Determining pseudoscalar meson photoproduction amplitudes from complete experiments

Journal Article · Wed Apr 06 04:00:00 EDT 2011 · Journal of Physics. G, Nuclear and Particle Physics

DOI:https://doi.org/10.1088/0954-3899/38/5/053001· OSTI ID:1040499

Sandorfi, A M; Hoblit, S; Sandorfi, A M; Hoblit, S; Kamano, H; Lee, T-S H

A new generation of complete experiments is focused on a high precision extraction of pseudoscalar meson photoproduction amplitudes. Here, we review the development of 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. We examine the different conventions that have been used by different authors, and we present expressions that allow the direct numerical calculation of any pseudoscalar meson photoproduction observables with arbitrary spin projections from the Chew-Goldberger-Low-Nambu amplitudes. We use this numerical tool to clarify apparent sign differences that exist in the literature, in particular with the definitions of six double-polarization observables. We also present analytic expressions that determine the recoil baryon polarization, together with examples of their potential use with quasi-4{pi} detectors to deduce observables. As an illustration of the use of the consistent machinery presented in this review, we carry out a multipole analysis of the {gamma}p {yields} K{sup +}{Lambda} reaction and examine the impact of recently published polarization measurements. When combining data from different experiments, we utilize the Fierz identities to fit a consistent set of scales. In fitting multipoles, we use a combined Monte Carlo sampling of the amplitude space, with gradient minimization, and find a shallow {chi}{sup 2} valley pitted with a very large number of local minima. This results in broad bands of multipole solutions that are experimentally indistinguishable. While these bands have been noticeably narrowed by the inclusion of new polarization measurements, many of the multipoles remain very poorly determined, even in sign, despite the inclusion of data on eight different observables. We have compared multipoles from recent PWA codes with our model-independent solution bands and found that such comparisons provide useful consistency tests which clarify model interpretations. The potential accuracy of amplitudes that could be extracted from measurements of all 16 polarization observables has been studied with mock data using the statistical variations that are expected from ongoing experiments. We conclude that, while a mathematical solution to the problem of determining an amplitude free of ambiguities may require eight observables, as has been pointed out in the literature, experiments with realistically achievable uncertainties will require a significantly larger number.

• Research Organization: Brookhaven National Laboratory (BNL) National Nuclear Data Center
• Sponsoring Organization: USDOE NE OFFICE OF NUCLEAR ENERGY (NE)
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 1040499
• Report Number(s): BNL--96267-2011-JA; KB0301041
• Journal Information: Journal of Physics. G, Nuclear and Particle Physics, Journal Name: Journal of Physics. G, Nuclear and Particle Physics Journal Issue: 5 Vol. 38; ISSN 0954-3899; ISSN JPGPED
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ACCURACY
AMPLITUDES
BARYONS
CROSS SECTIONS
MACHINERY
MATHEMATICAL SOLUTIONS
MINIMIZATION
MULTIPOLES
PHOTOPRODUCTION
POLARIZATION
PSEUDOSCALAR MESONS
SAMPLING
SPIN
TARGETS
VECTORS
national nuclear data center