Negative Parity Baryons Research Articles

Sextet string tension, mock baryonia and theU(3.1) resonance

We investigate the potential between static color sextet sources, a topic of central importance in connection with the existence or non-existence of mock-baryonia. The result is that these states should exist. We derive an effective potential for diquarks and discuss features ofT- andM-baryonia which may help to clarify the nature of theU(3.1) in forthcoming experiments. The suggested decay mechanism predicts that decays into Λ $$\bar p$$ plus pions prefer to proceed via the negative parity baryon resonances.

Nonleptonic hyperon decays-wave amplitudes and negative-parity excited baryons

The contribution of negative-parity excited baryons is calculated and found to be small relative to other contributions (i.e. the equal-time commutator and the vector-meson pole) which have been successfully employed in the recent past. While positive-parity excited baryons help to explainp-wave (B) amplitudes, 1/2− baryon poles do not spoil the existing description ofs-wave (A) amplitudes.

Ground-state andP-wave charmed baryons in a consistent quark model with hyperfine interactions

Masses of the various ground-state and negative-parity baryons containing one charmed quark are calculated using a parameter set developed for the noncharmed baryons. The sole additional parameter needed, ${m}_{c}$, is obtained by fitting to the observed mass of ${\ensuremath{\Lambda}}_{c}{\frac{1}{2}}^{+}$. The resulting calculated value of the mass of ${\ensuremath{\Sigma}}_{c}{\frac{1}{2}}^{+}$ is in reasonable agreement with experimental values.

Analysis of splitting mechanisms in the low-lying non-strange negative-parity baryons

We investigate the mass splitting in the negative parity N ∗ and Δ ∗ spectrum where, experimentally, the spin-orbit force is found to be highly suppressed. A hyperfine interaction between quarks derived from a one-gluon and one-pion exchange model for a spherical chiral bag is used. The interaction is, unlike the usual Fermi-Breit force, fully relativistic and explicitly takes into account confinement effects. We analyze in detail how the force operates in the odd parity N ∗ and Δ ∗ spectrum and find that the suppression of spin-orbit forces, which is mysterious in constituent quark models, can be explained.

P-wave baryons in a consistent quark model with hyperfine interactions

Masses of the various negative-parity baryons are calculated using a single consistent parameter set as described by Kalman and Hall. Reasonable fits to the masses of most of the ground-state and negative-parity baryons are obtained.

Penguins and the parity-violating Ω − → Ξ −γ and Ξ − → Σ −γ modes

The Ω − → Ξ −γandΞ − → Σ −γ decays are analyzed in a non-relativistic quark model with negative parity baryons as intermediate states, the latter being uniquely specified by exact weak and e.m. “selection rules”. Ω − → Ξ −γ, for which an upper limit on the branching ratio (< 3.1 × 10 −3) was recently reported by Bourquin et al., is found to hold promise as the best choice for the estimation of the magnitude of the Wilson coefficients for the penguin contributions in the QCD corrected non-leptonic hamiltonian.

Consistent quark model with hyperfine interactions for the ground and low-lying excited baryon states

Isgur and Karl have recently analyzed the ground and low-lying excited baryon states; the negative-parity and positive-parity baryons are treated separately using different parameter sets. In this paper we show how the Hamiltonian introduced by Isgur and Karl to examine the positive-parity baryons can be modified to apply to the negative-parity baryons. In particular, the mass difference between ..lambda..5/2/sup -/ and ..sigma..5/2/sup -/ is restored to a value consistent with experiment.

Hyperfine interactions in negative parity baryons and the ΔD35(1925) resonance

We investigate the mass and composition of the ΔD35(1925) resonance within the framework of the Isgur-Karl model. After inclusion of hyperfine effects, and with reasonable values of the parameters in the model, we find good agreement with the results of a recent phase-shift analysis by Cutkosky et al.

