Showing papers on "Parton published in 1975"

Heavy Quarks and Strong Binding: A Field Theory of Hadron Structure

Abstract: We investigate in canonical field theory the possibility that quarks may exist in isolation as very heavy particles, ${M}_{\mathrm{quark}}gg1$ GeV, yet form strongly bound hadronic states, ${M}_{\mathrm{hadron}}\ensuremath{\sim}1$ GeV. In a model with spin-\textonehalf{} quarks coupled to scalar gluons we find that a mechanism exists for the formation of bound states which are much lighter than the free constituents. Following Nambu, we introduce a color interaction mediated by gauge vector mesons to quarantee that all states with nonvanishing triality have masses much larger than 1 GeV. The possibility of such a solution to a strongly coupled field theory is exhibited by a calculation employing the variational principle in tree approximation. This procedure reduces the field-theoretical problem to a set of coupled differential equations for classical fields which are just the free parameters of the variational state. A striking property of the solution is that the quark wave function is confined to a thin shell at the surface of the hadronic bound state. Though the quantum corrections to this procedure remain to be investigated systematically, we explore some of the phenomenological implications of the trial wave functions so obtained. In particular, we exhibit the low-lying meson and baryon multiplets of SU(6); their magnetic moments, charge radii, and radiative decays, and the axial charge of the baryons. States of nonvanishing momenta are constructed and the softness of the hadron shell to deformations in scattering processes is discussed qualitatively along with the implications for deep-inelastic electron scattering and dual resonance models.

Deep Inelastic Structure Functions in an Approximation to the Bag Theory

Abstract: A cavity approximation to the bag theory developed earlier is extended to the treatment of forward virtual Compton scattering. In the Bjorken limit and for small values of ω (ω=|2p·qq2|) it is argued that the operator nature of the bag boundaries might be ignored. Structure functions are calculated in one and three dimensions. Bjorken scaling is obtained. The model provides a realization of light-cone current algebra and possesses a parton interpretation. The structure functions show a quasielastic peak. The spreading of the structure functions about the peak is associated with confinement. As expected, Regge behavior is not obtained for large ω. The "momentum sum rule" is saturated, indicating that the hadron's charged constituents carry all the momentum in this model. νWL is found to scale and is calculable. Application of the model to the calculation of spin-dependent and chiral-symmetry-violating structure functions is proposed. The nature of the intermediate states in this approximation is discussed. Problems associated with the cavity approximation are also discussed.

Colour gluons and scaling in a unified gauge model

Abstract: Deep inelastic weak and electromagnetic processes are considered within the parton framework taking the partons to be integrally charged quarks and coloured gluons. Despite the participation of the spin-one gluons in these processes, scaling is shown to be maintained by treating the problem in a unified gauge model based on the groupSU (3)colour⊗SUL (2)⊗U(1). This is a consequence of the vector-dominance type of couplings between the gluons and the weak or electromagnetic vector bosons which are induced by the spontaneous breakdown of gauge symmetry. As a further consequence it is found that in the asymptotic region far above the gluon masses the colour octet parts of the weak and electromagnetic currents of the quarks are damped so that, in particular, the integrally charged quarks behave as fractionally charged quarks in this region.

Quarks with color and flavor

Abstract: The three kinds of quarks, arbitrarily assigned different flavors and colors, are discussed in relation to the structure of particles. (JFP)

Production of the new resonances in hadronic collisions

Abstract: The variation with energy and with Feynman’s variablex of the production of ψ and ψ’ is a sensitive test of their production mechanism. A simple parton model predicts that at relatively low energies production nearx=0 is strongly favoured and that the invariant crosssection atx=0 increases by two orders of magnitude between BNL and ISR energies. A sharp increase is also predicted for the ratio of ψ or ψ’ production to the nonresonant lepton pair background.

Asymptotic freedom and the "absence" of vector-gluon exchange in wide-angle hadronic collisions

Abstract: The naive, pointlike parton model of Berman, Bjorken, and Kogut is generalized to scale-invariant and asymptotically free field theories. The asymptotically free field generalization is studied in detail. Although such theories contain vector fields, single vector-gluon exchange contributes insignificantly to wide-angle hadronic collisions. This follows from (1) the smallness of the invariant charge at small distances and (2) the breakdown of naive scaling in these theories. These effects should explain the apparent absence of vector exchange in inclusive and exclusive hadronic collisions at large momentum transfers observed at Fermilab and at the CERN ISR.

