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Quark confinement in a constituent quark model

Description: On the level of an effective quark theory, we define confinement by the absence of quark anti-quark thresholds in correlation function. We then propose a confining Nambu-Jona-Lasinio-type model. The confinement is implemented in analogy to Anderson localization in condensed matter systems. We study the model`s phase structure as well as its behavior under extreme conditions, i.e. high temperature and/or high density.
Date: July 1, 1995
Creator: Langfeld, K. & Rho, M.
Partner: UNT Libraries Government Documents Department

Spin of the proton

Description: The author argues that their response to the spin crisis should not be to abandon the naive quark model baby, but rather to allow it to mature. In particular, he advocates dressing the baby in qq pairs, first showing that this can be done without compromising the naive quark model's success with either spectroscopy or the OZI rule. Finally, he shows that despite their near invisibility elsewhere, pairs do play an important role in the proton's spin structure by creating an antipolarized qq sea. In the context of an explicit calculation he demonstrates that it is plausible that the entire ''spin crisis'' arises from this effect.
Date: December 1, 1996
Creator: Isgur, Nathan
Partner: UNT Libraries Government Documents Department

Physics of low-lying hadrons in quark model and effective hadronic approaches. Final report, September 1, 1996 - March 31, 2000

Description: There were basically three theoretical projects supported by this grant: (1) Use of confined quark models to study low energy hadronic processes; (2) Production of strangeness by Electromagnetic Probes; and (3) Diffractive dissociative production of vector mesons by virtual photons on nucleons. Each of them is summarized in the paper.
Date: June 19, 2000
Creator: Mizutani, T.
Partner: UNT Libraries Government Documents Department

Quasi two-body decays of nonstrange baryons.

Description: We examine the decays of nonstrange baryons to the final states Delta Pi, NRho, NEta, NEta', Nw, N.5 (1440)Pi, and Delta 3/2+(1600)Pi, in a relativized pair-creation (^3Po) model which has been developed in a previous study of the NPi decays of the same baryon states.As it is our goal to provide a guide for the possible discovery of new baryon states at CEBAF and elsewhere, we examine the decays of resonances which have already been seen in the partial-wave analyses, along with those of states which are predicted by the quark model but which remain undiscovered.The level of agreement between our calculation and the available widths from the partial-wave analyses in encouraging.
Date: August 1, 1993
Creator: Roberts, Winston & Capstick, Simon
Partner: UNT Libraries Government Documents Department

Radial and orbital q{anti q} excitations: ``Higher quarkonia``

Description: Identification of the spectrum of non-{ital q{anti q}} exotica such as glueballs, hybrids and molecules will require a detailed understanding of radially and orbitally excited quarkonia, since these states are a background to non-{ital q{anti q}} states. The data likely to become available experimentally on these higher-mass resonances are their total widths and strong branching fractions to dominant modes. We advocate the use of these branching fractions to distinguish quarkonia from exotica; in this contribution we summarize our recent detailed {sup 3}P{sub 0} decay model calculations of the 374 two-body open-flavor decay modes of the 32 lightest {ital n{anti n}} states above 1S and 1P, which should be useful for this program.
Date: December 31, 1996
Creator: Barnes, T.
Partner: UNT Libraries Government Documents Department

Parton distributions from SMC and SLAC data

Description: We have extracted spin-weighted parton distributions in a proton from recent data at CERN and SLAC. The valence, sea quark and Antiquark spin-weighted distributions are determined separately. The data are all consistent with a small to moderate polarized gluon distribution, so that the anomaly term is not significant in the determination of the constituent contributions to the spin of the proton. We have analyzed the consistency of the results obtained from various sets of data and the Biorken sum rule. Although all data are consistent with the sum rule, the polarized distributions from different experiments vary, even with higher order QCD corrections taken into account. Results split into two models, one set implying a large polarized strange sea which violates the positivity bound, and the other set yielding a smaller polarized strange sea. Only further experiments which extract information about the polarized sea will reconcile these differences. We suggest specific experiments which can be performed to determine the size of the polarized sea and gluons.
Date: January 4, 1996
Creator: Ramsey, G. P. & Goshtasbpour, M.
Partner: UNT Libraries Government Documents Department

