Measurement of $\Lambda$ Polarization in the $\pi^{-}p \to K^{0} \Lambda$ Reaction at $p_{\pi^{-}}=1.33$ GeV/$c$ toward a New $\Lambda p$ Scattering Experiment

TL;DR

This paper reports high-precision measurements of $\Lambda$ hyperon polarization in the $\pi^- ext{p} o ext{K}^0 ext{Lambda}$ reaction at 1.33 GeV/c, providing valuable data for partial wave analysis and future $ ext{Lambda p}$ scattering experiments.

Contribution

It provides the first high-precision polarization data of $\Lambda$ hyperons in this reaction, supporting partial wave analysis and demonstrating the feasibility of polarized $\Lambda$ beams.

Findings

Average polarization of 0.932 with statistical and systematic uncertainties.

Data covers angular range $0.6< ext{cos} heta^{CM}_{K^0}<0.85$.

Supports future $ ext{Lambda p}$ scattering experiments.

Abstract

This paper presents high-precision experimental data of the polarization of the $\Lambda$ hyperon in the $\pi^{-}p \to K^{0} \Lambda$ reaction, measured in the angular range $0.6<\cos \theta ^{CM}_{K0}<1.0$ with a fine bin width of $d\cos \theta ^{CM}_{K0}=0.05$. The data were obtained from the J-PARC E40 experiment at the K1.8 beamline in the J-PARC Hadron Experimental Facility. The observed average polarization of $\Lambda$ in the range $0.60<\cos \theta ^{CM}_{K0}<0.85$ was $0.932 \pm 0.058 \,(\text{stat}) \pm 0.028 \,(\text{syst})$, demonstrating the successful extraction of precise polarization observables. This result provides essential experimental input for partial wave analysis (PWA) of dynamical coupled-channel (DCC) models, which aim to uncover the underlying mechanisms of $N^{*}$ resonances that emerge in intermediate states of $\pi N$ and $\gamma N$ interactions. Besides, it indicates the feasibility of a strongly polarized $\Lambda$ beam suitable for future $\Lambda p$ scattering experiments (e.g., J-PARC E86).