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Probing the strange nature of the nucleon with phi photoproduction

Description: The presence inside the nucleon of a significant component of strange-antistrange quark pairs has been invoked to explain a number of current puzzles in the low energy realm of QCD. The {sigma} term in {pi}N scattering is a venerable conundrum which can be explained with a 10%--20% admixture. The spin crisis brought on by the EMC result and follow on experiments was first interpreted as requiring a large strange content of s quarks whose spin helped cancel the contribution of the u and d quarks to the nucleon spin, again of order 10%. Excess phi meson production in p{anti p} annihilation at LEAR has also been explained in terms of up to a 19% admixture of s{anti s} pairs. Charm production in deep-inelastic neutrino scattering would appear to provide evidence for a 3% strange sea. It is clear that a definite probe of the strange quark content would be an invaluable tool in unraveling a number of mysteries. The longitudinal beam target asymmetry in {psi} photoproduction is a particularly sensitive probe of that content. It is explored here.
Date: March 6, 1997
Creator: Lowry, M.M.
Partner: UNT Libraries Government Documents Department

Comment on ''Parton distributions, d/u, and higher twist effects at high x''

Description: In a recent Letter Yang and Bodek presented results of a new analysis of proton and deuteron structure functions in which the free neutron structure function F{sub 2}{sup n}, was extracted at large x. Knowledge of F{sub 2}{sup n} is crucial for determining the neutron/proton structure function ratio, whose x {r_arrow} 1 limit is sensitive to mechanisms of SU(6) spin-flavor symmetry breaking, and provides one of the fundamental tests of the x dependence of parton distributions in perturbative QCD. Relating nuclear structure functions to those of free nucleons is, however, not straightforward because at large x nuclear effects become quite sizeable. In particular, omitting nuclear binding or off-shell corrections can introduce errors of up to 50% in F{sub 2}{sup n}/F{sub 2}{sup p} already at x {approximately} 0.75. Rather than follow the conventional procedure of subtracting Fermi motion and binding effects in the deuteron via standard two-body wave function, Yang and Bodek instead extract F {sub 2}{sup n} by extrapolating the density dependence of the nuclear corrections to the case of the deuteron. Here the authors point out why this approach is likely to be misleading for light nuclei, and correctly applied predicts that the nuclear correction in the deuteron should be zero.
Date: November 1, 1999
Creator: Melnitchouki, W.; Afnan, I. R.; Bissey, F. & Thomas, A. W.
Partner: UNT Libraries Government Documents Department

New Insights into the EMC Effect

Description: Deep-inelastic scattering cross section ratios plotted as a function of the Bjorken scaling variable, xB, show an unexpected structure indicating that partonic structure in nuclei is different than in free nucleons. This phenomenon is commonly referred to as the EMC effect. Recent Jefferson Lab experimental data showed that the slope of the EMC effect in the 0.3 < xB > 0.7 region scales as the local nuclear density rather than the average nuclear density. This result lead to the comparison of xB>1 short-range correlation plateaus, also a local density effect, to the magnitude of the EMC effect slopes and a clear linear relation was found. In this talk, I will discuss the EMC effect and the short-range correlation plateaus and what this phenomenological relationship between the two implies.
Date: August 17, 2012
Creator: Higinbotham, Douglas
Partner: UNT Libraries Government Documents Department

Role of nuclear binding in the EMC effect

Description: We present a new derivation of the convolution formula for the contributions of nuclear binding to the structure functions measured in the deep inelastic scattering of leptons from nuclei. The derivation, which is manifestly covariant, gives a new binding correction. This new correction, which depends on the mass of the recoiling nucleon fragments, gives corrections that are numerically significant, and that improve the agreement between theory and experiment at large x. We conclude that nuclear binding effects may be sufficient to explain the European-Muon-Collaboration effect at large x.
Date: October 1, 1991
Creator: Gross, Franz & Gross, Franz
Partner: UNT Libraries Government Documents Department

