Baryon States Research Articles

Observation of charmless baryonic decays B(s)0→pp¯h+h′−

Decays of $B^0$ and $B_{s}^0$ mesons to the charmless baryonic final states $p \overline{p} h^+ h^{\prime-}$, where $h$ and $h^\prime$ each denote a kaon or a pion, are searched for using the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies of $7$ and $8\,$TeV, corresponding to an integrated luminosity of $3\,$fb$^{-1}$. Four-body charmless baryonic $B_{s}^0$ decays are observed for the first time. The decays $B^0_{s}\to p \overline{p} K^+ K^-$, $B^0_{s}\to p \overline{p} K^\pm \pi^\mp$, $B^0\to p \overline{p} K^\pm \pi^\mp$ and $B^0\to p \overline{p} \pi^+\pi^-$ are observed with a significance greater than $5$ standard deviations; evidence at $4.1$ standard deviations is found for the $B^0\to p \overline{p} K^+ K^-$ decay and an upper limit is set on the branching fraction for $B^0_{s}\to p \overline{p} \pi^+ \pi^-$. Branching fractions in the kinematic region $m(p \overline{p})<2850\,$MeV$/c^2$ are measured relative to the $B^0 \to J/\psi (\to p \overline{p}) K^*(892)^0$ channel.

Asymmetric dark matter and the hadronic spectra of hidden QCD

The idea that dark matter may be a composite state of a hidden nonabelian gauge sector has received great attention in recent years. Frameworks such as asymmetric dark matter motivate the idea that dark matter may have similar mass to the proton, while mirror matter and $G \times G$ grand unified theories provide rationales for additional gauge sectors which may have minimal interactions with standard model particles. In this work we explore the hadronic spectra that these dark QCD models can allow. The effects of the number of light colored particles and the value of the confinement scale on the lightest stable state, the dark matter candidate, are examined in the hyperspherical constituent quark model for baryonic and mesonic states.

Decay chain information on the newly discovered double charm baryon state Ξcc++

We interprete the new double charm baryon state found by the LHCb Collaboration in the invariant mass distribution of the set of final state particles $(\Lambda_c^+\,K^-\,\pi^+\,\pi^+)$ as being at the origin of the decay chain $\Xi_{cc}^{++} \to \Sigma_c^{++} (\to \Lambda_c^+ \pi^+) +\bar K^{*0} (\to K^- \pi^+)$. The nonleptonic decay $\Xi_{cc}^{++} \to \Sigma_c^{++} + \bar K^{*0}$ belongs to a class of decays where the quark flavor composition is such that the decay proceeds solely via the factorizing contribution precluding a contamination from internal $W$-exchange. We use the covariant confined quark model previously developed by us to calculate the four helicity amplitudes that describe the dynamics of the transition $\Xi_{cc}^{++} \to \Sigma_c^{++}$ induced by the effective $(c \to u)$ current. We then proceed to calculate the rate of the decay as well as the polarization of the $\Sigma_c^{++}$ and $\Lambda_c^+$ baryons and the longitudinal/transverse composition of the $\bar K^{*0}$. We estimate the decay $\Xi_{cc}^{++} \to \Sigma_c^{++} \bar K^{*0}$ to have a branching rate of $B(\Xi_{cc}^{++} \to \Sigma_c^{++} \bar K^{*0}) \sim 10.5 \%$. As a byproduct of our investigation we have also analyzed the decay $\Xi_{cc}^{++} \to \Sigma_c^{++} \bar K^{0}$ for which we find a branching ratio of $B(\Xi_{cc}^{++} \to \Sigma_c^{++} \bar K^0) \sim 2.5 \%$.

