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Hadrons in the Nuclear Medium

Description: Quantum Chromodynamics, the microscopic theory of strong interactions, has not yet been applied to the calculation of nuclear wave functions. However, it certainly provokes a number of specific questions and suggests the existence of novel phenomena in nuclear physics which are not part of the traditional framework of the meson-nucleon description of nuclei. Many of these phenomena are related to high nuclear densities and the role of color in nucleonic interactions. Quantum fluctuations in the spatial separation between nucleons may lead to local high density configurations of cold nuclear matter in nuclei, up to four times larger than typical nuclear densities. We argue here that experiments utilizing the higher energies available upon completion of the Jefferson Laboratory energy upgrade will be able to probe the quark-gluon structure of such high density configurations and therefore elucidate the fundamental nature of nuclear matter. We review three key experimental programs: quasi-elastic electro-disintegration of light nuclei, deep inelastic scattering from nuclei at x>1, and the measurement of tagged structure functions. These interrelated programs are all aimed at the exploration of the quark structure of high density nuclear configurations. The study of the QCD dynamics of elementary hard processes is another important research direction and nuclei provide a unique avenue to explore these dynamics. We argue that the use of nuclear targets and large values of momentum transfer at would allow us to determine whether the physics of the nucleon form factors is dominated by spatially small configurations of three quarks.
Date: October 1, 2002
Creator: Sargsian, Misak; Miller, G.A.; Arrington, John; Bertozzi, William; Boeglin, Werner; Carlson, Carl et al.
Partner: UNT Libraries Government Documents Department

Nucleon spin structure functions from HERMES: The first year

Description: HERMES, {und HE}RA {und Me}asurement of {und S}pin, is a second generation exper to study the spin structure of the nucleon by using polarized internal gas targets in the HERA 28 GeV electron storage ring. Scattered positrons and coincident hadrons are detected in an open geometry spectrometer which includes particle identification. Inclusive data with polarized {sup 3}He give the spin structure function {ital g{sup n}{sub 1}(x)} and the Ellis-Jaffe integral RR{Lambda} = {integral}{sub 0}{sup 1} {ital g{sup n}{sub 1}(x)dx} for the neutron. The semi-inclusive spin asymmetries are a unique and sensitive probe of the flavor dependence of quark helicity distributions and properties of the quark sea. Data taken in 1995 with unpolarized hydrogen and deuterium targets provide measurements of the flavor distributions of sea and valence quarks. In a preliminary analysis, {Lambda}{sup {ital n}}{sub 1} = -0.032{+-}0. 013{sub {ital stat.}} {+-} O.017{sub {ital syst.}} is obtained at Q{sup 2} = 3(GeV/c){sup 2} for the Ellis-Jaffe integral.
Date: December 31, 1996
Creator: Jackson, H.E. & Collaboration, HERMES
Partner: UNT Libraries Government Documents Department

Sea and gluon spin structure function measurements at RHIC

Description: The first polarized collider where one collides 250-GeV/c beams of 70% polarized protons at high luminosity is under construction. This will allow a determination of the nucleon spin-dependent structure functions over a large range in x and a collection of sufficient W and Z events to investigate extremely interesting spin-related phenomena.
Date: February 1, 1995
Creator: Yokosawa, A.
Partner: UNT Libraries Government Documents Department

Measurement of the longitudinal deuteron spin-structure function in deep-inelastic scattering