Light-cone quantization and QCD phenomenology

Description: In principle, quantum chromodynamics provides a fundamental description of hadronic and nuclear structure and dynamics in terms of their elementary quark and gluon degrees of freedom. In practice, the direct application of QCD to reactions involving the structure of hadrons is extremely complex because of the interplay of nonperturbative effects such as color confinement and multi-quark coherence. A crucial tool in analyzing such phenomena is the use of relativistic light-cone quantum mechanics and Fock state methods to provide tractable and consistent treatments of relativistic many-body systems. In this article we present an overview of this formalism applied to QCD, focusing in particular on applications to the final states in deep inelastic lepton scattering that will be relevant for the proposed European Laboratory for Electrons (ELFE), HERMES, HERA, SLAC, and CEBAF. We begin with a brief introduction to light-cone field theory, stressing how it many allow the derivation of a constituent picture, analogous to the constituent quark model, from QCD. We then discuss several applications of the light-cone Fock state formalism to QCD phenomenology. The Fock state representation includes all quantum fluctuations of the hadron wavefunction, including far off-shell configurations such as intrinsic charm and, in the case of nuclei, hidden color. In some applications, such as exclusive processes at large momentum transfer, one can make first-principle predictions using factorization theorems which separate the hard perturbative dynamics from the nonpertubative physics associated with hadron binding. The Fock state components of the hadron with small transverse size, which dominate hard exclusive reactions, have small color dipole moments and thus diminished hadronic interactions. Thus QCD predicts minimal absorptive corrections, i.e., color transparency for quasi-elastic exclusive reactions in nuclear targets at large momentum transfer.
Date: December 1995
Creator: Brodsky, S. J. & Robertson, D. G.
Partner: UNT Libraries Government Documents Department

Strangeness in the Nucleon or the quark model beyond the valence approximation

Description: Simple arguments based on unitarity indicate that meson loops diagrams, induced by an underlying qq pair creation process, should badly disturb the phenomenologically successful spectroscopy and dynamics of the valence quark model, including such simple but mysterious regularities as the OZI rule. The author discusses some recent progress in adding pair creation to the valence quark model in a way which provides rationale for the quark model's success.
Date: January 1, 1999
Creator: Isgur, Nathan
Partner: UNT Libraries Government Documents Department

Leptonic production of baryon resonances

Description: In these lectures, the author focuses on the electromagnetic transition between non-strange baryon states. This sector received much attention in the early 1970's after the development of the first dynamical quark models. However, experimental progress was slow, partly because of the low rates associated with electromagnetic interactions, and partly because of the lack of guidance by theoretical models that went beyond the simplest quark models. It was also difficult for experiments to achieve the precision needed for a detailed analysis of the entire resonance region in terms of the fundamental photocoupling amplitudes over a large range in momentum transfer.
Date: March 1, 1994
Creator: Burkert, V.
Partner: UNT Libraries Government Documents Department

Where's the glue: A strong interaction puzzle

Description: After recalling why most strong interaction phenomena cannot be studied with quark-gluon perturbation theory, the author suggests that a phenomenological form of the old dual string theory may be a good model for the nonperturbative aspects of QCD. He begins by describing some recent progress within this framework in understanding the status of the quark model within QCD. The resulting picture of the ordinary hadrons, hybrids, and glueballs provides a simple framework for studying these elements of hadron spectroscopy.
Date: December 1, 1996
Creator: Isgur, Nathan
Partner: UNT Libraries Government Documents Department

Heavy mesons in a relativistic model

Description: Motivated by the present interest in the heavy quark effective theory, the authors use the spectator equations to treat the mesonic bound states of heavy quarks. The kernel they use is based on scalar confining and vector Coulomb potentials. Wave functions are treated to leading order and energies to order 1/m{sub Q} in the heavy-light systems, and order 1/m{sub Q{sup 2}} in heavy-heavy systems. Their results are in reasonable agreement with experimental measurements. They estimate two of the parameters of the heavy quark effective theory, and propose further calculations that may be undertaken in the future.
Date: December 1, 1994
Creator: Zeng, J.; Orden, J. & Roberts, W.
Partner: UNT Libraries Government Documents Department

Valence quark spin distribution functions

Description: The hyperfine interactions of the constituent quark model provide a natural explanation for many nucleon properties, including the {Delta} - N splitting, the charge radius of the neutron, and the observation that the proton's quark distribution function ratio d(x)/u(x) {r_arrow} 0 as x {r_arrow} 1. The hyperfine-perturbed quark model also makes predictions for the nucleon spin-dependent distribution functions. Precision measurements of the resulting asymmetries A{sub 1}{sup p}(x) and A{sub 1}{sup n}(x) in the valence region can test this model and thereby the hypothesis that the valence quark spin distributions are ''normal''.
Date: September 1, 1998
Creator: Isgur, Nathan
Partner: UNT Libraries Government Documents Department