Regge trajectories of excited baryons, quark-diquark models, and quark-hadron duality

The parton model relations in conjunction with quark-hadron duality in deep inelastic scattering suggests an asymptotic dominance of quark-diquark type of baryonic excited states with a radial Regge uniformly distributed mass squared spectrum $M_{n}^2 = \mu^2 n + M_0^2$. We argue that this points to a lineary quark-diquark confining potential. We analyze the radial ($n$) and angular-momentum ($J$) Regge trajectories for all light-quark states with baryon number one listed in the 2016 edition of the Particle Data Tables. The parameters of the mass squared trajectories are obtained by linear regression assuming $\Delta M_n^2 \sim M_n \Gamma_n $ weighted with the width $\Gamma_n$ of the resonance and the error analysis is carried out accordingly.

Spectra of charmed and bottom baryons with hyperfine interaction**Supported by National Natural Science Foundation of China (11175020, 11575023, U1204115)

Up to now, the excited charmed and bottom baryon states have still not been well studied experimentally or theoretically. In this paper, we predict the mass of , the only L = 0 baryon state which has not been observed, to be 6069.2 MeV. The spectra of charmed and bottom baryons with the orbital angular momentum L = 1 are studied in two popular constituent quark models, the Goldstone boson exchange (GBE) model and the one gluon exchange (OGE) hyperfine interaction model. Inserting the latest experimental data from the “Review of Particle Physics", we find that in the GBE model, there exist some multiplets (Σc(b), and Ωc(b)) in which the total spin of the three quarks in their lowest energy states is 3/2, but in the OGE model there is no such phenomenon. This is the most important difference between the GBE and OGE models. These results can be tested in the near future. We suggest more efforts to study the excited charmed and bottom baryons both theoretically and experimentally, not only for the abundance of baryon spectra, but also for determining which hyperfine interaction model best describes nature.

Three-baryon interaction generated by determinant interaction of quarks

We discuss the three-baryon interaction generated by the determinant interaction of quarks, known as the Kobayashi-Maskawa-'t Hooft (KMT) interaction. The expectation value of the KMT interaction operator is calculated in fully-antisymmetrized quark-cluster model wave functions for one-, two- and three-octet baryon states. The three-baryon potential from the KMT interaction is found to be repulsive for $NN\Lambda$ and $N\Lambda\Lambda$ systems, while it is zero for the $NNN$ system. The strength and range of the three-baryon potential are found to be comparable to those for the $NNN$ three-body potential obtained in lattice QCD simulations. The contribution to the $\Lambda$ single particle potential in nuclear matter is found to be 0.28 MeV and 0.73 MeV in neutron matter and symmetric nuclear matter at normal nuclear density, respectively. These repulsive forces are not enough to solve the hyperon puzzle, but may be measured in high-precision hyperisotope experiments.

Peripheral transverse densities of the baryon octet from chiral effective field theory and dispersion analysis

The baryon electromagnetic form factors are expressed in terms of two-dimensional densities describing the distribution of charge and magnetization in transverse space at fixed light-front time. We calculate the transverse densities of the spin-1/2 flavor-octet baryons at peripheral distances b=O(Mπ−1) using methods of relativistic chiral effective field theory (χEFT) and dispersion analysis. The densities are represented as dispersive integrals over the imaginary parts of the form factors in the timelike region (spectral functions). The isovector spectral functions on the two-pion cut t>4Mπ2 are calculated using relativistic χEFT including octet and decuplet baryons. The χEFT calculations are extended into the ρ meson mass region using an N/D method that incorporates the pion electromagnetic form factor data. The isoscalar spectral functions are modeled by vector meson poles. We compute the peripheral charge and magnetization densities in the octet baryon states, estimate the uncertainties, and determine the quark flavor decomposition. The approach can be extended to baryon form factors of other operators and the moments of generalized parton distributions.

Magnetic moments and electromagnetic form factors of the decuplet baryons in chiral perturbation theory

We have systematically investigated the magnetic moments and magnetic form factors of the decuplet baryons to the next-to-next-leading order in the framework of the heavy baryon chiral perturbation theory. Our calculation includes the contributions from both the intermediate decuplet and octet baryon states in the loops. We also calculate the charge and magnetic dipole form factors of the decuplet baryons. Our results may be useful to the chiral extrapolation of the lattice simulations of the decuplet electromagnetic properties.