Description: Experiment E143 at SLAC performed deep-inelastic scattering measurements with polarized electrons incident on polarized protons and deuterons. The data for the beam energy of 29 GeV cover the kinematical range of x{sub Bj} > 0.03 and 1 < Q{sup 2} < 12 GeV{sup 2}. From these data, the spin-dependent structure functions g{sub 1} were determined. This dissertation describes the experiment and its analysis and discusses the results. The measured integral of g{sub 1}{sup d} over x from x = 0 to x = 1 is {Gamma}{sub 1}{sup d} = 0.046 {+-} 0.003 (stat){+-}0.004 (syst) at Q{sup 2} = 3 GeV{sup 2} and disagrees by more than three standard deviations with the prediction of the Ellis-Jaffe, sum rule. The data suggest that the quark contribution to the nucleon helicity is 0.35 {+-} 0.05. From the proton data of the same experiment, the integral over the proton spin-structure functional g{sub 1}{sup d} was determined to be {Gamma}{sub 1}{sup p} = 0.127 {+-} 0.003(stat){+-}0.008(syst). By Combining the deuteron data with the proton data, the integral {Gamma}{sub 1}{sup n} was extracted as {minus}0.027 {+-} 0.008 (stat){+-}0.010 (syst). The integral {Gamma}{sub 1}{sup p} {minus} {Gamma}{sub 1}{sup n} is 0.154{+-}0.010(stat) {+-}0.016 (syst) according to the E143 analysis. This result agrees with the important Bjorken sum rule of 0.171 {+-} 0.009 at Q{sup 2} = 3 GeV{sup 2} within less than one standard deviation. Furthermore, results of a separate analysis involving GLAP evolution equations are shown. Data were also collected for beam energies of 16.2 and 9.7 GeV, Results for g{sub 1} at these energies are presented.
Date: September 1, 1996
Creator: Bauer, J.M.
Partner: UNT Libraries Government Documents Department

Polarized and unpolarized double prommpt photon production in next-to-leading order QCD

Description: We calculate O({alpha}{sub s}) corrections to inclusive and isolated double prompt photon production, both for the unpolarized case, and for longitudinal polarization of the incoming hadrons. The calculation is performed using purely analytical techniques for the inclusive case, and a combination of analytical and Monte Carlo techniques to perform the phase space integration in the isolated case. A brief phenomenological study is made of the process pp {r_arrow} {gamma}{gamma}X at CMS energies appropriate for the RHIC heavy ion collider. 21 refs., 8 figs.
Date: March 1, 1996
Creator: Coriano, C. & Gordon, L.E.
Partner: UNT Libraries Government Documents Department

Review of {alpha}{sub s} measurements

Description: Determinations of {alpha}{sub s} are reviewed. Current results are limited to a precision of around 3--20%, largely by theoretical uncertainties. All measurements are consistent with a world average value of 0.118 {+-} 0.005 and there is no evidence of any discrepancy between low-Q{sup 2} and high-Q{sup 2} results. 71 refs., 1 fig., 1 tab.
Date: October 1, 1996
Creator: Burrows, P.N.
Partner: UNT Libraries Government Documents Department

Selected problems in experimental intermediate energy. Progress report, February 1, 1994--January 31, 1997

Description: A complete description of the research program of the intermediate energy group at the University of Houston may be found in previous progress reports, renewal proposals, and proposals to the various accelerator advisory committees. Recent documents are appended to this report and summaries of current research activities are presented in the next section. The objectives of the research program are to: (1) investigate selected, forefront problems in experimental intermediate energy physics; (2) educate students in this field of research; and, (3) develop the instrumentation necessary to undertake this experimental program. Generally, the research is designed to search for physical processes which cannot be explained by conventional models of elementary interactions. As one example, we use nuclear targets where the nucleus provides a many body environment of strongly interacting particles, and where one attempts to observe the perturbation of a known interaction by this environment. These effects, however, may be masked by the complexity of the many body problem and may be difficult to observe. Therefore, experiments of this type must be carefully chosen and analyzed for deviations from the more conventional models.
Date: September 1, 1995
Creator: Mayes, B.W.; Hungerford, E.V. & Pinsky, L.S.
Partner: UNT Libraries Government Documents Department

Experimental studies of the quark-gluon structure of nucleons and nuclei and of pion- and proton-nucleus interactions. Progress report, April 1, 1994--March 31, 1997

Description: This report summarizes the work on experimental research in intermediate energy nuclear physics carried out by New Mexico State University from April 1, 1994, through March 31, 1996 under a grant from the US Department of Energy. During this period we began phasing out our programs of study of pion-nucleus and pion-nucleon interaction and of nucleon-nucleus charge-exchange reactions, which have been our major focus of the past two or three years. At the same time we continued moving in a new direction of research on studies of the internal structure of nucleons and nuclei in terms of quarks and gluons. The pion and nucleon work has been aimed at improving our understanding of the nature of pion and proton interactions in the nuclear medium and of various aspects of nuclear structure. The studies of the quark-gluon structure of nucleons are aimed at clarifying such problems as the nature of the quark sea and the relation of the nucleon spin to the spins of the quarks within the nucleon, questions which are of a very fundamental nature.
Date: October 1, 1996
Partner: UNT Libraries Government Documents Department

