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in creator/contributor: "Thomas, A. W."

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Note on Nuclear Shadowing at Low Q{sup 2} and the Extraction of sin{sup 2} theta{sub w}

In the light of a recent claim that models of nuclear shadowing which incorporate a vector meson dominance component at low Q{sup 2} are incompatible with nuclear deep inelastic scattering data, we compare the predictions of such a model with high precision data on the Q{sup 2} dependence of nuclear shadowing. Contrary to this claim, we find that models which incorporate both vector meson and partonic mechanisms are indeed consistent with both the magnitude and the Q{sup 2} slope of the shadowi… more

Date: August 1, 2002

Creator: Melnitchouk, Wally & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Mesonic contributions to the spin and flavor structure of the nucleon

Since its initial investigation at SLAC in the late 60's, deep inelastic lepton scattering has provided a wonderful tool to explore perturbative QCD and to test many features of the Standard Model. The crucial theoretical tools needed to understand deep-inelastic scattering, namely the operator product expansion and the renormalization group (which are now used throughout particle physics), were developed in parallel with the data taking. Using these techniques one can often eliminate the need … more

Date: February 1, 1996

Creator: Speth, J. & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Deep Inelastic Scattering from Light Nuclei

We review recent developments in the study of deep inelastic scattering from light nuclei, focusing in particular on deuterium, helium, and lithium nuclei. Understanding the nuclear effects in these systems is essential for the extraction of information on the neutron structure function.

Date: April 1, 2002

Creator: Melnitchouk, Wally & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Moments of Isovector Quark Distributions in Lattice QCD

We investigate the connection of lattice calculations of moments of isovector parton distributions to the physical regime through extrapolations in the quark mass. We consider the one pion loop renormalization of the nucleon matrix elements of the corresponding operators and thereby develop formulae with which to extrapolate the moments of the unpolarized, helicity and transversity distributions. There formulae are consistent with chiral perturbation theory in the chiral limit and incorporate t… more

Date: June 1, 2002

Creator: Detmold, W.; Melnitchouk, Wally & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Moments of Isovector Quark Distributions from Lattice QCD

We present a complete analysis of the chiral extrapolation of lattice moments of all twist-2 isovector quark distributions, including corrections from N[pi] and [Delta][pi] loops. Even though the [Delta] resonance formally gives rise to higher order non-analytic structure, the coefficients of the higher order terms for the helicity and transversity moments are large and cancel much of the curvature generated by the wave function renormalization. The net effect is that, whereas the unpolarized m… more

Date: September 1, 2002

Creator: Detmold, W.; Melnitchouk, Wally & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Parton distributions from lattice QCD

We extract the x dependence of the nonsinglet u-d distribution function in the nucleon from the lowest few moments calculated on the lattice, using an extrapolation formula which ensures the correct behavior in the chiral and heavy quark limits. We discuss the implications for the quark mass dependence of meson masses lying on the J(PC)=1(--) Regge trajectory.

Date: August 1, 2001

Creator: Detmold, W.; Melnitchouk, W. & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Quark-hadron duality and the nuclear EMC effect

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… more

Date: November 1, 2001

Creator: Melnitchouk, W.; Tsushima, K. & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Connecting Structure Functions on the Lattice with Phenomenology

We examine the extraction of moments of parton distributions from lattice data, focusing in particular on the chiral extrapolation as a function of the quark mass. Inclusion of the correct chiral behavior of the spin-averaged isovector distribution resolves a long-standing discrepancy between the lattice moments and experiment. We extract the x-dependence of the valence u-d distribution from the lowest few lattice moments, and discuss the implications for the quark mass dependence of meson mass… more

Date: December 1, 2001

Creator: Detmold, W.; Melnitchouk, W. & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Dynamical symmetry breaking in the sea of the nucleon

The authors derive the non-analytic chiral behavior of the flavor asymmetry dbar - ubar. Such behavior is a unique characteristic of Goldstone boson loops in chiral theories, including QCD, and establishes the unambiguous role played by the Goldstone boson cloud in the sea of the proton. Generalizing the results to the SU(3) sector, they show that strange chiral loops require that the s - sbar distribution be non-zero.

Date: May 1, 2000

Creator: Thomas, A. W.; Melnitchouk, W. & Steffens, F. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

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

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 QC… more

Date: November 1, 1999

Creator: Melnitchouki, W.; Afnan, I. R.; Bissey, F. & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

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

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 calculate… more

Date: September 13, 2002

Creator: Tsushima, K.; Lu, D. H.; Melnitchouk, W.; Saito, K. & Thomas, A. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

A New Slant on Hadron Structure

Rather than regarding the restriction of current lattice QCD simulations to quark masses that are 5--10 times larger than those observed, we note that this presents a wonderful opportunity to deepen our understanding of QCD. Just as it has been possible to learn a great deal about QCD by treating N{sub c} as a variable, so the study of hadron properties as a function of quark mass is leading us to a much deeper appreciation of hadron structure. As examples we cite recent progress in using the c… more

Date: December 1, 2000

Creator: Detmold, W.; Melnitchouk, W.; Leinweber, D. B.; Thomas, A. W. & Wright, S. V.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Neutron structure function and A=3 mirror nuclei

The authors demonstrate that the free neutron structure function can be extracted in deep-inelastic scattering from A=3 mirror nuclei, with nuclear effects canceling to within 2% for x {approx_lt} 0.85.

Date: June 1, 2000

Creator: Afnan, I. R.; Bissey, F.; Gomez, J.; Katramatou, A. T.; Melnitchouk, W.; Petratos, G. G. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

FLIC Fermions and Hadron Phenomenology

A pedagogical overview of the formulation of the Fat Link Irrelevant Clover (FLIC) fermion action and its associated phenomenology is described. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative order (a) improvement where near-continuum results are obtained at finite lattice spacing. Spin-1/2 and spin-3/2, even and odd parity baryon resonances are investigated in quenched QCD, where the nature of the Roper resonance and Lambda (1405) are of particular interest.… more

Date: June 1, 2002

Creator: Leinweber, D.; Hedditch, J. N.; Melnitchouk, W.; Thomas, A. W.; Williams, A. G.; Young, R. D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department