Nuclear effects in deep inelastic scattering

Description: The authors extend the approach used to treat quasi-elastic inclusive electron-nucleus scattering to the deep inelastic region. They provide a general approach to describe lepton scattering from an off-shell nucleon, and calculate the ratio of inclusive deep inelastic scattering cross sections to the deuteron for nuclear matter and helium (EMC-effect). They find that the consistent inclusion of the binding effects, in particular the ones arising from the short-range nucleon-nucleon interaction, allows to describe the data in the region of x > 0.15 where binding fully accounts for the deviation of the cross section ratios from one.
Date: March 1, 1998
Creator: Benhar, O.; Pandharipande, V.R. & Sick, I.
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

Extraction of the ratio of the neutron to proton structure functions from deep inelastic scattering

Description: The authors study the nuclear (A) dependence of the European Muon Collaboration (EMC) effect at high values of x (x {>=} 0.6). Their approach makes use of conventional nuclear degrees of freedom within the Relativistic Impulse Approximation. By performing a non-relativistic series expansion they demonstrate that relativistic corrections make a substantial contribution to the effect at x {approx_gt} 0.6$ and show that the ratio of neutron to proton structure functions extracted from a global fit to all nuclei is not inconsistent with values obtained from the deuteron.
Date: June 1, 1995
Creator: Liuti, S. & Gross, F.
Partner: UNT Libraries Government Documents Department

Constraints on the large-x d/u ratio from electron--nucleus scattering at x>1

Description: Recently the ratio of neutron to proton structure functions F{sub 2}{sup n}/F{sub 2}{sup p} was extracted from a phenomenological correlation between the strength of the nuclear EMC effect and inclusive electron-nucleus cross section ratios at x > 1. Within conventional models of nuclear smearing, this 'in-medium correction' (IMC) extraction constrains the size of nuclear effects in the deuteron structure functions, from which the neutron structure function F{sub 2}{sup n} is usually extracted. The IMC data determine the resulting proton d/u quark distribution ratio, extrapolated to x = 1, to be 0.23 {+-} 0.09 with a 90% confidence level. This is well below the SU(6) symmetry limit of 1/2 and significantly above the scalar diquark dominance limit of 0.
Date: December 1, 2011
Creator: O. Hen, A. Accardi, W. Melnitchouk and E. Piasetzky
Partner: UNT Libraries Government Documents Department

Physics Division annual report 2004.

Description: This report highlights the research performed in 2004 in the Physics Division of Argonne National Laboratory. The Division's programs include operation of ATLAS as a national user facility, nuclear structure and reaction research, nuclear theory, medium energy nuclear research and accelerator research and development. The intellectual challenges of this research represent some of the most fundamental challenges in modern science, shaping our understanding of both tiny objects at the center of the atom and some of the largest structures in the universe. A great strength of these efforts is the critical interplay of theory and experiment. Notable results in research at ATLAS include a measurement of the charge radius of He-6 in an atom trap and its explanation in ab-initio calculations of nuclear structure. Precise mass measurements on critical waiting point nuclei in the rapid-proton-capture process set the time scale for this important path in nucleosynthesis. An abrupt fall-off was identified in the subbarrier fusion of several heavy-ion systems. ATLAS operated for 5559 hours of research in FY2004 while achieving 96% efficiency of beam delivery for experiments. In Medium Energy Physics, substantial progress was made on a long-term experiment to search for the violation of time-reversal invariance using trapped Ra atoms. New results from HERMES reveal the influence of quark angular momentum. Experiments at JLAB search for evidence of color transparency in rho-meson production and study the EMC effect in helium isotopes. New theoretical results include a Poincare covariant description of baryons as composites of confined quarks and non-point-like diquarks. Green's function Monte Carlo techniques give accurate descriptions of the excited states of light nuclei and these techniques been extended to scattering states for astrophysics studies. A theoretical description of the phenomena of proton radioactivity has been extended to triaxial nuclei. Argonne continues to lead in the development and exploitation ...
Date: April 6, 2006
Creator: Glover, J.
Partner: UNT Libraries Government Documents Department