Spin physics at RHIC a new twist on the heavy ion experiments

Description: Operation of RHIC with two beams of highly polarized protons (70%, either longitudinal or transverse) at high luminosity ???? = 2 {circ} 10{sup 32} cm{sup -2} sec{sup -1} for two months/year will allow high statistics studies of polarization phenomena in the perturbative region of hard scattering where both QCD and ElectroWeak theory make detailed predictions for polarization effects. The collision c.m energy, {radical}s = 200 - 500 GeV, represents a new domain for the study of spin. Direct photon production win be used to measure the gluon polarization in the polarized proton. A new twist comes from W-boson production which is expected to be 100% parity violating and will thus allow measurements of flavor separated quark and antiquark (u, u, d, d) polarization distributions. Searches for parity violation in strong interaction processes such as jet and leading particle production will be a sensitive way to look for new physics beyond the standard model, one possibility being quark substructure.
Date: July 3, 1996
Creator: Tannenbaum, M.J.
Partner: UNT Libraries Government Documents Department

The instanton liquid model of QCD

Description: Within a microscopic model for the non-perturbative vacuum of QCD, hadronic correlation functions are calculated. In the model the vacuum is a statistical, interacting ensemble of instantons and anti-instantons at the scale of {Lambda}{sub QCD}. Hadronic two-point as well as three-point correlation functions are evaluated and compared with phenomenological information about the spectra, couplings and form factors. Especially the electro magnetic form factor of the pion is obtained and new predictions for the charm contribution to DIS structure functions are made.
Date: December 1998
Creator: Blotz, A.
Partner: UNT Libraries Government Documents Department

Spin physics at RHIC

Description: Operation of RHIC with two beams of highly polarized protons (70%, either longitudinal or transverse) at high luminosity L = 2 x 10{sup 32} cm{sup -2} sec{sup -1} for two months/year will allow the STAR and PHENIX detectors to perform high statististics studies of polarization phenomena in the perturbative region of hard scattering where both QCD and ElectroWeak theory make detailed predictions for polarization effects. The collision c.m. energy, {radical}s = 200 - 500 GeV, represents a new domain for the study of spin. Direct photon production will be used to measure the gluon polarization in the polarized proton. A new twist comes from W-boson production which is expected to be 100% parity violating and will thus allow measurements of flavor separated Quark and antiquark (u, {bar u}, d, {bar d}) polarization distributions. Searches for parity violation in strong interaction processes such as jet and leading particle production will be a sensitive way to look for new physics beyond the standard model, one possibility being quark substructure.
Date: September 6, 1996
Creator: Tannenbaum, M.J.
Partner: UNT Libraries Government Documents Department

A theoretical overview on single hard diffraction

Description: The concept of the Pomeron structure function and its application in Single Hard Diffraction at hadron colliders and in diffractive Deep Inelastic Scattering is critically reviewed. Some alternative approaches are briefly surveyed with a focus on QCD inspired models.
Date: December 31, 1996
Creator: Wuesthoff, M.
Partner: UNT Libraries Government Documents Department

Selected problems in experimental intermediate energy physics. Final technical report, February 1, 1991--January 31, 1994

Description: A complete description of the research program of the intermediate energy group at the University of Houston may be found in previous progress reports, renewal proposals, and proposals to various accelerator advisory committees. The summaries of activities are presented in the next section. The objectives of the research program are to: (1) investigate selected, forefront problems in experimental intermediate energy physics; (2) educate students in this field of research; and (3) develop the instrumentation necessary to undertake this experimental program. There were three major thrusts of the program: (1) strange particle physics, where a strange quark is embedded in the nuclear medium; (2) muon electro-weak decay, which involves a search for a violation of the standard model of the electro-weak interaction; and (3) measurement of the spin dependent structure function of the neutron and proton.
Date: October 1, 1997
Creator: Mayes, B.W.; Hungerford, E.V. & Pinsky, L.S.
Partner: UNT Libraries Government Documents Department

From HERA to the Tevatron: A scaling law in hard diffraction

Description: Results on hard diffraction from CDF are reviewed and compared with predictions based on the diffractive structure function of the proton measured in deep inelastic scattering at HERA. The predictions are generally larger than the measured rates by a factor of {approximately} 6, suggesting a breakdown of conventional factorization. Correct predictions are obtained by scaling the rapidity gap probability distribution of the diffractive structure function to the total integrated gap probability. The scaling of the gap probability is traced back to the pomeron flux renormalization hypothesis, which was introduced to unitarize the soft diffraction amplitude.
Date: December 4, 1997
Creator: Goulianos, K. & CDF
Partner: UNT Libraries Government Documents Department

