122 Matching Results

Search Results

Advanced search parameters have been applied.

Off-forward parton distribution

Description: Recent developments in studying off-forward parton distributions are discussed. In this talk, the author discusses the recent developments in studying the off-forward parton distributions (OFPD`s). He has written a topical review article on the subject, which will soon be published in Journal of Physics G. The interested audience can consult that article for details. His talk consists of three parts: definition of the new distributions, their physical significance, and experimental measurements.
Date: December 1, 1998
Creator: Ji, X.
Partner: UNT Libraries Government Documents Department

Antiquark distributions in the proton

Description: This is the final report of a three-year Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The study of quark and antiquark distributions in the nucleon has been a major endeavor in nuclear and particle physics. Results from a recent deep-inelastic scattering experiment suggest the surprising possibility that the up and down antiquark distributions in the proton are not symmetric. A sensitive and direct determination of the antiquark distributions in the proton can be made by comparing the Drell-Yan cross sections on hydrogen versus deuterium targets. The authors have proposed a new experiment (E866) at Fermilab to carry out such measurements. E866 has been taking data since September 1996. Preliminary results show that the apparatus is working very well. The authors anticipate having seven months of beam in 1997, which would allow them to achieve the sensitivities for a definitive measurement of flavor symmetry of sea quarks in the proton.
Date: July 1, 1997
Creator: Brooks, M.; Carey, T. & Garvey, G.
Partner: UNT Libraries Government Documents Department

Measurement of double parton scattering at CDF

Description: A strong signal for Double Parton scattering (DP) is observed in {anti p}p {yields} {gamma} + 3 jets data from the CDF experiment. The process-independent DP parameter, {sigma}{sub eff}, is obtained using a new technique. The result, {sigma}{sub eff} =(14.5{+-}1.7{sup + 1.7}{sub -2.3}) mb, represents a significant improvement over previous measurements. For the first time, the Feynman x dependence of the {sigma}{sub eff} parameter is investigated, and no dependence is seen.
Date: June 1, 1997
Creator: Behrends, S. B. & Lamoureux, J.
Partner: UNT Libraries Government Documents Department

Electroproduction of light quark baryons

Description: The status of electromagnetic excitation of light quark (u, d) baryon states is reviewed and confronted with results of calculations within the framework of microscopic models of the baryon structure and the photon - baryon coupling. Prospects for a qualitative improvement of their knowledge in this sector using photon and electron beams at the new, intermediate energy continuous wave (CW) electron machines are discussed.
Date: April 1, 1992
Creator: Burkert, V.
Partner: UNT Libraries Government Documents Department

Probing the structure of nucleons in electromagnetic interactions

Description: The author discusses open problems in nucleon structure studies using electromagnetic probes. The focus is on the regime of strong interaction QCD. Significant progress in their understanding of the nucleon structure in the region of strong QCD may be expected in the first decade of the new millennium due to major experimental and theoretical efforts currently underway in this field.
Date: June 1, 1999
Creator: Burkert, V.D.
Partner: UNT Libraries Government Documents Department

Baryons and QCD

Description: The author presents an idiosyncratic view of baryons which calls for a marriage between quark-based and hadronic models of QCD. He advocates a treatment based on valence quark plus glue dominance of hadron structure, with the sea of q pairs (in the form of virtual hadron pairs) as important corrections.
Date: March 1, 1997
Creator: Isgur, Nathan
Partner: UNT Libraries Government Documents Department

Probing the structure of nucleons in the resonance region

Description: Status, open questions, and future prospects of the physics of excited nucleons are discussed. Emphasis is on the study of the structure of nucleons via measurements of their electromagnetic transition form factors, the search for ''missing'' resonances, the spin structure of the nucleon in the resonance region, and connections between the resonance and the deep-inelastic regimes.
Date: May 1, 2000
Creator: Burkert, Volker D.
Partner: UNT Libraries Government Documents Department

x-dependent polarized parton distributions

Description: Using QCD motivated and phenomenological considerations, they construct x- dependent polarized parton distributions, which evolve under GLAP evolution, satisfy DIS data and are within positivity constraints. Each flavor is done separately and the overall set can be used to predict polarization asymmetries for various processes. They perform their NLO analysis strictly in x space, avoiding difficulties in moment inversion. Small-x results and other physical considerations are discussed.
Date: March 1, 1998
Creator: Gordon, Lionel E.; Goshtasbpour, Mehrdad & Ramsey, Gordon P.
Partner: UNT Libraries Government Documents Department