Radial excitations of the decuplet baryons

The ground and first excited states of the decuplet baryons are studied using the two-point QCD sum rule approach. The mass and residue of these states are computed and compared with the existing experimental data and other theoretical predictions. The results for the masses of the ground state particles as well as the excited Delta and Sigma ^{*} states are in good consistency with experimental data. Our results on the excited Xi ^{*} and Omega ^{-} states reveal that the experimentally poorly known Xi (1950) and Omega ^{-}(2250) can be assigned to the first excited states in Xi ^{*} and Omega ^{-} channels, respectively.

Pc(4380) in a constituent quark model

The constituent quark model with color-spin hyperfine potential is used to investigate the property of a compact pentaquark configuration with $J^p$=$3/2^-$ and isospin=1/2, which is the most likely quantum number of one of the recently observed exotic baryon states at LHCb. Starting from the characterization of the isospin, color, and spin states for the pentaquark configuration, we construct the total wave function composed of the spatial wave function, which we take to be symmetric and in S-wave, and the four orthogonal isospin $\otimes$ color $\otimes$ spin states that satisfy the Pauli principle. We then use the variational method to find a compact stable configuration. While there are compact configurations where the hyperfine potential is more attractive than the sum of $p$ and $J/\psi$ hyperfine potentials, we find that the ground state is the isolated $p$ and $J/\psi$ state. Furthermore, the mass of the excited state lies far above the observed pentaquark state leading us to conclude that the observed states can not be a compact multiquark configuration with $J^p$=$3/2^-$.

Low-lying charmed and charmed-strange baryon states

In this work, we systematically study the mass spectra and strong decays of 1P and 2S charmed and charmed-strange baryons in the framework of non-relativistic constituent quark models. With the light quark cluster–heavy quark picture, the masses are simply calculated by a potential model. The strong decays are studied by the Eichten–Hill–Quigg decay formula. Masses and decay properties of the well-established 1S and 1P states can be reproduced by our method. Sigma _c(2800)^{0,+,++} can be assigned as a Sigma _{c2}(3/2^-) or Sigma _{c2}(5/2^-) state. We prefer to interpret the signal Sigma _c(2850)^0 as a 2S(1/2^+) state although at present we cannot thoroughly exclude the possibility that this is the same state as Sigma _c(2800)^0. Lambda _c(2765)^+ or Sigma _c(2765)^+ could be explained as the Lambda _c^+(2S) state or Sigma ^+_{c1}(1/2^-) state, respectively. We propose to measure the branching ratio of mathcal {B}(Sigma _c(2455)pi )/mathcal {B}(Sigma _c(2520)pi ) in the future, which may disentangle the puzzle of this state. Our results support Xi _c(2980)^{0,+} as the first radial excited state of Xi _c(2470)^{0,+} with J^P=1/2^+. The assignment of Xi _c(2930)^0 is analogous to Sigma _c(2800)^{0,+,++}, i.e., a Xi ^prime _{c2}(3/2^-) or Xi ^prime _{c2}(5/2^-) state. In addition, we predict some typical ratios among partial decay widths, which are valuable for experimental search for these missing charmed and charmed-strange baryons.

Spectrum and Structure of Excited Baryons with CLAS*

In this contribution we discuss recent results in light quark baryon spectroscopy involving CLAS data and higher level analysis results from the partial wave analysis by the Bonn-Gatchina group. New baryon states were discovered largely based on the open strangeness production channels $\gamma p \to K^+ \Lambda$ and $\gamma p \to K^+ \Sigma^0$. The data illustrate the great potential of the kaon-hyperon channel in the discovery of higher mass baryon resonances in s-channel production. Other channels with discovery potential, such as $\gamma p \to p \omega$ and $\gamma p \to \phi p$ are also discussed. In the second part I will demonstrate on data the sensitivity of meson electroproduction to expose the active degrees of freedom underlying resonance transitions as a function of the probed distance scale. For several of the prominent excited states in the lower mass range the short distance behavior is described by a core of three dressed-quarks with running quark mass, and meson-baryon contributions make up significant parts of the excitation strength at large distances. Finally, an outlook is given of baryon resonance physics at the 12 GeV CEBAF electron accelerator.

