Naive Quark Model Research Articles

The proton spin, axial vector current and mesonic cloud

We argue that the suppression of the nonsinglet axial vector couplings g A/ g V from the naive quark model value can easily be understood as an effect of the mesonic cloud around the proton. However, it does not seem possible to generate a sufficiently large polarization of the ss̄ sea needed to understand, within the naive parton model, the EMC data on the polarized structure function. Thus our results strengthen the arguments that the gluons in the proton contribute through the Adler-Bell-Jackiw anomaly to the EMC data.

Gluons and the spin of the proton

The recent observation that constituent quark helicities carry very little of the spin of the proton, in contrast with naive quark model expectations, can be understood by taking into account non-perturbative aspects of QCD, such as chiral symmetry breaking and confinement. We compute the non-strange quark contribution Δu+ Δd to the proton spin in a chiral field-theoretical model of quark and gluon confinement. Our mean field computations include self-consistently the effects of gluon exchange between constituent quarks. When the parameters of the model, including the effective strong fine structure constant α s, are adjusted to reproduce as far as possible the experimental mean nucleon-delta mass and the relative nucleon-delta mass splitting, we obtain Δu+Δd⋍0.26, which is only one third of the α s=0 value. We show that this implies that all the proton spin is in fact orbital angular momentum.

Updated constraints on axions from SN1987A

We recently determined a lower bound on the axion decay constant (upper bound on the axion mass) by demanding that the axion emission rate in SN1987A be small enough to be consistent with the observed neutrino emission. We estimate here the magnitude of corrections to our previous results due to high density effects, ϱ exchange and the restoration of chiral symmetry. Assuming a non-degenerate core, we now find that for naive quark model couplings f a ≳0.2×10 12 GeV( m a ≲3.6×10 −4 eV) which is a factor of 4 different from our previous limits assuming a degenerate core. Limits using couplings derived from EMC measurements are a factor of 2–4 weaker. We show that there is no window in f a for non-freely-streaming axions. These limits still imply that the remaining window for axions is the one which is the most interesting for cosmology.

Realistic predictions for the detection of supersymmetric dark matter

We present new predictions for the detection of supersymmetric dark matter via its annihilation in the Sun and elastic scattering off heavy nuclei in the laboratory. Our predictions include many effects found in realistic models such as non-degenerate left- and right-squark masses, unequal supersymmetric Higgs v.e.v.s and photino/higgsino/zino mixing in the lightest supersymmetric particle (LSP). Hadronic matrix elements are estimated using either the naive quark model or the EMC measurement of the spin-dependent proton structure function and perturbative QCD. Nuclear matrix elements are calculated using the shell-model and the small effects of quark vector current operators are discussed. Previous predictions for the elastic LSP-proton scattering cross section, and hence for high energy solar neutrinos from LSP annihilations, are reduced by the EMC estimate and by unequal squark masses, but may be increased by unequal Higgs v.e.v.s. Previous predictions for elastic photino scattering off nuclei with unpaired neutrons are greatly enhanced by the EMC estimate. As a result, preferences for the nuclei to be used in laboratory experiments to detect supersymmetric dark matter may be greatly altered.

Where is the decay ϱ' (1600) → ωπ 0?

It is shown that the existing experimental data on ϱ' (1600) → ωπ 0 and ϱ' (1600) → K ∗ K + K ∗K decays cannot be understood in the framework of the naive quark model. The study of these decays in e +e - annihilation is thought to be of great necessity and interest.

Static electromagnetic properties of baryons in the chiral soliton model and in the naive quark model for three flavors and an arbitrary number of colors.

We present calculations of magnetic moments and electromagnetic transition matrix elements of the ground-state baryons in the context of the chiral soliton model (in a semiclassical approximation) as well as of the naive quark model with an arbitrary number of colors N and three flavors. On comparing the results of these two models we find that they are in very good agreement with each other for all odd-integer values of the number of colors N (N\ensuremath{\ge}3). As regards the nonstrange baryons we find much better agreement of the two models in the case of three flavors than in the case of two flavors. The strong dependence of some of the results on the number of colors leads us to conclude that there is no justification for the usual procedure of comparing calculations for three colors with experimental data in order to support the validity of the 1/N expansion.

H dibaryon in the naive quark model with arbitrary Nc.

It is shown that the H dibaryon (a proposed \ensuremath{\Lambda}\ensuremath{\Lambda} bound state) is not bound in the naive quark model for ${N}_{c}$>3. Flavor-SU(3)-symmetry breaking is also discussed.

