測量 Belle II 中 B0 → K0 π0 之衰變率及宇稱不對稱性與首次 Belle 實驗雙粒子關聯性研究

Measurement of Branching Fraction and Direct CP Asymmetry in B0 → K0 π0 Decay at Belle II and First Study of Two-Particle Correlations at Belle

陳昱蓁(Yu-Chen Chen)

指導教授 ： 張寶棣

國立臺灣大學/理學院/物理學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202100981

摘要

本論文紀錄 Belle 與 Belle II 實驗中兩分析。首先為 B0 → K0 π0 之衰變率及宇稱不對稱性(CP)的測量。透過非訊號端之另一 B 介子衰變(Btag)識別衰變的風味，繼而使用時間積分方法來測量直接 CP 不對稱參數。本測量使用 62.8 fb-1 總體光度的早期 Belle II 資料，得出
B(B0 → K0 π0) = [8.5_{-1.6}^{+1.7} ± 1.2] × 10^{-6} 與
AK0π0 = -0.40_{-0.44}^{+0.46} ± 0.04,
其中誤差項第一者為統計誤差，次者為系統誤差。

第二個主題為首次使用非共振(√s = 10.52 GeV)與共振(√s = 10.58 GeV)Belle數據之雙粒子關聯性測量，分別對應 89.5 fb-1及 332.2 fb-1 的積分亮度。本分析其中一個核心目標為與強子對撞實驗進行尋找長距(大贋快度 ∆η)、近處(小方位角 Δɸ)的"脊訊號"的比較，其中脊訊號為廣泛在質子質子、質子原子和原子原子對撞實驗中觀測到的現象，但尚未獲得完全了解。本結果與使用 ALEPH 公開資料的測量一致，並未觀察到顯著的脊訊號。此研究也與蒙地卡羅事件生成器做比較，進而提供對於現象學的碎片化模型的看法。

關鍵字

Belle 與 Belle II 實驗 ； B 介子 ； 稀有 B 衰變 ； 宇稱不對稱性 ； 量子色動力學 ； 夸克-膠子電漿

並列摘要

This thesis documents two studies of Belle and Belle II experiments. The first is the branching fraction and the direct CP asymmetry measurements for the B0 → K0 π0 decay. The flavor content of the pair-produced neutral B partner (Btag) is used to identify the flavor information of the decay, succeeded with the time-integrated method to determine the direct CP asymmetry parameter. The measurement is obtained with the early-stage Belle II dataset of 62.8 fb-1 integrated luminosity, resulting
B(B0 → K0 π0) = [8.5_{-1.6}^{+1.7} ± 1.2] × 10^{-6} and
AK0π0 = -0.40_{-0.44}^{+0.46} ± 0.04,
where the first uncertainties are statistical and the second are systematic.

The second topic is the first two-particle correlation function measurement with off-resonance (√s = 10.52 GeV) and on-resonance (√s = 10.58 GeV) Belle data, corresponding to 31.5 fb-1 and 332.2 fb-1, respectively. One of the essential goals of this analysis is to compare with hadronic collision experiments on searching for the long-range (large pseudorapidity difference Δη), near-side (small azimuthal angle difference Δɸ) "ridge signal", which is a phenomenon widely observed but not yet well understood in pp, pA and AA collisions. The results are consistent with the measurement with ALEPH open data, and no significant excess of ridge signal is observed. The analysis is also compared with expectations from Monte Carlo event generators, offering insights to phenomenological fragmentation models.

並列關鍵字

Belle and Belle II ； B meson ； rare B decay ； CP asymmetry ； Quantum chromodynamics ； Quark-gluon plasma

參考文獻

A. Abashian et al., The Belle Detector, Nucl. Instrum. Meth. A 479, 117 (2002).

N.Braun, A.Glazov, F.Metzer, and E.Paoloni, Study of the collision point properties (2018).

T. Abe, Belle II Technical Design Report, KEK-REPORT-2010-1 (2010).

Y. Funakoshi, Operational experience with crab cavities at KEKB (2014).

A. J. Bevan et al., The Physics of the B Factories, Eur. Phys. J. C 74, 3026 (2014).