First observation of the rare purely baryonic decay $B^0 \to p\overline{p}$

The first observation of the decay of a $B^0$ meson to a purely baryonic final state, $B^0 \to p\overline{p}$, is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb$^{−1}$. The branching fraction is determined to be $\mathcal{B}(B^0 \to p\overline{p}) = (1.25 \pm 0.27 \pm 0.18) \times 10^{−8}$, where the first uncertainty is statistical and the second systematic. The decay mode $B^0 \to p\overline{p}$ is the rarest decay of the $B^0$ meson observed to date. The decay $B^0_s \to p\overline{p}$ is also investigated. No signal is seen and the upper limit $\mathcal{B}(B^0 \to p\overline{p}) < 1.5 \times 10^{−8}$ at 90% confidence level is set on the branching fraction.

Towards a theoretical description of dense QCD

The properties of matter at finite baryon densities play an important role for the astrophysics of compact stars as well as for heavy ion collisions or the description of nuclear matter. Because of the sign problem of the quark determinant, lattice QCD cannot be simulated by standard Monte Carlo at finite baryon densities. I review alternative attempts to treat dense QCD with an effective lattice theory derived by analytic strong coupling and hopping expansions, which close to the continuum is valid for heavy quarks only, but shows all qualitative features of nuclear physics emerging from QCD. In particular, the nuclear liquid gas transition and an equation of state for baryons can be calculated directly from QCD. A second effective theory based on strong coupling methods permits studies of the phase diagram in the chiral limit on coarse lattices.

Flavor structure of Λ baryons from lattice QCD: From strange to charm quarks

We study $\mathrm{\ensuremath{\Lambda}}$ baryons of spin-parity ${\frac{1}{2}}^{\ifmmode\pm\else\textpm\fi{}}$ with either a strange or charm valence quark in full $2+1$ flavor lattice QCD. Multiple $SU(3)$ singlet and octet operators are employed to generate the desired single baryon states on the lattice. Via the variational method, the couplings of these states to the different operators provide information about the flavor structure of the $\mathrm{\ensuremath{\Lambda}}$ baryons. We make use of the gauge configurations of the PACS-CS Collaboration and chirally extrapolate the results for the masses and $SU(3)$ flavor components to the physical point. We furthermore gradually change the hopping parameter of the heaviest quark from strange to charm to study how the properties of the $\mathrm{\ensuremath{\Lambda}}$ baryons evolve as a function of the heavy quark mass. It is found that the baryon energy levels increase almost linearly with the quark mass. Meanwhile, the flavor structure of most of the states remains stable, with the exception of the lowest ${\frac{1}{2}}^{\ensuremath{-}}$ state, which changes from a flavor singlet $\mathrm{\ensuremath{\Lambda}}$ to a ${\mathrm{\ensuremath{\Lambda}}}_{c}$ state with singlet and octet components of comparable size. Finally, we discuss whether our findings can be interpreted with the help of a simple quark model and find that the negative-parity ${\mathrm{\ensuremath{\Lambda}}}_{c}$ states can be naturally explained as diquark excitations of the light $u$ and $d$ quarks. On the other hand, the quark-model picture does not appear to be adequate for the negative-parity $\mathrm{\ensuremath{\Lambda}}$ states, suggesting the importance of other degrees of freedom to describe them.

Vertex operators for production of baryon resonances in nucleon-gamma collisions with preserving gauge invariance and analyticity

Vertex operators for photo- and electro-production of baryon states with arbitrary spin-parity, [Formula: see text], are constructed. The operators obey gauge invariance and analyticity constraints. Analyticity is realized as a requirement of the generalized Siegert theorem for vertex form factors.