P-wave baryons in the quark model

We discuss the spectrum and mixing angles of negative-parity baryons in a quark-model framework inspired by quantum chromodynamics. We take into account in zero order the removal of the degeneracy between the two $P$-wave states of the three-quark system in the $S=\ensuremath{-}1$ sector, as well as the hyperfine interaction between quarks, but neglect spin-orbit coupling. We find good agreement with experiment in the $S=0$ and $S=\ensuremath{-}1$ sectors where there are data and predict the $S=\ensuremath{-}2, \ensuremath{-}3$ sectors.

Hyperfine interactions in negative parity baryons

The hyperfine interaction between quarks suggested in chromodynamics can, without free parameters, explain the size and pattern of the splittings and the mixing angles observed experimentally in nonstrange, negative parity baryons.

An su (6) w fit to the negative parity baryon decay rates

We present a least squares fit to the experimental data on decays of negative parity baryon resonances into a pseudoscalar meson and either a J P = 1/2 + stable baryon or a J P = 3/2 + decuplet member. We find that the s-waves and d-waves are separately in good agreement with the predictions of SU (6) w ⊗ O(2) L z . Predictions are given regarding several as yet unobserved decay processes, and for those which concern hitherto undetected resonances, their possible detection is discussed.

Extension of the Mass Operator in the Symmetric Quark Model for Negative-Parity Baryon Resonances

Extension of the Mass Operator in the Symmetric Quark Model for Negative-Parity Baryon Resonances

Formation and decay of negative-parity baryon resonances in a brokenU 6,6 model

Formation and decay of negative-parity baryon resonances in a brokenU 6,6 model

Reanalysis of the Lowest-Mass Negative-Parity Baryon Resonances Using the Symmetric Quark Model

Reanalysis of the Lowest-Mass Negative-Parity Baryon Resonances Using the Symmetric Quark Model

The SU(3) structure of negative-parity baryon states

It is argued that our present knowledge of the negative-parity baryon mass spectrum is consistent with the simplest possible assumptions concerning their SU(3) structure. Some relatively exact statements can therefore be made concerning the masses which are amenable to immediate experimental tests. The more complex questions of decay, decay sum rules, and mixing, are then examined in the general framework of the simplified assumptions.

Negative parity baryon resonances in the SU(6) symmetry

The decay ratios of negative parity baryon resonances are compared with prediction of SU W (6) symmetry by assigning these resonances to the 540 supermultiplet. Some “semiempirical” mass formulae are also investigated. It turns out that the present experimental data are not inconsistent with such an assignment. Nevertheless, we believe that not all the negative parity baryon resonances of spins 1/2−, 3/2−, 5/2− fit into the 540-plet without contradicting experimental values.

Model of Positive-Parity Baryon Excited States

The occurrence in nature of very high-spin baryons leads to the suggestion that they can be described as composites of high-spin baryons and mesons with low orbital angular momentum. As a consequence, there appears to be no limit beyond which the baryon spectrum cannot extend. We implement these ideas with a dynamical bootstrap model of positive-parity baryons employing $\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}O(3)$ symmetry. We prove the consistency of this symmetry with our dynamics, and predict a spectrum in accord with the latest phase-shift analysis of the pion-nucleon system. We indicate how our model is described in a Regge theory of angular momentum trajectories, and we conclude with a comment on the negative-parity baryon spectrum.

Baryon Mass Splittings in anSU(6)×O(3)Quark Model

The positive- and negative-parity baryon mass shifts are investigated under the assumption that these particles belong, respectively, to the representations (56,1) and (70,3) of the group $\mathrm{SU}(6)\ifmmode\times\else\texttimes\fi{}O(3)$, which are dynamically realizable from a 3-quark model with totally symmetric ($S$) functions, as found earlier by one of the authors. Two different types of $\mathrm{SU}(2)$-invariant central forces ${V}^{(1)}$ and ${V}^{(2)}$, each of which is shown to be in conformity with the usual mass relations for the 56 states, are employed. One of these forces (${V}^{(2)}$) is, however, found to violate the Gell-Mann-Okubo formula for certain negative-parity octets. It is also found that appreciable mixtures of both ${V}^{(1)}$ and ${V}^{(2)}$ are necessary even for a qualitative representation of the experimental masses. The effect of an $\mathrm{SU}(2)$-invariant spin-orbit force of the type ${\ensuremath{\tau}}_{1}\ensuremath{-}{\ensuremath{\tau}}_{2}$ of modest strength (\ensuremath{\sim}25 MeV) is found to be very helpful in producing a reasonably good fit to the actual masses of the negative-parity baryons. Such a force has, however, no first-order effect on the 56 masses, on the assumption of orbital $S$ functions, which can be constructed only with $S$-wave $Q\ensuremath{-}Q$ pairs. The significance of this result is briefly discussed in connection with the question of quark statistics.

