino density. Here, we report on the first constraint on this neutrino-induced phase shift in the spectrum of baryon acoustic oscillations of the BOSS DR12 data. Constraining the acoustic scale using Planck data while marginalizing over the effects of neutrinos in the cosmic microwave background, we find a non-zero phase shift at greater than 95% confidence. Besides providing a new test of the cosmic neutrino background, our work is the first application of the baryon acoustic oscillation signal to early Universe physics.
Here, we describe a calculation of the spectrum of flavor-SU(3) octet and decuplet baryons, their parity partners, and the radial excitations of these systems, made using a symmetry-preserving treatment of a vector x vector contact interaction as the foundation for the relevant few-body equations. Dynamical chiral symmetry breaking generates nonpointlike diquarks within these baryons and hence, using the contact interaction, flavor-antitriplet scalar, pseudoscalar, vector, and flavor-sextet axial-vector quark-quark correlations can all play active roles. The model yields reasonable masses for all systems studied and Faddeev amplitudes for ground states and associated parity partners that sketch a realistic picture of their internal structure: ground-state, even-parity baryons are constituted, almost exclusively, from like-parity diquark correlations, but orbital angular momentum plays an important role in the rest-frame wave functions of odd-parity baryons, whose Faddeev amplitudes are dominated by odd-parity diquarks.
I describe recent progress at understanding the excited baryon spectrum of QCD from lattice gauge simulations. I begin by outlining the recipe for spectroscopy calculations. I compare lattice calculations of the spectrum of the baryons containing the light (u,d) and strange quarks for pion masses in excess of 400 MeV, and compare with expectations from QCD-inspired descriptions of the spectrum, before addressing the issue of unstable resonances in lattice QCD. I conclude by describing the prospects for examining the electromagnetic properties of baryon excited states from lattice gauge calculations.
The new CLAS12 large acceptance spectrometer was recently installed in Hall B as part of the 12 GeV upgrade project at Jefferson Laboratory that served to double the maximum electron beam energy of the accelerator. The approved CLAS12 experimental physics program spans a broad scientific scope designed to address fundamental and critical issues in nuclear physics such as detailed spectroscopy of the excited baryon spectrum including a search for hybrid baryons where the glue serves as an active structural component, elucidation of the role of gluons in hadronic structure, studies of the implications of short range forces acting in nucleons and nuclei, and detailed investigations that serve to reveal the structure of ground and excited states including 3-D imaging of the ground state nucleons and exploration of the N --> N* form factors in the transition from the regimes of confinement to perturbative QCD. These studies will address questions on the nature of the mass of hadrons, quark-gluon confinement, and how such a diversity of hadrons emerges from QCD. The commissioning of the CLAS12 spectrometer was completed during an Engineering Run that took place in Dec. 2017 and Jan. 2018. This was followed by the first physics production running periods spanning 23 weeks in the spring and fall of 2018. This talk will review the initial CLAS12 physics program and highlight the current status of the ongoing physics analyses. *The Southeastern Universities Research Association (SURA) operates the Thomas Jefferson National Accelerator Facility for the United States Department of Energy under Contract No. DE-AC05-84ER40150. This material is based upon work supported by the US Department of Energy, Office of Science, Office of Nuclear Physics under Contract No DE-AC05-06OR23177.
We present nonperturbative lattice calculations in the quenched approximation of the low-lying meson and baryon spectrum of the SU(4) gauge theory with fundamental fermion constituents. This theory is one instance of stealth dark matter, a class of strongly coupled theories, where the lowest mass stable baryon is the dark matter candidate. This work constitutes the first milestone in the program to study stealth dark matter self-interactions. Here, we focus on reducing excited state contamination in the single-baryon channel by applying the Laplacian Heaviside method, as well as projecting our baryon operators onto the irreducible representations of the octahedral group. We compare our resulting spectrum to previous work involving Gaussian smeared nonprojected operators and find good agreement with reduced statistical uncertainties. We also present the spectrum of the low-lying odd-parity baryons for the first time.
The nature of the {Lambda}(1405), and its place in the baryon spectrum has remained uncertain for decades. Theoretical studies have shown that it may possess strong dynamical components which are not seen in other well-known baryons. Using the CLAS detector system in Hall B at Jefferson Lab, we have measured the photoproduction reaction {gamma} + p {yields} K{sup +} {Lambda}(1405) with high statistics and over different {Sigma}{pi} decay channels. The reconstructed invariant mass distribution (lineshape) has been measured, as well as the differential cross sections for the {Lambda}(1405), {Sigma}(1385), and {Lambda}(1520). Our analysis method is discussed and our near-final results for the {Lambda}(1405) lineshape and differential cross section are presented.
Using a confining, symmetry-preserving regularization of a vector x vector contact interaction, we compute the spectra of ground-state pseudoscalar and vector of ($f$$\bar{g}$) mesons, scalar and axial-vector ($fg$) diquarks, and $J^{P}$ = 1/2(+), 3/2(+) ($fgh$) baryons, where $f, g, h$ is an element of {$u, d, s, c, b$}. The diquark correlations are essentially dynamical and play a key role in formulating and solving the three-valence-quark baryon problems. The baryon spectrum obtained from this largely algebraic approach reproduces the 22 known experimental masses with an accuracy of 2.9(2.4)%. It also possesses the richness of states typical of constituent-quark models, predicting many heavy-quark baryons not yet observed. This study indicates that diquark correlations are an important component of all baryons; and owing to the dynamical character of the diquarks, it is typically the lightest allowed diquark correlation that defines the most important component of a baryon's Faddeev amplitude.