Quark and proton spin structure in the Instanton Liquid Model of QCD

Description: Within an instanton based model of QCD the authors address the important question of how much of the proton spin is carried by the spins of the quarks and how much is due to orbital angular momentum and the spins of the gluons. Since this question arises already on the level of a single quark inside the proton, they study axial vector correlation functions for a quark in the so called Random Instanton Liquid Model (RILM) as well as for the Interacting Instanton Liquid Model (IILM).
Date: December 1, 1997
Creator: Blotz, A. & Shuryak, E.
Partner: UNT Libraries Government Documents Department

31305: Tevatron searches for compositeness

Description: Tevatron experiments have recently set or improved limits on quark and lepton compositeness. Included here are results from {radical}s = 1.8 TeV p{anti p} collider experiments D0 and CDF and from fixed target neutrino experiment CCFR, who report limits on quark-quark, quark-lepton, and quark-neutrino compositeness, respectively.
Date: November 1, 1997
Creator: Gallas, E. & Collaborations, E740 and E741
Partner: UNT Libraries Government Documents Department

QCD and hadron structure

Description: I give a brief and selective overview of QCD as it pertains to determining hadron structure, and the relevant directions in this field for nuclear theory. This document is intended to start discussion about priorities, not end it.
Date: June 1, 1995
Creator: Kaplan, D.B.
Partner: UNT Libraries Government Documents Department

Polarized structure functions of the nucleon in the resonance region

Description: Aspects of the spin structure functions of proton and neutrons at low momentum transfer Q{sup 2} and energy transfer, {nu}, i.e. in the region of the nucleon resonances are discussed. Experiments to measure A{sub 1}{sup p}, A{sub 2}{sup p} and A{sub 1}{sup n} structure functions at CEBAF in a Q{sup 2} range from 0.15 to 2.0 GeV{sup 2}, and a W range from threshold to 2.2 GeV are presented.
Date: January 1, 1994
Creator: Burkert, Volker
Partner: UNT Libraries Government Documents Department

Proton structure in proton-antiproton collisions

Description: Proton-antiproton collisions at the Fermilab Tevatron collider currently offer the highest energy collisions available in the laboratory. In this paper the authors briefly discuss measurements which are sensitive to the internal structure of the proton. They also describe measurements which search for substructure in the partons, the quarks and gluons which form the proton.
Date: July 18, 2000
Creator: Montgomery, H. E.
Partner: UNT Libraries Government Documents Department

A comparison of spin observable predictions for RHIC

Description: There have been many versions of spin-dependent parton distributions in the literature. Although most agree with present data within uncertainties, they are based upon different physical assumptions. Some physical models are discussed and the corresponding predictions for double spin asymmetries are shown. A summary of the most feasible measurements in the appropriate kinematic regions at RHIC, which should yield the most useful information about the polarized gluon distribution, is given.
Date: February 2, 2000
Creator: Ramsey, G. P.
Partner: UNT Libraries Government Documents Department

QCD and the structure of the nucleon in electron scattering

Description: The internal structure of the nucleon is discussed within the context of QCD. Recent progress in understanding the distribution of flavor and spin in the nucleon is reviewed, and prospects for extending the author's knowledge of nucleon structure in electron scattering experiments at modern facilities such as Jefferson Lab are outlined.
Date: June 1, 2000
Creator: Melnitchouk, W.
Partner: UNT Libraries Government Documents Department

