arXiv subjects

R. A. Arndt

Publications and source records attributed to R. A. Arndt.

54 records · Page 3Linked to original sources

arXiv2000

Measurement of the Cross Section Asymmetry of the Reaction gp-->pi0p in the Resonance Energy Region Eg = 0.5 - 1.1 GeV

The cross section asymmetry Sigma has been measured for the photoproduction of pi0-mesons off protons, using polarized photons in the energy range Eg = 0.5 - 1.1 GeV. The CM angular coverage is Theta = 85 - 125 deg with energy and angle steps of 25 MeV and 5 deg, respectively. The obtained Sigma data, which cover the second and third resonance regions, are compared with existing experimental data and recent phenomenological analyses. The influence of these measurements on such analyses is also considered.

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arXiv1999

New Result for the Pion-Nucleon Sigma Term from an Updated VPI/GW Pion-Nucleon Partial-Wave and Dispersion Relation Analysis

A new result for the nucleon sigma term from an updated pion-nucleon partial-wave and dispersion relation analysis of the Virginia Polytechnic Institute (now George Washington University) group is discussed. Using a method similar to that of Gasser, Leutwyler, Locher, and Sainio, we obtain Sigma=90 +/- 8 MeV (preliminary), in disagreement with the canonical result 64 +/- 8 MeV, but consistent with expectations based on new information on the $π$NN coupling constant, pionic atoms, and the Delta resonance width.

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arXiv1999

Extraction of the D13(1520) photon-decay couplings from pion- and eta-photoproduction data

We compare results for the D13(1520) photon-decay amplitudes determined in analyses of eta- and pion-photoproduction data. The ratio of helicity amplitudes (A_3/2 / A_1/2), determined from eta-photoproduction data, is quite different from that determined in previous analyses of pion-photoproduction data. We consider how strongly the existing pion-photoproduction data constrain both this ratio and the individual photon-decay amplitudes.

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arXiv1999

Determination of the Pion-Nucleon Coupling Constant in the VPI/GW Pion-Nucleon Elastic Scattering Partial Wave and Dispersion Relation Analyis

Our extraction of the pion-nucleon coupling constant from πp elastic scattering data is outlined. A partial wave analysis (T_π < 2100 MeV) is performed simultaneously with a fixed-t dispersion relation analysis (T_π < 800 MeV). The πNN coupling constant g^2/4πis searched to find the best fit. The result 13.73 \pm 0.01 \pm 0.07 (first error statistical, second systematic) is found to be insensitive to database changes and Coulomb barrier corrections. This value satisfies important elements of low energy QCD like the Goldberger-Treiman discrepancy, the Dashen-Weinstein sum rule, and chiral perturbation theory predictions of threshold pion photoproduction.

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arXiv1999

Sensitivity to the pion-nucleon coupling constant in partial-wave analyses of elastic pi-N and NN scattering and pion photoproduction

We summarize results obtained in our studies of the pion-nucleon coupling constant. Several different techniques have been applied to pi-N and NN elastic scattering data, and the existing database for single-pion photoproduction. The most reliable determination comes from pi-N elastic scattering. The sensitivity in this reaction was found to be greater, by at least a factor of 3, when compared with analyses of NN elastic scattering or single-pion photoproduction.

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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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arXiv1998

Elastic scattering analyses and dispersion relation constraints

We present the results of energy-dependent and single-energy partial-wave analyses of pi-N elastic scattering data with laboratory kinetic energies below 2.1 GeV. We have considered the effect of adding dispersion-relation constraints required for a more reliable extraction of the pi-N sigma term. The results of these new fits are compared with those generated previously, using a reduced set of constraints, and with a fit which has only utilized forward constraints associated with the S-wave scattering lengths. We compare the results in terms of their resonance spectra and preferred values for the pi-N-N coupling and pi-N sigma term.

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arXiv1998

The energies and residues of the nucleon resonances N(1535) and N(1650)

We extract pole positions for the N(1535) and N(1650) resonances using two different models. The positions are determined from fits to different subsets of the existing $πN\toπN$, $πN\toηN$ and $γp\toηp$ data and found to be 1515(10)--i85(15)MeV and 1660(10)--i65(10)MeV, when the data is described in terms of two poles. Sensitivity to the choice of fitted data is explored. The corresponding $ππ$ and $ηη$ residues of these poles are also extracted.

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arXiv1997

Nucleon-Nucleon Partial Wave Analysis to 2.5 GeV

A partial-wave analysis of NN elastic scattering data has been completed. This analysis covers an expanded energy range, from threshold to a laboratory kinetic energy of 2.5 GeV, in order to include recent elastic pp scattering data produced by the EDDA collaboration at COSY. The results of both single-energy and energy-dependent analyses are described.

