Searcharxiv⌕ Search

arXiv subjects

I. I. Strakovsky

Publications and source records attributed to I. I. Strakovsky.

At least 127 records · Page 7Linked to original sources

Nucleon and Hyperon Resonances with the Crystal Ball

The Crystal Ball Spectrometer is being used at Brookhaven National Laboratory in a series of experiments which study all neutral final states of pi-p and K-p induced reactions. We report about the experimental setup and progress in obtaining new results for the radiative capture reactions pi-p-->gn and K-p-->gL,charge exchange pi-p-->pi0n,two pi0 production pi-p-->pi0pi0n, and eta production pi-p-->eta n reactions. Data have also been obtained on the decays of N*, Delta, Lambda, and Sigma resonances. Threshold eta production has been studied in detail for both pi-p and K-p. Sequential resonance decays have been investigated bystudying the 2pi0 production mechanism both in the fundamental interaction and in nuclei. In addition, we have used the etas produced near threshold to make precision measurements searching in particular for rare and forbidden eta decays.

nucl-ex↗

Effect of double-polarization data in fits to single-pion photoproduction

We investigate the influence of new Jefferson Lab polarization-transfer data, Cx and Cz, and recoil polarization, Py, measurements in multipole fits to the single-pion photoproduction database. Results are compared to those found with the addition of a double-polarization quantity associated with the Gerasimov- Drell-Hearn sum rule.

nucl-th↗

Photoproduction of Pseudoscalar Mesons

Experiments that study the photoproduction of pseudoscalar mesons; pions, etas and kaons, have the potential to increase our knowledge of baryon and hyperon resonance properties. Recent experiments at JLab, Mainz, GRAAL, and Bonn are beginning to produce results in the form of polarization and asymmetry measurements and determinations of the differential and integrated cross sections. These new data are essential to the performance of Partial-Wave Analyses that are less model dependent and coupled-channels calculations that incorporate unitarity dynamically,combining hadronic reaction channels together with electromagnetic processes. This approach is necessary to extract resonance properties and may lead to the identification of missing, but predicted, resonances. Some recent experimental and phenomenological results for single and double pseudoscalar meson photoproduction are discussed.

nucl-ex↗

SAID Results for GDH-Related Sum Rules

Model-dependence of the single-pion contribution to the GDH, Baldin, and forward spin-polarizability sum rules is explored, using the most recent SAID multipole analysis. Results from SAID and MAID are compared.

nucl-th↗

Dispersion relation analysis of neutral pion photo- and electroproduction at threshold using the MAID and SAID solutions

Neutral pion photo- and electroproduction at threshold is analyzed in the framework of dispersion relations. For this purpose, we evaluate the real threshold amplitudes in terms of Born contributions and dispersion integrals determined by the imaginary parts of the MAID and SAID multipoles. The results show considerable cancellations between Born terms and resonance contributions. Good agreement with the data is found for photoproduction. While our dispersion analysis suggests considerable discrepancies for electroproduction, the present state of the experimental multipole analysis at finite Q^2 does not permit drawing conclusions at this time.

nucl-th↗

Analysis of Pion Photoproduction Data

A partial-wave analysis of single-pion photoproduction data has been completed. This study extends from threshold to 2 GeV in the laboratory photon energy, focusing mainly on the influence of new measurements and model-dependence in the choice of parameterization employed above the two-pion threshold. Results are used to evaluate sum rules and estimate resonance photo-decay amplitudes. These are compared to values obtained in the MAID analysis.

nucl-th↗

The pion-nucleon Sigma term is definitely large: results from a G.W.U. analysis of pion nucleon scattering data

A new result for the pion nucleon Sigma term from a George Washington University/TRIUMF group analysis of pion nucleon data is presented. The value Sigma=79$\pm$7 MeV was obtained, compared to the canonical value 64$\pm$8 MeV found by Koch. The difference is explained simply by the PSI pionic hydrogen value for a(pi -p), the latest results for the $πNN$ coupling onstant, and a narrower Delta resonance. Many systematic effects have been investigated, including Coulomb corrections, and database changes, and our results are found to be robust. In the standard interpretation, our value of Sigma implies a nucleon strangeness fraction y/2~0.23. The implausibility of such a large strange component suggests that the relationship between Sigma and nucleon strangeness ought to be re-examined.

