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[en] A new generation of complete experiments is currently underway with the goal of performing a high precision extraction of pseudoscalar meson photo-production amplitudes. Here we review the most general analytic form of the cross section, dependent upon the three polarization vectors of the beam, target and recoil baryon, including all single, double and triple-polarization terms involving 16 spin-dependent observables. Analytic expressions that determine the recoil baryon polarization are also presented. Different conventions are in use in the literature and we have used a numerical calculation of cross sections from Chew-Goldberger-Low-Nambu amplitudes with arbitrary spin projections to clarify apparent sign differences. As an illustration of the use of this machinery, we carry out a multipole analysis of the gammap --> K+Lambda reaction and examine the impact of recently published polarization measurements. In fitting multipoles, we use a combined Monte Carlo sampling of the amplitude space, with gradient minimization, and find a shallow chi2 valley pitted with a very large number of local minima, despite the inclusion of recent data on 8 different observables. We conclude that, while a mathematical solution to the problem of determining an amplitude free of ambiguities may require 8 observables, as has been pointed out in the literature, experiments with realistically achievable uncertainties will require a significantly larger number.

[en] A new generation of over-complete experiments is underway, with the goal of performing a high precision extraction of pseudoscalar meson photo-production amplitudes. Such experimentally determined amplitudes can be used both as a test to validate models and as a starting point for an analytic continuation in the complex plane to search for poles. Of crucial importance for both is the level of uncertainty in the extracted multipoles. We have probed these uncertainties by analyses of pseudo-data for KLambda photoproduction, first for the set of 8 observables that have been published for the K⁺ Lambda channel and then for pseudo-data on a complete set of 16 observables with the uncertainties expected from analyses of ongoing CLAS experiments. In fitting multipoles, we have used a combined Monte Carlo sampling of the amplitude space, with gradient minimization, and have found a shallow X² valley pitted with a large number of local minima. This results in bands of solutions that are experimentally indistinguishable. All ongoing experiments will measure observables with limited statistics. We have found a dependence on the particular random choice of values of Gaussian distributed pseudo-data, due to the presence of multiple local minima. This results in actual uncertainties for reconstructed multipoles that are often considerable larger than those returned by gradient minimization routines such as Minuit which find a single local minimum. As intuitively expected, this additional level of uncertainty decreases as larger numbers of observables are included.

[en] In preparation for a new generation of complete experiments with the goal of performing a high precision extraction of pseudoscalar meson photo-production amplitudes, we present expressions that allow the direct numerical calculation of matrix elements with arbitrary spin projections from Chew-Goldberger-Low-Nambu (CGLN) amplitudes. We use this numerical tool to verify the most general analytic form of the cross section, dependent upon the three polarization vectors of the beam, target and recoil baryon, including all single, double and triple-polarization terms involving 16 spin-dependent observables. Analytic expressions that determine the recoil baryon polarization are presented, together with examples of their potential use with quasi-4? detectors to deduce observables. We assemble the analytic equations relating the 16 experimental observables and the CGLN amplitudes and use our independent method of numerical evaluation to resolve sign differences that exist in the literature.

[en] This presentation reports on the consistent adjustment of nuclear data parameters performed within a BNL-INL collaboration. The main advantage compared to the classical adjustment of multigroup constants is to provide final nuclear data constrained by the nuclear reaction theory and consistent with both differential and integral measurements. The feasibility of a single-isotope assimilation was tested on a few priority materials (²³Na, ⁵⁶Fe, ¹⁰⁵Pd, ^235,238U, ²³⁹Pu) using a selection of clean integral experiments. The multi-isotope assimilation is under study for the Big-3 (^235,238U, ²³⁹Pu). This work shows that a consistent assimilation is feasible, but there are pitfalls to avoid (e.g. non-linearity, cross section fluctuations) and prerequisites (e.g. realistic covariances, good prior, realistic weighting of differential and integral experiments). Finally, only all experimental information combined with the state of the art modelling may provide a 'right' answer

[en] We report new high-precision measurements of p(r vec γ,γ), p(r vec γ,π⁰) and p(r vec γ,π⁺) cross section and beam asymmetry angular distributions for photon beam energies in the range from 213 MeV to 333 MeV. The cross sections for all three channels are locked together with a small common systematic scale uncertainty of 2%. A large overdetermination of kinematic parameters was used to achieve the first complete separation of the Compton scattering and π⁰-production channels. This has also allowed all detector efficiencies for the p(rvec γ,γ) and p(rvec γ,π⁰) channels to be measured directly from the data itself without resorting to simulations. The new Compton results are approximately 30% higher than previous Bonn data near the peak of the Δ resonance, resolving a long-standing unitarity puzzle. However, our p(rvec γ,π⁰) and p(rvec γ,π⁺) cross sections are also about 10% higher than both earlier Bonn data and recent Mainz measurements, while our p(rvec γ,π⁺) cross sections are in good agreement with results from Tokyo. Our polarization asymmetry data are of the highest precision yet available and have considerable impact upon multipole analyses. These new data have been combined with other polarization ratios in a simultaneous analysis of both Compton scattering and π production, with Compton scattering providing two new constraints on the photopion amplitude. This analysis has improved the accuracy in the E2/M1 mixing ratio for the N→Δ transition, EMR=-[3.07±0.26(stat+syst)±0.24(model)](%), and the corresponding N→Δ transverse helicity amplitudes, A_1/2=-[135.7±1.3(stat+syst)±3.7(model)](10^-3GeV^-1/2) and A_3/2=-[266.9±1.6(stat+syst)±7.8(model)](10^-3GeV^-1/2). From these we deduce an oblate spectroscopic deformation for the Δ⁺. The same simultaneous analysis has been used to extract the proton dipole polarizabilities, bar α-bar β=+[10.39±1.77(stat+syst)_-1.87^+1.02(model)](10^-4fm³) in agreement with previous low energy measurements, and bar α+bar β=+[13.25±0.86(stat+syst)_-0.58^+0.23(model)](10^-4fm³) in agreement with recent evaluations of the Baldin sum rule. Our simultaneous analysis has also provided the first determination of the proton spin polarizabilities, γ_π=-[27.23±2.27(stat+syst)_-2.10^+2.24(model)](10^-4fm⁴), γ₀=-[1.55±0.15(stat+syst)_-0.03^+0.03(model)](10^-4fm⁴), γ₁₃=+[3.94±0.53(stat+syst)_-0.18^+0.20(model)](10^-4fm⁴),and γ₁₄=-[2.20±0.27(stat+syst)_-0.09^+0.05(model)](10^-4fm⁴).The extracted value of the backward spin polarizability, γ_π, is considerably different from other analyses and this has been instrumental in bringing the value of bar α-bar β extracted from high energy data into agreement with low energy experiments.