Measurement of the deuteron elastic structure functions up to large momentum transfers

Description: The cross section for elastic electron-deuteron scattering was measured in JLab experiment 91-026. The deuteron elastic structure functions A(Q{sup 2}) and B(Q{sup 2}) have been extracted from this data. The final results for the ``electric'' structure function A(Q{sup 2}), in the range of 0.7 less than or equal to Q{sup 2} less than or equal to 6.0 (GeV/c){sup 2} are presented. Preliminary results for the ``magnetic'' structure function B(Q{sup 2}) are presented in the range of 0.7 less than or equal to Q{sup 2} less than or equal to 1.35 (GeV/c){sup 2}. These data are compared with theoretical predictions of both meson-nucleon and quark-gluon based models.
Date: February 1, 1999
Creator: de Jager, Kees
Partner: UNT Libraries Government Documents Department

Electromagnetic structure of the deuteron

Description: Recent measurements of the deuteron electromagnetic structure functions A, B, and T{sub 20} extracted from high energy elastic ed scattering, and the cross sections and asymmetries extracted from high energy photodisintegration gamma + d to n + p, are reviewed and compared to theory. The theoretical calculations range from nonrelativistic and relativistic models using the traditional meson and baryon degrees of freedom, to effective field theories, to models based on the underlying quark and gluon degrees of freedom of QCD, including nonperturbative quark cluster models and perturbative QCD. We review what has been learned from these experiments, and discuss why elastic ed scattering and photodisintegration seem to require very different theoretical approaches, even though they are closely related experimentally.
Date: November 1, 2001
Creator: Gilman, R. & Gross, Franz
Partner: UNT Libraries Government Documents Department

Quark-hadron duality and the nuclear EMC effect

Description: Recent data on polarized proton knockout reactions off He-4 nuclei suggest a small but nonzero modification of proton electromagnetic form factors in medium. Using model independent relations derived on the basis of quark-hadron duality, we relate the medium modification of the form factors to the modification at large x of the deep-inelastic structure function of a bound proton. This places strong constraints on models of the nuclear EMC effect which assume a large deformation of the intrinsic structure of the nucleon in medium.
Date: November 1, 2001
Creator: Melnitchouk, W.; Tsushima, K. & Thomas, A.W.
Partner: UNT Libraries Government Documents Department

e-A PHYSICS AT A COLLIDER.

Description: An electron-nucleus (e-A) collider with center-of-mass energy in excess of 50 GeV per electron-nucleon collision will allow the physics community to obtain unprecedented new knowledge of the partonic structure of nuclei. If reliable information is to be extracted on these partonic densities, it is essential to realize that with our current level of understanding of QCD, momentum transfers to the struck partons greater than 1 GeV/c are necessary. This requirement puts a priority on high center-of-mass energy if partonic densities are to be measured over a wide range. Comparing the partonic structure of the free nucleon to that of bound nucleons and measuring the systematic changes in that structure as a function of nucleon number (A) will provide deeper insight into the origins and dynamics of nuclear binding. In addition, e-A collisions will allow the exploration of partonic densities appreciably higher than is accessible in e-p collisions. An e-A collider will allow one to measure the gluonic structure functions of nuclei down to x {approx} 10{sup -3}, information valuable in its own right and essential to a quantitative understanding of highly relativistic A-A collisions. The time-space evolution of partons can only be investigated by studying the modifications of hard collisions that take place when nuclear targets are employed. In a hard collision the partonic fragments interact, hadronize, and reinteract on their way to the distant detectors without revealing their evolution into the hadrons finally detected. Nuclear targets of differing A place varying amounts of nuclear matter in proximity to the hard collision producing unique information about the quantum fluctuations of incident projectile prior to the collision and on the early evolution of the produced partons. Using charged leptons (e, {mu}) to investigate this physics has been the richest source of information to date and extending the reach of these investigations ...
Date: January 9, 2001
Creator: GARVEY, G. T.
Partner: UNT Libraries Government Documents Department