Anisotropic Magnetism in Field-Structured Composites

Description: Magnetic field-structured-composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g. rotating) magnetic fields, while polymerizing the suspending resin. A uniaxial field produces chain-like particle structures, and a biaxial field produces sheet-like particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCS of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material.
Date: June 24, 1999
Creator: Anderson, Robert A.; Martin, James E.; Odinek, Judy & Venturini, Eugene
Partner: UNT Libraries Government Documents Department

The theory of hadronic systems. Annual progress report

Description: This report briefly discusses progress on the following topics: isospin breaking in the pion-nucleon system; direct capture of pions into deeply bound atomic states; knock out of secondary components in the nucleus; study of the radii of neutron distributions in nuclei; the hadronic double scattering operator; transparency in pion production; asymmetry in pion scattering and charge exchange from polarized nuclei; the mechanism of pion absorption in nuclei; the neutron-proton charge-exchange reaction; modification of the fundamental structure of nucleons in nuclei; and antiproton annihilation in nuclei.
Date: April 12, 1993
Creator: Gibbs, W.R.
Partner: UNT Libraries Government Documents Department

The theory of hadronic systems

Description: This report briefly discusses progress on the following topics: isospin breaking in the pion-nucleon system; subthreshold amplitudes in the {pi}N system; neutron-proton charge-exchange; transparency in pion production; energy dependence of pion DCX; direct capture of pions into deeply bound atomic states; knock out of secondary components in the nucleus; radii of neutron distributions in nuclei; the hadronic double scattering operator; pion scattering and charge exchange from polarized nuclei; pion absorption in nuclei; modification of nucleon structure in nuclei; and antiproton annihilation in nuclei.
Date: March 16, 1995
Creator: Gibbs, W.R.
Partner: UNT Libraries Government Documents Department

Using spin to probe hadronic structure

Description: The theoretical and experimental status of high energy spin phenomena is summarized, with emphasis on the spin properties of nucleons. It is stressed that crucial tests of the Standard Model can be made with polarization experiments. By performing the experiments discussed here, the authors will reveal important constituent and composite properties of protons and neutrons. The future prospects for planned polarization experiments are discussed.
Date: December 2, 1994
Creator: Ramsey, G.P.
Partner: UNT Libraries Government Documents Department

The E2/M1 ratio in {Delta} photoproduction

Description: New high-precision measurements of p({rvec {gamma}}, {pi}) and p({rvec {gamma}}, {gamma}) cross sections and beam asymmetries have been combined with other polarization ratios in a simultaneous analysis of both reactions. The E2/M1 mixing ratio for the n {r_arrow} {Delta} transition extracted from this analysis is EMR = {minus}3.0% {+-} 0.3 (stat+sys) {+-} 0.2 (model).
Date: October 1, 1997
Creator: Hoblit, S.; Blanpied, G.; Blecher, M. & Collaboration, LEGS
Partner: UNT Libraries Government Documents Department

The quark and meson structure in the instanton liquid model

Description: Within an instanton based model of QCD the authors address the important question of how much of the proton spin is carried by the spins of the quarks and how much is due to orbital angular momentum and the spins of the gluons. Since this question arises already on the level of a single quark inside the proton, they study the axial vector correlation function as well as the anomaly correlator for quarks in the so called Random Instanton Liquid Model (RILM) as well as for the Interacting Instanton Liquid Model (IILM).
Date: December 31, 1997
Creator: Blotz, A. & Shuryak, E.
Partner: UNT Libraries Government Documents Department

Strange vector currents and the OZI-rule

Description: The authors investigate the role of correlated {pi}{rho} exchange in the extraction of matrix elements of the strange vector current in the proton. They show that a realistic isoscalar spectral function including this effect leads to sizably reduced strange vector form factors based on the dispersion--theoretical analysis of the nucleons' electromagnetic form factors.
Date: January 1, 1997
Creator: Meisner, U.; Mull, V.; Speth, J. & Orden, J. Van
Partner: UNT Libraries Government Documents Department