Bound Nucleon Form Factors, Quark-Hadron Duality, and the Nuclear EMC Effect

Description: We discuss the electromagnetic form factors, axial form factors, and structure functions of a nucleon bound in the quark-meson coupling (QMC) model. Free space nucleon form factors are calculated using the improved cloudy bag model (ICBM). After describing finite nuclei and nuclear matter in the quark-based (EMC) model, the in-medium modification of the bound nucleon form factors is calculated in the same model. Finally, the bound nucleon structure function, F2, is extracted using the calculated in-medium electromagnetic form factors and Bloom-Gilman (quark-hadron) duality.
Date: September 13, 2002
Creator: Tsushima, K.; Lu, D.H.; Melnitchouk, W.; Saito, K. & Thomas, A.W.
Partner: UNT Libraries Government Documents Department

An overview of the SLAC results

Description: The history of nucleon spin-structure measurements goes back to the early days of inelastic electron scattering at SLAC, when Vernon Hughes came with a proposal to accelerate polarized electrons to high energy and to study inelastic scattering from a polarized proton target. The quark model of the proton was new at the time, and the spin-dependent structure functions were an excellent testing ground for that model. The proposal developed into an experiment which became SLAC experiment E80. Subsequent experiments followed those early studies, leading to E130 at SLAC, then EMC at CERN, and a host of later experiments. In 1988 the EMC Collaboration published the first data to reach low x. The asymmetries EMC observed fell below quark model expectations, and the experimentally measured proton sum rule indicated that the spin of the quarks contributed little to the proton spin. The subject of nucleon spin-dependent structure functions was stimulated by this surprising result from EMC. The continuation of the spin-structure studies at SLAC, which have been very active in recent years, was stimulated by the successful development of high-intensity beams of polarized electrons. Table 1 lists the past, present, and planned programs and experiments that grew out of the early work. The rest of the report is divided into the following topics: polarized electrons; polarimetry; the SLAC spectrometers; radiative corrections; the proton measurements; neutron targets; the deuterium and {sup 3}He data; the g{sub 2} structure function; and the 50 GeV upgrade of the SLC.
Date: March 1, 1996
Creator: Prescott, C.Y.
Partner: UNT Libraries Government Documents Department

Testing quantum chromodynamics in electroproduction

Description: The exclusive channels in electroproduction are discussed. The study of color transparency, the formation zone, and other novel aspects of QCD by measuring exclusive reactions inside nuclear targets is covered. Diffractive electroproduction channels are discussed, and exclusive nuclear processes in QCD are examined. Non-additivity of nuclear structure functions (EMC effect) is also discussed, as well as jet coalescence in electroproduction. (LEW)
Date: May 1, 1987
Creator: Brodsky, S.J.
Partner: UNT Libraries Government Documents Department

Quark structure functions measured with the Drell-Yan process

Description: The physics relevant to showing that the Drell-Yan process offers the possibility for measuring flavor specific quark momentum distributions of free hadrons and their possible modification in nuclei are presented. The case for flavor specific measurements via use of the Drell-Yan process is developed. 21 refs. (LEW)
Date: January 1, 1986
Creator: Garvey, G.T.
Partner: UNT Libraries Government Documents Department

Measuring strangeness matrix elements of the nucleon

Description: Experiments are proposed to measure various strangeness matrix elements of the nucleon. Examples are electro- and neutrino- production of phi mesons and the difference between neutrino and antineutrino scattering from isospin zero targets, e.g., deuterons.
Date: December 31, 1991
Creator: Henley, E. M.; Pollock, S. J.; Krein, G. & Williams, A. G.
Partner: UNT Libraries Government Documents Department

The classical EMC effect from few-body systems to nuclear matter: Can binding effects explain it?

Description: It is shown that if the effects of nucleon binding on deep inelastic scattering are considered within many-body realistic descriptions of nuclei which include nucleon-nucleon correlations, the EMC effect in light and medium weight nuclei and nuclear matter can be accounted for in the region 0.2 {le} x {le} 0.5, but a systematic discrepancy between theory and experiment remains to be explained for 0.5 {le} x {le} 0.9.
Date: May 14, 1991
Creator: Ciofi degli Atti, C. & Liuti, S.
Partner: UNT Libraries Government Documents Department

Results from FNAL E745 on neutrino-nucleus interactions (EMC effect and hadron formation)