Quark Model for Baryon-Baryon Processes

A quark ($Q$) model recently proposed by the authors for high-energy meson-baryon and photoproduction processes is extended to high-energy baryon-baryon scattering and production of negative-parity baryons. The positive- and negative-parity baryons are assumed to belong, respectively, to the representations (56,1) and (70,3) of the group $\mathrm{SU}(6)\ifmmode\times\else\texttimes\fi{}O(3)$. Sum rules resembling those of $\mathrm{SU}(3)$ and $\mathrm{SU}(6,6)$, but differing in details, are obtained for the baryon-baryon processes within the 56 representation. An interesting sum rule which is obtained for negative-parity baryon production involves only nonstrange particles and could be within fairly early reach of experiment. The model is primarily characterized by an impluse approximation for $Q\ensuremath{-}Q$ scattering and thus disallows processes involving exchanges of more than one unit of charge, hypercharge, and even spatial symmetry, among the initial and final $3Q$ states representing the baryons. This last condition precludes the high-energy peripheral production of metastable baryon states like the Roper resonance, which we believe to have an internal orbital structure of ${L}^{P}={1}^{+}$.

Paraquark dynamics of baryons and resonances

A three-body formalism, within a non-relativistic quark ( Q) model, is developed for a dynamical treatment of baryons and their resonances as bound 3 Q-systems, via Q- Q interactions operating through a Schrödinger equation, with all degrees of freedom (space, spin and unitary spin) taken into account. The main assumptions are (i) parastatistics and (ii) operation of Q- Q forces in s- and p-waves only. A detailed classification of the various 3 Q-states of the correct symmetry is obtained in terms of (LSJ) assignments as well as SU(3) multiplet structures, using the symmetric ( S), antisymmetric ( A), and mixed ( M) representations of the permutation group of three objects. The Schrödinger equations for the spatial parts of the 3 Q-wavefunctions are found to separate into those for S, M, and A types for different values of L, in the limit of “full degeneracy” represented by spin and SU (3)-spin-independent Q- Q potentials in s- and p-waves. The group structures generated by these equations are precisely those of SU(6) ⊗ O(3). The further assumption of separable forms for the potentials, leads to coupled one-dimensional equations for certain “spectator functions” associated with the spatial wavefunctions. For the s-wave force which strongly generates even-parity ( L = 0) states, and only weak L P = 1 − states, these kernels are attractive for S, but repulsive for M functions of L P = 0 +. The p-wave interaction, on the other hand, strongly generates both even- and odd-parity states. For L P = 1 − states, M and A functions have attractive and repulsive kernels, respectively. The opposite holds for even-parity states, with A functions of L P = 1 +and 0 + having attractive and repulsive kernels, respectively. A p-wave spin-orbit force is incorporated in the formalism and shown to break up the supermultiplets into SU(3) multiplets for which approximate but explicit mass formulas are derived. The main results of experimental interest are the following: 1. (i) A dynamical realization of the 56 states of baryons via S-functions of L P = 0 +. 2. (ii) A ( 70, 3) representation of SU(6) ⊗ (3), via M-functions of L P = 1 − of the negative parity baryon states whose SU(3) multiplet structure is in qualitative accord with Dalitz' analysis of experimental data. 3. (iii) A ( 20, 3) representation for L P = 1 + states of which the lowest lying ones are an octet and a singlet, each of J P = 1 2 + , thus providing a dynamical explanation of the “Roper” resonance and predicting a new singlet in the “low”-mass region.