Moments of Structure Functions in Full QCD

Description: Moments of the quark density distribution, moments of the quark helicity distribution, and the tensor charge are calculated in full QCD. Calculations of matrix elements of operators from the operator product expansion have been performed on 16{sup 3} x 32 lattices for Wilson fermions at {beta} = 5.6 using configurations from the SESAM collaboration and at {beta} = 5.5 using configurations from SCRI. One-loop perturbative renormalization corrections are included. Selected results are compared with corresponding quenched calculations and with calculations using cooled configurations.
Date: August 1, 2000
Creator: Dolgov, D.; Brower, R.; Capitani, S.; Negele, J. W.; Pochinsky, A.; Renner, D. et al.
Partner: UNT Libraries Government Documents Department

New Results for the Charged Pion Electromagnetic Form Factor

Description: Separated longitudinal and transverse structure functions for the reaction {sup 1} H(e, e'pi{sup +})n were measured in the momentum transfer region Q{sup 2}=0.6-1.6(GeV/c){sup 2} at a value of the invariant mass W=1.95 GeV. New values for the pion charge form factor were extracted from the longitudinal cross section by using a recently developed Regge model. The results indicate that the pion form factor in this region is larger than previously assumed and is consistent with a monopole parameterization fitted to very low Q{sup 2} elastic data.
Date: October 1, 2000
Creator: Volmer, J.
Partner: UNT Libraries Government Documents Department

Pole term and gauge invariance in deep inelastic scattering

Description: In this paper the authors reconcile two contradictory statements about deep inelastic scattering (DIS) in manifestly covariant theories: (1) the scattering must be gauge invariant, even in the deep inelastic limit, and (2) the pole term (which is not gauge invariant in a covariant theory) dominates the scattering amplitude in the deep inelastic limit. An ``intermediate'' answer is found to be true. They show that, at all energies, the gauge dependent part of the pole term cancels the gauge dependent part of the rescattering term, so that both the pole and rescattering terms can be separately redefined in a gauge invariant fashion. The resulting, redefined pole term is then shown to dominate the scattering in the deep inelastic limit. Details are worked out for a simple example in 1+1 dimensions.
Date: March 1, 1998
Creator: Batiz, Zoltan & Gross, Franz
Partner: UNT Libraries Government Documents Department

A Covariant Description of the Deuteron

Description: An introduction to the use of Bethe-Salpeter and quasipotential equations in the description of electron scattering from the deuteron is provided. The basic formalism and many technical issues are introduced in the context of a simple scalar theory. Results for bound-state wave functions and scattering phases shifts for a variety of quasipotential prescriptions are presented and qualitative characteristics of these solutions are discussed. The elastic form factors for the bound state in this model are calculated using the spectator or Gross equation. The calculations are then extended to account for the complexities associated with nucleon spin and results are presented for the elastic structure functions of the deuteron using the spectator equation. This calculation is shown to produce a good description of elastic electron scattering from the deuteron over the range of momentum transfers for which data are available.
Date: June 1, 1994
Creator: Orden, J. Van
Partner: UNT Libraries Government Documents Department

A local dynamic correlation function from inelastic neutron scattering

Description: Information about local and dynamic atomic correlations can be obtained from inelastic neutron scattering measurements by Fourier transform of the Q-dependent intensity oscillations at a particular frequency. A local dynamic structure function, S(r,{omega}), is defined from the dynamic scattering function, S(Q,{omega}), such that the elastic and frequency-integrated limits correspond to the average and instantaneous pair-distribution functions, respectively. As an example, S(r,{omega}) is calculated for polycrystalline aluminum in a model where atomic motions are entirely due to harmonic phonons.
Date: July 13, 1997
Creator: McQueeney, R.J.
Partner: UNT Libraries Government Documents Department

Issues in leading particle and charm production in DIS at HERA.

Description: A Monte Carlo simulation based on {Omicron}({alpha}{sub s}) QCD matrix elements matched to parton showers shows that final-state hadrons in DIS can be used to tag events with a single (anti)quark recoiled against the proton. The method is particularly suited to study the mean charge of leading particles, which is sensitive to fragmentation and sea quark contribution to the proton structure function. They also discuss methods to study the charm production in DIS using the Breit frame.
Date: August 31, 1999
Creator: Chekanov, S. V.
Partner: UNT Libraries Government Documents Department