Kaon photoproduction in a multipole approach

Abstract

The recently published experimental data on K+Lambda photoproduction by the SAPHIR, CLAS, and LEPS collaborations are analyzed by means of a multipole approach. For this purpose the background amplitudes are constructed from appropriate Feynman diagrams in a gauge-invariant and crossing-symmetric fashion. The results of our calculation emphasize the lack of mutual consistency between the SAPHIR and CLAS data previously found by several independent research groups, whereas the LEPS data are found to be more consistent with those of CLAS. The use of SAPHIR and CLAS data, individually or simultaneously, leads to quite different resonance parameters which, therefore, could lead to different conclusions on ``missing resonances''. Fitting to the SAPHIR and LEPS data simultaneously indicates that the S_{11}(1650), P_{13}(1720), D_{13}(1700), D_{13}(2080), F_{15}(1680), and F_{15}(2000) resonances are required, while fitting to the combination of CLAS and LEPS data leads alternatively to the P_{13}(1900), D_{13}(2080), D_{15}(1675), F_{15}(1680), and F_{17}(1990) resonances. Although yielding different results in most cases, both SAPHIR and CLAS data indicate that the second peak in the cross sections at W = 1900 MeV originates from the D_{13}(2080) resonance with a mass between 1911 - 1936 MeV. Furthermore, in contrast to the results of currently available models and the Table of Particle Properties, both data sets do not exhibit the need for a P_{11}(1710) resonance. The few data points available for target asymmetry can not be described by the models proposed in the present work.Comment: 33 pages, 14 figure

Gerasimov-Drell-Hearn sum rule and the discrepancy between the new CLAS and SAPHIR data

“…Details of the ingredient of the model can be found in Ref. [4]. A number of free parameters in the background and resonance terms are adjusted by fitting the calculated observables to experimental data.…”

“…[4]. The model consists of the background terms which are constructed from a series of tree-level Feynman diagrams and the resonance terms which are assumed to have the Breit-Wigner form.…”

“…Therefore, Ref. [4] concluded that current data situation does not allow for a precise determination of the resonance parameters or for the search of the "missing resonances".…”

“…It is shown by Refs. [4,5] that the use of SAPHIR and CLAS data, individually or simultaneously, leads to quite different extracted photo-coupling parameters. Therefore, Ref.…”

“…Many recent efforts have been devoted to analyze the consequence of the data discrepancies in the γp → K + Λ process (see e.g., [3,4,6]). It is shown by Refs.…”