Study of ambiguities in π−p → ΛK0 scattering amplitudes

Abstract

Abstract. Amplitudes for the reaction π − p → ΛK 0 are reconstructed from data on the differential cross section dσ/dΩ, the recoil polarization P , and on the spin rotation parameter β. At low energies, no data on β exist, resulting in ambiguities. An approximation using S and P waves leads only to a fair description of the data on dσ/dΩ and P ; in this case, there are two sets of amplitudes. Including D waves, the data on dσ/dΩ and P are well reproduced by the fit but now, there are several distinct solutions which describe the data with identical precision. In the range where the spin rotation parameter β was measured, a full and unambiguous reconstruction of the partial wave amplitudes is possible. The energy-independent (single-energy) amplitudes are compared to the energy dependent amplitudes which resulted from a coupled channel fit (BnGa2011-02) to a large data set including both pion and photo-induced reactions. Significant deviations are observed. Consistency between energy dependent and energy independent solutions is obtained by choosing the energy independent solution which is closest to the energy dependent solution. In a second step, the known energy dependent solution for low (or high) partial waves is imposed and only the high (or low) partial waves are fitted leading to smaller uncertainties.

Pole positions and residues from pion photoproduction using the Laurent-Pietarinen expansion method

“…• SAID ED 0.0049 (19) 124 (20) • 0.0433(17) −12 (3) • 0.014 (5) 130 (20) • 0.123(4) −6(3) (2) 20 (2) • 0.132 (4) 27 (3) • SAID ED 0.0141(7) −14 (2) • 0.0117(12) −1(3)…”

“…Apart from its ease of use, it provides a tool for the extraction and comparison of pole properties from different analyses. There have been several recent studies of model-dependence in single-energy photoproduction amplitude reconstruction [18] (both helicity and multipole), with extensions to other reactions as well [19]. The simplicity of the our expansion method enables us to self-consistently analyze and compare results from different approaches, as described below.…”

Partial wave analysis

“…In a first step, we analyzed the reaction π − p → ΛK 0 [169] and determined low-lying multipoles. Ambiguities and large fluctuations showed up.…”

Combined analysis of theπ−p→K0Λ,ηnreactions in a chiral quark model

“…In theory, various theoretical approaches have been applied to analyze the π − p → K 0 Λ and/or ηn reactions, such as the chiral unitary model [24], K-matrix methods [25][26][27][28][29][30][31][32][33][34][35], dynamical coupled-channel models [7,[36][37][38][39][40][41], the BnGa approach [42], chiral quark model [43,44], and other effective approachs [45][46][47], etc. However, the analyses from different models claim a different resonance content in the reactions [6].…”