Skyrme model study of proton and neutron properties in a strong magnetic field

The proton and neutron properties in a uniform magnetic field are investigated. The Gell–Mann–Nishijima formula is shown to be satisfied for baryon states. It is found that with increasing magnetic field strength, the proton mass first decreases and then increases, while the neutron mass always increases. The ratio between magnetic moment of proton and neutron increases with the increase of the magnetic field strength. With increasing magnetic field strength, the size of proton first increases and then decreases, while the size of neutron always decreases. The present analysis implies that in the core part of the magnetar, the equation of state depend on the magnetic field, which modifies the mass limit of the magnetar.

Magnetic moments of the hidden-charm pentaquark states

The magnetic moment of a baryon state is an equally important dynamical observable as its mass, which encodes crucial information of its underlying structure. According to the different color-flavor structure, we have calculated the magnetic moments of the hidden-charm pentaquark states with $J^P={\frac{1}{2}}^{\pm}$, ${\frac{3}{2}}^{\pm}$, ${\frac{5}{2}}^{\pm}$ and ${\frac{7}{2}}^{+}$ in the molecular model, the diquark-triquark model and the diquark-diquark-antiquark model respectively. Although a good description for the pentaquark mass spectrum and decay patterns has been obtained in all the three models, different color-flavor structures lead to different magnetic moments, which can be used to pin down their inner structures and distinguish various models.

Searching for hidden-charm baryonium signals in QCD sum rules

We give an explicit QCD sum rule investigation to hidden-charm baryonium states with the quark content $u\bar u d\bar d c\bar c$, spin $J=0/1/2/3$, and of both positive and negative parities. We systematically construct the relevant local hidden-charm baryonium interpolating currents, which can actually couple to various structures, including hidden-charm baryonium states, charmonium states plus two pions, and hidden-charm tetraquark states plus one pion, etc. We do not know which structure these currents couple to at the beginning, but after sum rule analyses we can obtain some information. We find some of them can couple to hidden-charm baryonium states, using which we evaluate the masses of the lowest-lying hidden-charm baryonium states with quantum numbers $J^P=2^-/3^-/0^+/1^+/2^+$ to be around 5.0 GeV. We suggest to search for hidden-charm baryonium states, especially the one of $J=3^-$, in the $D$-wave $J/\psi \pi \pi$ and $P$-wave $J/\psi \rho$ and $J/\psi \omega$ channels in this energy region.

Testing a possible way of geometrization of the strong interaction by a Kaluza–Klein star

Geometrization of the fundamental interactions has been extensively studied during the century. The idea of introducing compactified spatial dimensions originated by Kaluza and Klein. Following their approach, several model were built representing quantum numbers (e.g. charges) as compactified space-time dimensions. Such geometrized theoretical descriptions of the fundamental interactions might lead us to get closer to the unification of the principle theories. Here, we apply a [Formula: see text] dimensional theory, which contains one extra compactified spatial dimension [Formula: see text] in connection with the flavor quantum number in Quantum Chromodynamics. Within our model the size of the [Formula: see text] dimension is proportional to the inverse mass-difference of the first low-mass baryon states. We used this phenomena to apply in a compact star model — a natural laboratory for testing the theory of strong interaction and the gravitational theory in parallel. Our aim is to test the modification of the measurable macroscopical parameters of a compact Kaluza–Klein star by varying the size of the compactified extra dimension. Since larger the [Formula: see text] the smaller the mass difference between the first spokes of the Kaluza–Klein ladder resulting smaller-mass stars. Using the Tolman–Oppenheimer–Volkov equation, we investigate the [Formula: see text]-[Formula: see text] diagram and the dependence of the maximum mass of compact stars. Besides testing the validity of our model we compare our results to the existing observational data of pulsar properties for constraints.