hep-ph↗

Analysis of Pion Electroproduction Data

A fit to the existing pion electroproduction data is presented. This work builds upon our previous analyses of pion photoproduction and elastic pion-nucleon scattering over the Delta resonance region. We comment on the extraction of E_1+ ^3/2 / M_1+ ^3/2 (E2/M1) and S_1+ ^3/2 / M_1+ ^3/2 (S2/M1) ratios, and note that the E2/M1 ratio approaches, and possibly crosses, zero below a Q2 of 5 (GeV/c}^2.

nucl-th↗

Charge-Symmetry Violation in Pion Scattering from Three-Body Nuclei

We discuss the experimental and theoretical status of charge-symmetry violation (CSV) in the elastic scattering of pi+ and pi- on 3H and 3He. Analysis of the experimental data for the ratios r1, r2, and R at Tpi = 142, 180, 220, and 256 MeV provides evidence for the presence of CSV. We describe pion scattering from the three-nucleon system in terms of single- and double-scattering amplitudes. External and internal Coulomb interactions as well as the Delta-mass splitting are taken into account as sources of CSV. Reasonable agreement between our theoretical calculations and the experimental data is obtained for Tpi = 180, 220, and 256 MeV. For these energies, it is found that the Delta-mass splitting and the internal Coulomb interaction are the most important contributions for CSV in the three-nucleon system. The CSV effects are rather sensitive to the choice of pion-nuclear scattering mechanisms, but at the same time, our theoretical predictions are much less sensitive to the choice of the nuclear wave function. It is found, however, that data for r2 and R at Tpi = 142 MeV do not agree with the predictions of our model, which may indicate that there are additional mechanisms for CSV which are important only at lower energies.

nucl-th↗

Precision Pion-Proton Elastic Differential Cross Sections at Energies Spanning the Delta Resonance

A precision measurement of absolute pi+p and pi-p elastic differential cross sections at incident pion laboratory kinetic energies from T_pi= 141.15 to 267.3 MeV is described. Data were obtained detecting the scattered pion and recoil proton in coincidence at 12 laboratory pion angles from 55 to 155 degrees for pi+p, and six angles from 60 to 155 degrees for pi-p. Single arm measurements were also obtained for pi+p energies up to 218.1 MeV, with the scattered pi+ detected at six angles from 20 to 70 degrees. A flat-walled, super-cooled liquid hydrogen target as well as solid CH2 targets were used. The data are characterized by small uncertainties, ~1-2% statistical and ~1-1.5% normalization. The reliability of the cross section results was ensured by carrying out the measurements under a variety of experimental conditions to identify and quantify the sources of instrumental uncertainty. Our lowest and highest energy data are consistent with overlapping results from TRIUMF and LAMPF. In general, the Virginia Polytechnic Institute SM95 partial wave analysis solution describes our data well, but the older Karlsruhe-Helsinki PWA solution KH80 does not.

nucl-ex↗

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.

nucl-ex↗

Charge Symmetry Violation Effects in Pion Scattering off the Deuteron

We discuss the theoretical and experimental situations for charge symmetry violation (CSV) effects in the elastic scattering of pi+ and pi- on deuterium (D) and 3He/3H. Accurate comparison of data for both types of targets provides evidence for the presence of CSV effects. While there are indications of a CSV effect in deuterium, it is much more pronounced in the case of 3He/3H. We provide a description of the CSV effect on the deuteron in terms of single- and double- scattering amplitudes. The Delta-mass splitting is taken into account. Theoretical predictions are compared with existing experimental data for pi-d scattering; a future article will speak to the pi-three nucleon case.

nucl-th↗

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.

nucl-th↗

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.

nucl-th↗

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.

nucl-th↗

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.

nucl-th↗

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.

nucl-th↗

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.

nucl-th↗