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R. M. Davidson

Publications and source records attributed to R. M. Davidson.

13 recordsLinked to original sources
arXiv2001

Parton Distributions Functions of Pion, Kaon and Eta pseudoscalar mesons in the NJL model

Parton distributions of pseudoscalar pi,K and eta mesons obtained within the NJL model using the Pauli-Villars regularization method are analyzed in terms of LO and NLO evolution, and the valence sea quark and gluon parton distributions for the pion are obtained at Q^2 = 4 GeV^2 and compared to existing parametrizations at that scale. Surprisingly, the NLO order effects turn out to be small compared to the LO ones. The valence distributions are in good agreement with experimental analyses, but the gluon and sea distributions come out to be softer in the high-x region and harder in the low-x region than the experimental analyses suggest.

hep-ph↗
arXiv2001

Multipole Analysis of a Benchmark Data Set for Pion Photoproduction

We have fitted low- and medium-energy benchmark datasets employing methods used in the MAID/SAID and dynamical model analyses. Independent fits from the Mainz, RPI, Yerevan, and Kharkov groups have also been performed over the low-energy region. Results for the multipole amplitudes are compared in order to gauge the model-dependence of such fits, given identical data and a single method for error handling.

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arXiv2001

Effect of form factors in fits to photoproduction data

We compare the effects of several form factor recipes in fits to pseudoscalar meson photoproduction data. The specific examples of pion and kaon photoproduction are used to illustrate how different choices can alter the results of such analyses.

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arXiv2001

Form factors and photoproduction amplitudes

We examine the use of phenomenological form factors in tree level amplitudes for meson photoproduction. Two common recipes are shown to be fundamentally incorrect. An alternate form consistent with gauge invariance and crossing symmetry is proposed.

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arXiv1999

The Role of the D13 (1520) Resonance in eta Electroproduction

We investigate the electroproduction of eta mesons below a center of momentum energy of 1.6 GeV, with particular emphasis on the roles of the N*(1535) and N*(1520) resonances. Using the effective Lagrangian approach, we show that the transverse helicity amplitude of the N*(1535) can be extracted with good accuracy from the new eta electroproduction data, under reasonable assumptions for the strength of the longitudinal helicity amplitude. In addition, although the differential cross section is found to to have a small sensitivity to the N*(1520) resonance, it is shown that a recently completed double polarization experiment is very sensitive to this resonance.

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arXiv1998

Problems with Extraction of the Nucleon to Delta(1232) Photonic Amplitudes

We investigate the model dependence and the importance of choice of database in extracting the {\it physical} nucleon-Delta(1232) electromagnetic transition amplitudes, of interest to QCD and baryon structure, from the pion photoproduction observables. The model dependence is found to be much smaller than the range of values obtained when different datasets are fitted. In addition, some inconsistencies in the current database are discovered, and their affect on the extracted transition amplitudes is discussed.

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arXiv1997

Precision Theorectical Tests of Effective Lagrangians: Pion Photoproduction from Threshold Through the Delta Resonance

We shall review here our current knowledge and new frontiers of the pion photoproduction study, from threshold through the Delta resonance region, emphasizing the hadron physics program, of interest to a 250 MeV, high duty factor electron facility, such as the upgraded MAX-lab at the Lund University, Sweden, where it would be possible to produce tagged photons of high quality, with energy below approximately 200 MeV.

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arXiv1997

An Estimate of Charge Symmetry Breaking in Nuclear Deep Inelastic Scattering

We estimate the magnitude of charge symmetry breaking effects in deep inelastic scattering from nuclei. The resulting contribution to systematic uncertainties in hadronic determinations of $sin^2θ_W$ are found to be less than the current experimental accuracy, but may be important in the analyses of more precise future experiments. We expect the largest nuclear charge symmetry breaking effects in the Paschos-Wolfenstein ratio $R^-$, where the resulting uncertainty in the determination of $sin^2 θ_W$ reaches $10^{-3}$.

hep-ph↗
arXiv1996

Sidewise dispersion relations and the structure of the nucleon vertex

We revisit sidewise dispersion relations as a method to relate the nucleon off-shell form factor to observable quantities, namely the meson-nucleon scattering phase shifts. It is shown how for meson-nucleon scattering a redefinition of the intermediate fields leaves the scattering amplitude invariant, but changes the behavior of the off-shell form factor as expressed through dispersion relations, thus showing representation dependence. We also employ a coupled-channel unitary model to test the validity of approximations concerning the influence of inelastic channels in the sidewise dispersion relation method.

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arXiv1995

Analysis of the Low-Energy Theorem for γp \to p π^0

The derivation of the `classical' low-energy theorem (LET) for γp \rightarrow pπ^0 is re-examined and compared to chiral perturbation theory. Both results are correct and are not contradictory; they differ because different expansions of the same quantity are involved. Possible modifications of the extended partially conserved axial-vector current relation, one of the starting points in the derivation of the LET, are discussed. An alternate, more transparent form of the LET is presented.

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