Two-body Dirac equations for particles interacting through world scalar and vector potentials.

In a recent Letter, we used ''two-body Dirac equations'' to make the naive quark model fully relativistic. In this paper, we apply Dirac's constraint mechanics and supersymmetry not to a string but instead to a system of two spinning particles to derive the two coupled Dirac equations that govern the quantum mechanics of two spin-1/2 particles interacting through world scalar and vector potentials. Along the way, we demonstrate that our equations are compatible, that the scalar and vector interaction structures contribute separately to compatibility when both are present, and that compatibility persists even in the presence of relative-momentum-dependent interactions. We show that extrapolation of supersymmetries associated with the ordinary single-particle Dirac equation to the interacting two-body system eliminates spin complications and reduces the compatibility problem to that of the corresponding spinless system. In addition, supersymmetry introduces physically important nonperturbative recoil effects that contribute to the correct perturbative spectrum while rendering nonsingular certain singular terms of standard semirelativistic approximations. This eliminates the need for singularity-softening parameters or finite particle sizes in phenomenological applications. In order to make clear the underlying structure of our equations, we also derive the corresponding coupled Dirac or Klein-Gordon equations that govern a system of two particles,more » one or neither of which has spin.« less

Quark potential model of baryon spin-orbit mass splittings

We show that it is possible to make the P-wave spin-orbit mass splittings in Λ baryons consistent with those of nonstrange baryons in a naive quark model, but only by introducing additional terms in the quark-quark effective interaction. These terms might be related to contributions due to pomeron exchange and sea excitations. The implications of our model in meson spectroscopy and nuclear forces are discussed.

Meson dynamics beyond the quark model: Study of final-state interactions.

A scalar glueball is predicted in the 1-GeV mass region. The present analysis is concerned with experimental evidence for such a state. It has been proposed that glueballs should be preferentially produced in supposedly glue-rich processes such as \ensuremath{\psi} decay and double-Pomeron exchange. However, any meson of such a mass and quantum number has very restricted decay channels available---essentially only \ensuremath{\pi}\ensuremath{\pi} and, if the mass allows, KK\ifmmode\bar\else\textasciimacron\fi{}. In this case, any production process is very tightly correlated to elastic reactions, \ensuremath{\pi}\ensuremath{\pi}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi} and \ensuremath{\pi}\ensuremath{\pi}\ensuremath{\rightarrow}KK\ifmmode\bar\else\textasciimacron\fi{}, by unitarity. Novel processes cannot then reveal effects that could not be seen in these elastic reactions. Nevertheless, they can valuably supplement this standard information where it lacks precision. Recent high-statistics results on central dimeson production at the CERN ISR enable us to perform an extensive new coupled-channel analysis of I=0 S-wave \ensuremath{\pi}\ensuremath{\pi} and KK\ifmmode\bar\else\textasciimacron\fi{} final states. This unambiguously reveals three resonances in the 1-GeV region, ${S}_{1}$(991), ${S}_{2}$(988), and \ensuremath{\epsilon}(900), where the naive quark model expects just two. We discuss in detail these new features and how they may be confirmed experimentally, and give their present interpretation. The ${S}_{1}$(991) is a plausible candidate for the scalar glueball. We examine other production reactions (heavy-flavor decays and \ensuremath{\gamma}\ensuremath{\gamma} reactions) leading to the same final states, and discuss how, with future precision, these can probe fine details.

Experimental evidence for dynamics beyond the quark model: An extra I = 0 scalar meson near 1 GeV

Incorporating new data on pp → ppππ(K K ), a coupled channel analysis of results on ππ, KK̄ final state interactions with I = 0 0 ++ quantum numbers below 1.6 GeV is performed. It is shown that though no poles are imposed on these data at least three and probably four distinct resonances emerge, when the naive quark model requires but two. This we claim constitutes definite evidence for new dynamics in the 0 ++ channel with gluonic modes in the wave function.

GA/GV in the quark model

It is shown that the naive nonrelativistic quark model, in the presence of pion emission and absorption, reproduces the usual Goldberger–Treiman relation for the nucleon axial–vector coupling constant.

Equivalence of the chiral soliton and quark models in large N

We prove that the group theoretic structure of the chiral soliton model is identical to that of the naive quark model in the large- N C limit. This implies that all group theoretic calculations such as the F D ratios, g πNN g πNΔ , etc. are identical in the soliton and quark models in large N. This result is true for an arbitrary number of flavors. We also compare the two models for finite N C .