How to extract the P{sub 33}(1232) resonance contributions from the amplitudes M{sub 1{sup +}}{sup 3/2},E{sub 1{sup +}}{sup 3/2},S{sub 1{sup +}}{sup 3/2} of pion electroproduction on nucleons

Description: Within the dispersion relation approach, solutions of integral equations for the multipoles M{sub 1{sup +}}{sup 3/2},E{sub 1{sup +}}{sup 3/2},S{sub 1{sup +}}{sup 3/2} are found at 0 < Q{sup 2} < 3 GeV{sup 2}. These solutions should be used as input for the resonance and nonresonance contributions in the analyses of pion electroproduction data in the P{sub 33}(1232) resonance region. It is shown that the traditional identification of the amplitude M{sub 1{sup +}}{sup 3/2} (as well of the amplitudes E{sub 1{sup +}}{sup 3/2},S{sub 1{sup +}}{sup 3/2}) with the P{sub 33}(1232) resonance contribution is not right; there is a contribution in these amplitudes which has a nonresonance nature and is produced by rescattering effects in the diagrams corresponding to the nucleon and pion poles. This contribution is reproduced by the dispersion relations. Taking into account nonresonance contributions in the amplitudes M{sub 1{sup +}}{sup 3/2},E{sub 1{sup +}}{sup 3/2}, the helicity amplitudes A{sub p}{sup 1/2}, A{sub p}{sup 3/2} and the ratio E2/M1 for the {gamma}N {r_arrow} P{sub 33}(1232) transition are extracted from experiment at Q{sup 2}=0. They are in good agreement with quark model predictions.
Date: August 1997
Creator: Aznauryan, I. G.
Partner: UNT Libraries Government Documents Department

Semileptonic meson decays in the quark model: An update

Description: The authors present the predictions of ISGW2, an update of the ISGW quark model for semileptonic meson decays. The updated model incorporates a number of features which should make it more reliable, including the constraints imposed by Heavy Quark Symmetry, hyperfine distortions of wave-functions, and form factors with more realistic high recoil behaviors.
Date: March 1, 1995
Creator: Scora, D. & Isgur, N.
Partner: UNT Libraries Government Documents Department

Strong decays of heavy hadrons In HQET

Description: The authors discuss the application of the tensor formalism of HQET to the strong decays of heavy hadrons. They treat both meson and baryon decays, and note that all of their results are in agreement with the `spin-counting' arguments of Isgur and Wise. They briefly discuss the possible extension of the formalism to include 1/m corrections.
Date: August 1, 1997
Creator: Roberts, W.
Partner: UNT Libraries Government Documents Department

Beyond the adiabatic approximation: The impact of thresholds on the hadronic spectrum

Description: In the adiabatic approximation, most of the effects of quark-antiquark loops on spectroscopy can be absorbed into a static interquark potential. The author develops a formalism which can be used to treat the residual nonadiabatic effects associated with the presence of nearby hadronic thresholds for heavy quarks. He then defines a potential which includes additional high energy corrections to the adiabatic limit which would be present for finite quark masses. This improved potential allows a systematic low energy expansion of the impact of thresholds on hadronic spectra.
Date: January 1, 1999
Creator: Isgur, N.
Partner: UNT Libraries Government Documents Department

Spin structure of the proton

Description: In these lectures the author argues that their response to the spin crisis should not be to abandon the naive quark model baby, but rather to allow it to mature. He begin by recalling what a beautiful baby the quark model is via an overview of its successes in spectroscopy, dynamics, and valence spin structure. He also introduces the conservative hypothesis that dynamical q{anti q} pairs are its key missing ingredient. He then discusses dressing the baby. He first shows that it can be clothed in glue without changing its spectroscopic successes. In the process, several dynamical mysteries associated with quark model spectroscopy are potentially explained. Next, he dresses the baby in q{anti q} pairs, first showing that this can be done without compromising the naive quark model's success with either spectroscopy or the OZI rule. Finally, he shows that despite their near invisibility elsewhere, pairs do play an important role in the proton's spin structure by creating an antipolarized q{anti q} sea. In the context of an explicit calculation he demonstrate that it is plausible that the entire ''spin crisis'' arises from this effect.
Date: August 1, 1995
Creator: Isgur, Nathan
Partner: UNT Libraries Government Documents Department