[en] Neutron cross section covariance library has been under development by BNL-LANL collaborative effort over the last three years. The primary purpose of the library is to provide covariances for the Advanced Fuel Cycle Initiative (AFCI) data adjustment project, which is focusing on the needs of fast advanced burner reactors. The covariances refer to central values given in the 2006 release of the U.S. neutron evaluated library ENDF/B-VII. The preliminary version (AFCI-2.0beta) has been completed in October 2010 and made available to the users for comments. In the final 2.0 release, covariances for a few materials were updated, in particular new LANL evaluations for ^238,240Pu and ²⁴¹Am were adopted. BNL was responsible for covariances for structural materials and fission products, management of the library and coordination of the work, while LANL was in charge of covariances for light nuclei and for actinides.

[en] The cross section covariance library has been under development by BNL-LANL collaborative effort over the last three years. The project builds on two covariance libraries developed earlier, with considerable input from BNL and LANL. In 2006, international effort under WPEC Subgroup 26 produced BOLNA covariance library by putting together data, often preliminary, from various sources for most important materials for nuclear reactor technology. This was followed in 2007 by collaborative effort of four US national laboratories to produce covariances, often of modest quality - hence the name low-fidelity, for virtually complete set of materials included in ENDF/B-VII.0. The present project is focusing on covariances of 4-5 major reaction channels for 110 materials of importance for power reactors. The work started under Global Nuclear Energy Partnership (GNEP) in 2008, which changed to Advanced Fuel Cycle Initiative (AFCI) in 2009. With the 2011 release the name has changed to the Covariance Multigroup Matrix for Advanced Reactor Applications (COMMARA) version 2.0. The primary purpose of the library is to provide covariances for AFCI data adjustment project, which is focusing on the needs of fast advanced burner reactors. Responsibility of BNL was defined as developing covariances for structural materials and fission products, management of the library and coordination of the work; LANL responsibility was defined as covariances for light nuclei and actinides. The COMMARA-2.0 covariance library has been developed by BNL-LANL collaboration for Advanced Fuel Cycle Initiative applications over the period of three years, 2008-2010. It contains covariances for 110 materials relevant to fast reactor R and D. The library is to be used together with the ENDF/B-VII.0 central values of the latest official release of US files of evaluated neutron cross sections. COMMARA-2.0 library contains neutron cross section covariances for 12 light nuclei (coolants and moderators), 78 structural materials and fission products, and 20 actinides. Covariances are given in 33-energy groups, from 10?5 eV to 19.6 MeV, obtained by processing with LANL processing code NJOY using 1/E flux. In addition to these 110 files, the library contains 20 files with nu-bar covariances, 3 files with covariances of prompt fission neutron spectra (238,239,240-Pu), and 2 files with mu-bar covariances (23-Na, 56-Fe). Over the period of three years several working versions of the library have been released and tested by ANL and INL reactor analysts. Useful feedback has been collected allowing gradual improvements of the library. In addition, QA system was developed to check basic properties and features of the whole library, allowing visual inspection of uncertainty and correlations plots, inspection of uncertainties of integral quantities with independent databases, and dispersion of cross sections between major evaluated libraries. The COMMARA-2.0 beta version of the library was released to ANL and INL reactor analysts in October 2010. The final version, described in the present report, was released in March 2011.

[en] The reaction ⁴He(γ→, π⁰)⁴He has been studied with the LEGS tagged, polarized gamma-ray beam. Data are presented at laboratory angles of 31 degrees, 45 degrees, 72.5 degrees, 90 degrees, 110 and 130 degrees for incoming photon energies of 206, 219, 232, 245, 259, 274, 289, 306 and 322 MeV. The unpolarized cross sections are compared with the Δ-hole theoretical model results available in literature. The measured photon beam asymmetry is -1 as expected from conservation of angular momentum and parity

[en] The US Nuclear Data Program is charged with collecting, analyzing and archiving information critical to basic nuclear research and to the development of nuclear technologies. Users of nuclear data require detailed uncertainty information for a variety of reasons. In this paper, we review some of the main aspects of the generation and use of uncertainty information, linking to structure, astrophysics, and reaction data. (paper)