Weakly model dependent pion form factor with physically interpretable parameters

We have constructed the pion form factor model satisfying fundamental principles, providing some freedom for the asymptotic behaviour and depending only on the adjustable parameters with a definite physical interpretation. The explicit incorporation of the pion form factor left-hand cut from the second Riemann sheet into a model was carried out for the first time. As a result we have described (contrary to the previous attempts [18, 19]) the pion form factor data from the range of momenta −9·770 GeV2 ≦t ≦ 9·579 GeV2 and data on theP-wave isovectorππ phase shift in the elastic region simultaneously with the adjustable parameters acquiring very reasonable values. The asymptotic behaviour was enforced by the data to be consistent with the naive quark model prediction. The calculated values of the pion charge radius as well as theP-wave isovectorππ scattering length coincide with the world averaged values. With regard to these positive features of our pion form factor model it can be employed for the reliable calculation (via unitarity) of theP-wave isovectorππ scattering partial amplitude outside the physical region, which could be useful in a saturation of various sum rules inππ scattering physics.

Relativistic Naive Quark Model for Spinning Quarks in Mesons

We use two-body Dirac equations (derived from Dirac's constraint mechanics and super-symmetry) to make the naive quark model fully relativistic. Our covariant equations incorporate not only relativistic kinematics but also dynamical recoil effects that generalize Breit corrections to forms that have well-defined quantum short-distance behavior. In these equations, a crude but covariant generalization of Richardson's static quark potential produces a surprisingly good one-parameter relativistic fit to the meson spectrum.

Naive quark model for an arbitrary number of colors

Naive quark model for an arbitrary number of colors

Quark axial coupling quenching and nucleon coupling constants

Abstract The nucleon axial and pion-nucleon isobar coupling constants are calculated in a non-relativistic quark model for baryons with a pion cloud. We emphasized in this letter one possible way by which the experimental values are reproduced, namely the quenching of the quark axial coupling constant. This mechanism is consistent with the traditional naive quark model approach.

Semileptonic decays ofBmesons

We have studied the production of B mesons in e/sup +/e/sup -/ annihilations and present new measurements of the semileptonic branching fractions for B-meson decay. We find B(B..-->..e..nu..X) = 0.127 +- 0.017 +- 0.013 and B(B..--> mu nu..X) = 0.122 +- 0.017 +- 0.031, where the errors are statistical and systematic, respectively. The observed lepton momentum spectra from B decays are presented. From these spectra we find the mean hadronic mass (M/sub X/) recoiling against the detected lepton to be M/sub X/ = 2.2 +- 0.2 GeV/c/sup 2/. We have also observed an enhancement in the lepton yield from the continuum above BB-bar threshold. This enhancement is interpreted as continuum B production and is consistent with what is expected from the naive quark model.

Incorporating pion effects into the naive quark model

A hybrid of the naive nonrelativistic quark model and the Chew-Low model is proposed. The pion is treated as an elementary particle which interacts with the "bare baryon" or "baryon core" via the Chew-Low interaction. The baryon core, which is the source of the pion interaction, is described by the naive nonrelativistic quark model. It turns out that the baryon-core radius has to be as large as 0.8 fm, and consequently the cutoff momentum $\ensuremath{\Lambda}$ for the pion interaction is $\ensuremath{\lesssim}3{m}_{\ensuremath{\pi}}$, ${m}_{\ensuremath{\pi}}$ being the pion mass. Because of this small $\ensuremath{\Lambda}$ (as compared with $\ensuremath{\Lambda}\ensuremath{\sim}\mathrm{nucleon}$ mass in the old Chew-Low model) the effects of the pion cloud are strongly suppressed. The baryon masses, baryon magnetic moments (except for ${\ensuremath{\Xi}}^{\ensuremath{-}}$), and the nucleon charge radii can be reproduced quite well. However, we found it singularly difficult to fit the axial-vector weak decay constant ${g}_{A}$.

Gluons in the hadronicS matrix

We derive a theoretical explanation of the similarities which have been experimentally observed between final state distributions in soft processes (K−p interactions andpp collisions at ISR) and hard processes (e+e− annihilations and deep inelastic scattering). The theoretical framework is the correspondence between QCD and dual topological unitarization (DTU), which expresses confinement as the equivalence of the hadron and parton bases to account for unitarity. Starting from the interpretation of the zero handle topology in DTU in terms of the naive quark parton model, we show how to characterize gluons in the hadron basis: primordial gluons are associated with the one handle topology, and the cascading of hard gluons is related to the sum of all higher topologies in DTU. We get this way a QCD interpretation of the reggeon calculus which is the theoretical framework of soft hadronic processes at asymptotic energies.