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arXiv1997

Analysis of Pion Photoproduction over the Delta Resonance Region

A number of recent multipole analyses from Mainz, RPI, BNL and Virginia Tech (VPI) have focused on the first resonance region. One goal common to these studies was an improved set of Delta(1232) photo-decay amplitudes. There has been considerable debate over the differing results found for A(1/2), A(3/2) and the E2/M1 ratio. We show that a much more consistent set of values is possible if differences in the database are considered.

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arXiv1997

Nucleon-nucleon elastic scattering analysis to 2.5 GeV

A partial-wave analysis of NN elastic scattering data has been completed. This analysis covers an expanded energy range, from threshold to a laboratory kinetic energy of 2.5 GeV, in order to include recent elastic pp scattering data from the EDDA collaboration. The results of both single-energy and energy-dependent analyses are described.

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arXiv1997

Pion photoproduction in the delta resonance region

We have updated our multipole analyses to incorporate new data from the low-energy and delta resonance regions. We note a slight decrease in our estimate of the delta photo-decay amplitudes. This agrees with results found in Compton scattering. Our values are also in good agreement with a previous RPI determination. We have reexamined our determinations of the E2/M1 ratio at the resonance energy and at the pole. We find an E2/M1 ratio (at the pole) which is in good agreement with recent the Mainz value.

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arXiv1997

Comment on `Measurement of the $π^+ \vec p$ analyzing power at 68.3 MeV'

We comment on a recent paper by Weiser et al. [Phys. Rev. C {\bf 54}, 1930 (1996)]. The authors have performed a single-energy analysis of $π^+ p$ scattering data at 68.3 MeV, finding a value for the $S_{31}$ phase shift about 1^o smaller than found in the Karlsruhe-Helsinki (KH) partial-wave analysis. The authors use this result to argue for a dispersion relation analysis using recently measured data, so that their effect on the $πNN$ coupling constant (f^2) and $Σ$ amplitude can be determined. We note that these tasks were accomplished prior to the submission of the above paper. We clarify the effect of this new analyzing power data on f^2 and the $Σ$ amplitude.

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arXiv1997

Combined analysis of the reactions $pp \to pp$, $πd\to πd$, and $πd\to pp$

Results are presented for a combined analysis of the reactions $pp\to pp$, $πd\to πd$ and $πd\to pp$ over the $\sqrt{s}$ interval from pion threshold to approximately 2.4 GeV. These results for $πd\to pp$ and $πd$ elastic scattering are superior to our previous analyses of these reactions. In particular, the overall phase in $πd\to pp$ has now been determined. Comparisons are made with previous (separate and combined) analyses of this two-nucleon system.

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arXiv1996

Influence of spin-rotation measurements on partial-wave analyses of elastic pion-nucleon scattering

Recent measurements of spin-rotation parameters in elastic $π^+ p$ scattering are in marked disagreement with predictions of the Carnegie-Mellon$-$Berkeley and Karlsruhe-Helsinki analyses. Using the method of Barrelet, we show how this discrepancy can be removed. We then show how this Barrelet transformation alters the partial-wave amplitudes. The effect of unitarity and analyticity constraints is also considered.

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arXiv1995

Updated resonance photo-decay amplitudes to 2 GeV

We present the results of an energy-dependent and set of single-energy partial-wave analyses of single-pion photoproduction data. These analyses extend from threshold to 2 GeV in the laboratory photon energy, and update our previous analyses to 1.8 GeV. Photo-decay amplitudes are extracted for the baryon resonances within this energy range. We consider two photoproduction sum rules and the contributions of two additional resonance candidates found in our most recent analysis of $πN$ elastic scattering data. Comparisons are made with previous analyses.

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arXiv1995

Extraction of the $πNN$ coupling constant from NN scattering data

We reexamine Chew's method for extracting the $πNN$ coupling constant from np differential cross section measurements. Values for this coupling are extracted below 350 MeV, in the potential model region, and up to 1 GeV. The analyses to 1~GeV have utilized 55 data sets. We compare these results to those obtained via $χ^2$ mapping techniques. We find that these two methods give consistent results which are in agreement with previous Nijmegen determinations.

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arXiv1995

Updated analysis of $π$N elastic scattering data to 2.1~GeV: The Baryon Spectrum

We present the results of energy-dependent and single-energy partial-wave analyses of $π$N elastic scattering data with laboratory kinetic energies below 2.1~GeV. Resonance structures have been extracted using Breit-Wigner fits, speed plots, and a complex plane mapping of the associated poles and zeroes. This is the first set of resonance parameters from a VPI analysis constrained by fixed-t dispersion relations. We have searched our solutions for structures which may have been missed in our previous analyses, finding candidates in the $S_{11}$ and $F_{15}$ partial-wave amplitudes. Our results are compared with those found by the Karlsruhe, Carnegie-Mellon$-$Berkeley, and Kent State groups.

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