Measurement of Λ Polarization in the π p → K0 Λ Reaction at pπ=1.33 GeV/c toward a New Λ p Scattering Experiment

초록

Understanding the spectrum and dynamics of excited nucleon states (N* resonances) remains a central challenge in hadron physics, as these resonances emerge in intermediate states of pi N and gamma N interactions. The dynamical coupled-channel models addressing this problem rely critically on experimental inputs for partial wave analyses. However, polarization observables of hyperons, which serve as sensitive probes of reaction mechanisms, have so far been limited in precision. To address this, we aim to provide high-precision measurements of the polarization of the Lambda hyperon produced in the pi(-)p -> K0 Lambda reaction. The data were obtained with the Japan Proton Accelerator Research Complex (J-PARC) E40 experiment at the K1.8 beamline of the J-PARC Hadron Experimental Facility. The polarization of the Lambda was precisely measured in the angular range 0.6 < cos theta(K0) (CM) < 1.0 with a fine bin width of 0.6 < cos theta(K0) (CM) < 1.0. The observed average polarization in the region 0.6 < cos theta K0 CM < 1.0 was 0.932 +/- 0.058(stat.) +/- 0.028(syst.). These results provide essential input for partial wave analyses of dynamical coupled-channel models, contributing to a deeper understanding of N* resonance dynamics. Furthermore, the strong Lambda polarization observed indicates the feasibility of generating a highly polarized Lambda beam, opening prospects for future Lambda p scattering experiments such as J-PARC E86.