Jet structure and scaling in e + e − annihilation

Abstract: An uncorrelated jet model, with randomly oriented jet axis and parameters as determined from high-energy hadronic interactions, is applied to e+e− annihilation. The resulting features (multiplicities, spectra, correlations, branching ratios) are calculated both at finite c.m.s. energies ((3÷5) GeV) and asymptotically, in order to study the approach to asymptotic behaviour expected for quark, parton and similar models. It is shown that such descriptions, where the jet structure is the same as in hadron-hadron interactions, lead for kinematic reasons to very late scaling of the normalized inclusive hadron distribution. Our results are compared with cluster models for e+e− annihilation and with data.

Neutrinos and nucleon structure

Abstract: ‘Deep inelastic’ collisions of neutrinos and antineutrinos with nucleons behave as if the nucleon Was composed of pointlike constituents (partons and antipartons). Neutrino experiments can measure the net number of (partons-antipartons), their angular momentum and mean square charge; they are 3 in number, have spin 9 and possess the fractional charges postulated ten years ago for the fundamental quarks, by Gell-Mann and Zweig. However, the observation of neutral as well as charged currents in neutrino reactions has compelled introduction of further quantum numbers; for example, a fourth quark with ‘charm’. Recent electron-positron collision experiments also suggest new degrees of freedom—‘charm’ and/or ‘colour’. The effects of these and other modifications to the quark model on neutrino cross-sections are discussed.

Production of baryons with large transverse momentum

Abstract: The multiple scattering of constituent quarks provides a natural mechanism for fairly copious production of large-transverse-momentum baryons in nucleon--nucleon collisions. The predicted scaling law agrees well with available data, and the mechanism provides a qualitative explanation of nuclear- target effects. In comparison with previous parton models, correlations are predicted to be qualitatively different, and large-pT baryon production by meson beams is relatively suppressed. (AIP)

General space-time structure of the neutral-current interactions

Abstract: We present a general analysis of the neutral-current inclusive cross section taking into account all the covariants (scalar, pseudoscalar, tensor, vector, and axial-vector) in the interaction. We derive the model-independent formula for the inclusive cross section and we also discuss the consequences of various models. We deduce bounds on the ratio R equivalent sigma (nu-barN)/sigma ($nu$N) in the case in which scaling is true, i.e., the inclusive cross section at high energies is proportional to the incident neutrino energy E. The scaling violations arising from spin not-equal 1/2 partons and the bounds of R in that case are also discussed.

Quantization Quark Fields on a Lightlike Plane

Abstract: We investigate some problems in quantizing quark fields on a lightlike hyperplane. The generators of the stability group of the quantization plane and the lightlike charges play a central role. The set of these observables is denoted by '=! +· The properties of creation and anniliilation operators of quarks are investigated in detail. It is shown that one-partiCle states' can be determined by the measurement of some observables belonging to '=! +· Also discus~ed is the problem of the independent preparation of two-partiCle states on a lightlike plane. § l. Introduction The original idea of formulating field theories on a hyperplane tangent to the light-cone goes back to Dirac.n In hadron physics the technique of taking the infinite momentum limie> appeared as a precursor of the· formulation in which fields are quantized on such a hyperplane (abbreviated hereafter as the lightlike plane). Soon the kinematical properties of the Poincare generators in this new approach became clear, 3> and the utility of choosing such generators in hadron physics was stressed. The importance of the notions of lightlike charges and an algebra they generate was also fully recognized.•> Feynman rules in this formula­ tion of quantum electrodynamics were obtained, 5> and mathematically rigorous treat­ ments have been investigated. 6> The lightlike quantization is convenient for studying the structure functions in the scaling region of electrol).-proton inclusive experiments.n The parton model proposed by Feynman 8> is easier to investigate in this formulation than in the original infinite momentum frame. It seems very likely that partons are to be identified with ,the quarks quantized on a lightlike plane. 9> The motivation of the present author to this quantization came from the possible utility of lightlike chiral algebra for hadron resonances.10l· One· aim of this work is to present the ligh tlike formulation in a way suitable for applications to the problem of hadron resonances and to prepare the same language for the quark model and the parton model. The formulation of field theory is characterized by the structure of the stability group of a plane on which fields are quantized. By the stability group of a plane we mean the subgroup of the Poincare group which keeps the plane invariant. (It may be modified by a cer.t~in unitary transformation.) In the lightlike for