Energy and System Size Dependence of Xi− and Xi+ Production in Relativistic Heavy-Ion Collisions at the CERN SPS

Table of Contents

1. Introduction

1.1. Hadronic Matter

1.1.1. Quark Combinations

1.1.2. Color Charge

1.2. The Strong Interaction: Confinement

1.2.1. Chiral Symmetry Restoration

1.3. The Phase Diagram of Strongly Interacting Matter

1.4. Relativistic Heavy Ion Collisions

1.5. Strangeness

1.5.1. Strangeness Production in a Hadronic Gas

1.5.2. Strangeness Production in a Quark Gluon Plasma

2. The NA49 Experiment at CERN SPS

2.1. The NA49 Detector Layout

2.2. Time Projection Chambers

2.2.1. The NA49 TPCs

2.3. Event Reconstruction

2.3.1. V0 Reconstruction

2.3.2. V0 Finding

2.3.3. V0 Fitting

2.3.4. Multi-Strange Hyperon Reconstruction

2.3.5. Ξ Finding

3. Data Analysis

3.1. Data sets

3.2. Event Cuts

3.2.1. Central Pb+Pb

3.2.2. Minimum Bias Pb+Pb

3.2.3. Semi-Central Si+Si

3.3. Analysis Cuts

3.3.1. Cuts on the Ξ Candidate

3.3.2. Cuts on the Daughter π of the Ξ Candidate

3.3.3. Cuts on the Daughter Λ Candidate

3.4. Invariant mass method

3.5. Correction

3.5.1. Geometrical Acceptance

3.5.2. Reconstruction Efficiency

3.5.3. Centrality Bin Size Effect

3.5.4. Influence of δ Electrons

4. Extraction of Spectra, Yields and Systematic Error

4.1. Transverse Momentum and Transverse Mass Spectra

4.1.1. Extrapolation of the Transverse Momentum Spectra

4.2. Rapidity Spectra and 4π Yields

4.3. Stability Checks of the Results and the Systematic Error

4.4. Lifetime

4.5. Comparision with another Ξ Analysis at 158 AGeV

5. Discussion

5.1. Comparison with Other Experiments

5.2. Energy Dependence

5.2.1. Inverse Slope Parameter and Mean Transverse Mass of the Ξ Hyperon

5.2.2. Strange Hadron Yield Enhancement

5.2.3. Excitation Function of Ξ production

5.2.4. Antibaryon/Baryon Ratio

5.3. Theoretical Models

5.3.1. Spectator-Participant Model

5.3.2. RQMD v2.3

5.3.3. UrQMD v1.3

5.3.4. Statistical Hadron Gas Models

5.3.5. Comparison to Models

6. Summary and Conclusion

Objectives and Topics

The primary objective of this dissertation is the experimental analysis of the energy and system-size dependence of Ξ-hyperon production in heavy-ion collisions at the CERN Super Proton Synchrotron (SPS). The work investigates whether the production rates of these strange particles provide evidence for the formation of a Quark Gluon Plasma (QGP) and examines how these findings compare to predictions from statistical and microscopic theoretical models.

• Investigation of the energy dependence of Ξ- production in central and minimum-bias Pb+Pb collisions.
• Study of the impact of system size on hyperon production, including data from Si+Si collisions.
• Evaluation of strangeness enhancement as a diagnostic signature for the deconfinement phase transition.
• Comprehensive comparison of experimental results with established theoretical frameworks such as UrQMD, RQMD, and Statistical Hadron Gas models.

Excerpt from the Book

Summary of Chapters

1. Introduction: Summarizes the fundamental concepts of hadronic matter, the role of QCD, and the motivation for studying strangeness in relativistic heavy-ion collisions as a signature for the QGP.

2. The NA49 Experiment at CERN SPS: Describes the experimental apparatus, including the Time Projection Chambers, and the data reconstruction procedures used to identify strange hadrons.

3. Data Analysis: Details the systematic data selection process, including event and track cuts, the invariant mass method for particle identification, and the necessary efficiency corrections.

4. Extraction of Spectra, Yields and Systematic Error: Explains the methodologies for calculating transverse momentum and rapidity spectra, as well as the estimation of systematic uncertainties in the measurement.

5. Discussion: Compares the experimental results with other experiments and theoretical models, focusing on energy and system-size dependencies and the interpretation of strangeness enhancement.

6. Summary and Conclusion: Consolidates the findings regarding Ξ-production, re-evaluates the validity of strangeness enhancement as a QGP indicator, and discusses the implications for phase transition physics.

Keywords

Quark Gluon Plasma, QGP, Relativistic Heavy-Ion Collisions, CERN SPS, NA49 Experiment, Strangeness Production, Ξ-Hyperons, Quantum Chromodynamics, QCD, Confinement, Deconfinement, Hadronic Matter, Transverse Momentum Spectra, Rapidity Spectra, Statistical Models

Frequently Asked Questions

What is the core subject of this thesis?

This thesis focuses on the production of strange baryons, specifically Ξ- and Ξ-bar hyperons, in relativistic heavy-ion collisions at the CERN SPS accelerator.

What are the primary research themes?

The work examines the energy and system-size dependence of strangeness production, the role of hadronic versus deconfined (QGP) phases, and the validity of strangeness enhancement as a signal for the QGP.

What is the main objective?

The objective is to analyze experimental data from the NA49 detector to test if the production of multi-strange hyperons provides consistent evidence for the deconfinement phase transition and to compare these results with existing theoretical predictions.

Which scientific methods are employed?

The analysis utilizes the "bin-by-bin" correction method to account for detector acceptance and efficiency, applies geometric and kinematic analysis cuts, and uses invariant mass reconstruction to extract yields.

What does the main body cover?

It covers the detector setup, the data reconstruction chain, the specific cut criteria for Ξ- identification, the extraction of spectra and systematic errors, and a discussion comparing the data with models like UrQMD and Statistical Hadron Gas models.

Which keywords best characterize this work?

Key terms include QGP, NA49, Ξ-Hyperons, strangeness enhancement, heavy-ion collisions, and QCD.

Why are Ξ-hyperons significant for this research?

Ξ-hyperons are multi-strange particles; their production is expected to be significantly higher in a deconfined QGP compared to a standard hadronic gas, making them effective probes for the phase of the system.

What is the conclusion regarding the NA57 comparison?

The thesis identifies a discrepancy between its results and those reported by the NA57 collaboration, which remains an open issue in the field of high-energy physics.