Measurement of the beam Λ polarization for the next Λp scattering experiment at J-PARC

• 🐬AUTHOR: Tamao SAKAO (坂尾　珠和)
• 📄DOCUMENT TYPE: Dissertation
• 🏫AFFILIATION: Dept. of Physics, Facl. of Science, Tohoku University (Sendai, Japan).
• 📧E-MAIL: [email protected]
• ⚠️CAUTION: please read the full pdf file from HERE. If you want to reuse codes here, please let me know.

Abstract

The study of baryon-baryon interactions is essential to understand the fundamental forces in particle physics. This thesis focuses on the interactions within the SU(3) flavor symmetry framework, involving different types of baryons such as protons, neutrons, and hyperons. Experimental data, primarily from the J-PARC E40 experiment, is analyzed to derive $\Lambda$ polarization in the $\pi^{-}p\to K^{0}\Lambda$ reaction. Also, the $\Lambda p$ scattering identification method was established using the same data.

Chapter1: Introduction

The nuclear force is significant in binding protons and neutrons in atomic nuclei. The nuclear force is described as repulsive at short range and attractive at long range, crucial for stabilizing nuclei. However, the origin of its repulsive core is still unreveal. It discusses the meson exchange model explaining nuclear force and the importance of understanding interactions between baryons, especially those containing different quark flavors, under the SU(3) flavor symmetry. The chapter also outlines the significance of studying the Λp scattering experiment, aiming to contribute to the understanding of nuclear force and many-body systems involving hyperons like hypernuclei and neutron stars​​.

Chapter2: Experiment

This chapter describes the experimental setup and execution of J-PARC E40 at the K1.8 beamline in the J-PARC Hadron Experimental Facility. It covers the production and measurement of $\Sigma^{\pm}p$ elastic scatterings and the $\Sigma^{-}p\to\Lambda n$ inelastic scattering using high-intensity pion beams. Detailed information is provided on the $\Sigma^{+}$ and $\Sigma^{−}$ beam production, the use of a liquid hydrogen target, and the accumulation of significant data for various scattering events. The chapter emphasizes the analysis of $\pi^{-}p\to K^{0}\Lambda$ reaction data accumulated during the $\Sigma^{-}$ run data​​.

Chapter3: Flow of Analysis and Simulation

This chapter describes the flow of analyses and Monte Carlo-base Geant4 simulations used in this research.

Chapter 4: Beam $\Lambda$ Identification

This chapter explains the process of identifying $\Lambda$ particles produced from the $\pi^{-}p\to K^{0}\Lambda$ reaction. It details the techniques and criteria used to distinguish $\Lambda$ particles from other reaction products and background events. The chapter emphasizes the importance of accurate identification for subsequent analyses and measurements​​.

Chapter 5: Beam $\Lambda$ Polarization Measurement

This chapter describes the detailed process and results of measuring $\Lambda$ polarization. It discusses the development of the polarization analysis method, the improvement of measurement accuracy, and the verification of previous results. The chapter includes numerical values and distributions relevant to the polarization measurement, highlighting the significance of these measurements in understanding the $\Lambda p$ interaction​​.

Chapter 6: $\Lambda p$ Scattering Identification

This chapter focuses on the identification of $\Lambda p$ scattering events. It describes the methods developed to achieve a high signal-to-noise ratio in identifying $\Lambda p$ scatterings. The chapter includes analysis of background events such as $pp$ elastic scattering and $\Lambda\to p\pi^{-}$ decay, and the optimization of event selection to minimize these backgrounds. The results contribute to the understanding of $\Lambda p$ interactions and the theoretical models of nuclear force​​.

Chapter 7: Summary

The final chapter summarizes the results of the J-PARC E40 experiment and discusses the implications for the upcoming J-PARC E86 experiment. It emphasizes the importance of measuring spin observables and differential cross-sections in the $\Lambda p$ channel to place strong constraints on theoretical models. The chapter outlines the future research directions and the significance of building realistic $\Lambda N$ interactions for studying many-body systems containing $\Lambda$ hyperons​​.