Description: The dark tracks (stubs) in high energy neutrino-nucleus interactions in the Tohoku High Resolution Freon Bubble Chamber are investigated. Classifying events into groups by using the dark tracks, correlations between the dark track production and neutrino interactions are studied. Events without dark tracks comprise a reasonable sample of events which occurred on quasi-free nucleons inside nucleus. By comparing the groups using the no dark track group as a comparison sample instead of neutrino-deuterium events, the EMC effect and hadron formation are investigated. This method provides new results which differ somewhat from the conventional data for the EMC effect and formation-rescattering. 10 refs., 17 figs.
Date: January 1, 1989
Creator: Kitagaki, T. (Tohoku Univ., Sendai (Japan). Bubble Chamber Physics Lab.)
Partner: UNT Libraries Government Documents Department

Deep inelastic muon scattering with hadron detection

Description: The physics motivation and experimental apparatus of FNAL E665 are described. E665 is a new experiment to study the hadrons in coincidence with muons deep inelastically scattered from nuclei. One of the goals of the experiment is to examine nuclear medium effects not only on the baryon quark distributions (the EMC effect) but also on the process of hadronization in high energy collisions. 17 refs., 5 figs.
Date: January 1, 1985
Creator: Geesaman, D.F. & Green, M.C.
Partner: UNT Libraries Government Documents Department

Electromagnetic structure of nuclei

Description: A brief review is given of selected topics in the electromagnetic structure of nucleons and nuclei, including nucleon form factors from both quantum chromodynamics and electron scattering data, measurements of the deuteron and triton form factors, quasi-elastic scattering, and the EMC effect. 47 refs., 13 figs. (LEW)
Date: July 1, 1986
Creator: Arnold, R.G.
Partner: UNT Libraries Government Documents Department

Nuclear-like states of quark matter

Description: In a world with only one flavor of light quark, QCD suggests that the low energy states of quark matter are similar to nuclei, but are not well represented as collections of baryons. Except for the existence of open nucleon channels, the same would be true for the actual, two-light-flavor world. 3 refs.
Date: January 1, 1986
Creator: Goldman, T.; Schmidt, K.E. & Stephenson, G.J. Jr.
Partner: UNT Libraries Government Documents Department

High energy nuclear quasielastic reactions: Decisive tests of nuclear binding/pion models of the EMC effect

Description: The light-cone nucleon momentum distributions obtained from non- relativistic spectral functions or given by nuclear binding/pion models are often used to analyze high Q{sup 2} quasi-elastic and deep-inelastic (e,e{prime}) reactions. We demonstrate that in such models the presence of non-nucleonic components causes the scattering from forward and backward moving target protons to be significantly different. Other models do not have this property. The sensitivity of current (e,e{prime}p) and (p,pp) color transparency experiments is sufficient to observe these differences.
Date: January 1, 1991
Creator: Frankfurt, L; Strikman, M & Miller, G A
Partner: UNT Libraries Government Documents Department

EMC effect

Description: A review is presented of data and theoretical interpretations of the nuclear dependence of quark and antiquark distributions as observed in the deep inelastic scattering of neutrinos and charged leptons from nuclei. After a summary of the experimental situation and a survey of proposed explanations, the author concentrates on interpretations in terms of conventional nuclear physics and on the Q/sup 2/-rescaling approach. The review concludes with a list of desirable future experiments. 32 refs., 5 figs.
Date: September 1, 1986
Creator: Berger, E. L.
Partner: UNT Libraries Government Documents Department

Spin physics in the next decade

Description: The author`s personal opinion is that the fascinating field of nonperturbative QCD will be led by polarized beam experiments. He focuses on two developments which will surely produce a wealth of new physics within the next ten years. These are polarized colliding beams, and polarized jet targets in conjunction with polarized beams in storage rings. In order to make the overview manageable, he covers only selected areas where the physics goals are the elucidation of nonperturbative aspects of QCD applied to nucleons and nuclei. He discusses several areas of polarized structure function physics which will be feasible in the next 5--10 years.
Date: December 1, 1994
Creator: Moss, J. M.
Partner: UNT Libraries Government Documents Department