The stability of the spectator, Dirac, and Salpeter equations for mesons

Description: Mesons are made of quark-antiquark pairs held together by the strong force. The one channel spectator, Dirac, and Salpeter equations can each be used to model this pairing. The authors look at cases where the relativistic kernel of these equations corresponds to a time-like vector exchange, a scalar exchange, or a linear combination of the two. Since the model used in this paper describes mesons which cannot decay physically, the equations must describe stable states. They find that this requirement is not always satisfied, and give a complete discussion of the conditions under which the various equations give unphysical, unstable solutions.
Date: August 1, 1998
Creator: Uzzo, Michael & Gross, Franz
Partner: UNT Libraries Government Documents Department

Meson decays in a quark model

Description: A recent model of hadron states is extended to include meson decays. The authors find that the overall success of the model is quite good. Possible improvements to the model are suggested.
Date: August 1, 1997
Creator: Roberts, W. & Silvestre-Brac, B.
Partner: UNT Libraries Government Documents Department

Quark Models of Baryon Masses and Decays

Description: The application of quark models to the spectra and strong and electromagnetic couplings of baryons is reviewed. This review focuses on calculations which attempt a global description of the masses and decay properties of baryons, although recent developments in applying large N-c QCD and lattice QCD to the baryon spectrum are described. After outlining the conventional one-gluon-exchange picture, models which consider extensions to this approach are contrasted with dynamical quark models based on Goldstone-boson exchange and an algebraic collective-excitation approach. The spectra and electromagnetic and strong couplings that result from these models are compared with the quantities extracted from the data and each other, and the impact of various model assumptions on these properties is emphasized. Prospects for the resolution of the important issues raised by these comparisons are discussed.
Date: August 2000
Creator: Capstick, Simon & Roberts, W.
Partner: UNT Libraries Government Documents Department

Phenomenological study of strong decays of heavy hadrons in heavy quark effective theory

Description: The application of the tensor formalism of the heavy quark effective theory (HQET) at leading order to strong decays of heavy hadrons is presented. Comparisons between experimental and theoretical predictions of ratios of decay rated for B mesons, D mesons and kaons are given. The application of HQET to strange mesons presents some encouraging results. The spin-flavor symmetry is used to predict some decay rates that have not yet been measured.
Date: December 1999
Creator: Tregoures, N. & Roberts, W.
Partner: UNT Libraries Government Documents Department

Polarized lepton-nucleon scattering

Description: Deep inelastic polarized lepton-nucleon scattering is reviewed in three lectures. The first lecture covers the polarized deep inelastic scattering formalism and foundational theoretical work. The second lecture describes the nucleon spin structure function experiments that have been performed up through 1993. The third lecture discusses implication of the results and future experiments aimed at high-precision measurements of the nucleon spin structure functions.
Date: February 1, 1994
Creator: Hughes, E.
Partner: UNT Libraries Government Documents Department

Hyperons at Fermilab

Description: Magnetic moment measurement of the baryon octet and decouplet have recently been measurements illustrated the success as well as the limitations of the simpple qazrk model. Measurements of hyperon production polarizations have shown this to be a rich and complex process. It has forced us to reconsider our basic understanding of hyperon polarization processes.
Date: November 1, 1995
Creator: Lach, J.
Partner: UNT Libraries Government Documents Department

Discovery mass reach for excited quarks at hadron colliders

Description: If quarks are composite particles then excited states are expected. We estimate the discovery mass reach as a function of integrated luminosity for excited quarks decaying to dijets at the Tevatron the mass reach is 0.94 TeV for Run 11 (2 fb{sup -1}) and 1. 1 TeV for TeV33 (30 fb{sup -1}). At the LHC the mass reach is 6.3 TeV for 100 fb{sup -1}. At a VLHC with a center of mass energy {radical}s, of 50 TeV (200 TeV) the mass reach is 25 TeV (78 TeV) for an integrated luminosity of 10{sup 4} fb{sup -1}. However, an excited quark with a mass of 25 TeV would be discovered at a hadron collider with {radical}s = 100 TeV and an integrated luminosity of 13 fb{sup -1}, illustrating a physics example where a factor of 2 in machine energy is worth a factor of 1000 in luminosity.
Date: September 10, 1996
Creator: Harris, R.M.
Partner: UNT Libraries Government Documents Department