尋找B介子的二體輕子及二體重子衰變

本篇論文是以三個主題作為舖陳。第一個主題所介紹的是硬體研發，此研發乃是Belle偵測器內部的矽頂點偵測器升級相關硬體之一：時序模組。第二個和第三個主題都是以Belle偵測器所蒐集的數據資料所做的分析：尋找B介子的二體輕子衰變和二體重子衰變。這三個主題的安排，是依照完成的先後順序進行著墨。台大高能團隊所負責研發的時序模組，可以提供正確的時序訊號給矽頂點偵測器的讀出系統。除了提供正確的時序訊號之外，並同時同步化了時序在矽感應器前端和後端的讀出。至於測試方面，我們藉由前端的讀出系統，讓時序模組提供以較慢速度的時序訊號來檢查矽感應器的讀出晶片以及進行線上即時監控。時序模組的研發成果按時的送到Belle實驗的所在地─日本筑波的高能研究機構 (KEK)，並且成功的發揮運作至今。至於數據分析方面，我首先嘗試的是超越標準模型的新物理探討：二體輕子衰變。再來是嘗試標準模型規範下可能出現的二體重子衰變。數據資料的來源是Belle偵測器在加速器內的電子-正電子束對撞中心點所收集的事件。我使用了78 fb-1的數據於二體輕子衰變的研究，而以140 fb-1做二體重子衰變的研究。研究結果顯示：B介子的二體輕子衰變以及二體重子衰變發生的可能性極低。以目前的數據量，尚且看不到此種衰變。所以，我們只能量測到這種衰變的衰變率上限，此上限是以統計學上到達百分之九十的信心程度而言。所得到的二體輕子的衰變率上限為：B(B0 → e+e-) < 1.9 x 10-7，B(B0 → m+m-) < 1.6 x 10-7，B(B0 → em) < 1.7 x 10-7。依據Pati-Salam的理論模型所提出的輕夸克 (LeptoQuark) 與B0 → em 的衰變關係式，我們以上述得到的B(B0 → em)衰變率上限，為此種輕夸克的質量計算出其統計學上百分之九十信心程度的下限： MLQ > 46 TeV/c2。同理，以統計學上到達百分之九十的信心程度所得到的二體重子的衰變率上限為：B(B0 →pp~) < 5.0 x 10-7，B(B0 →Lambda Lambda~) < 7.9 x 10-7，B(B+ → p Lambda~) < 4.6 x 10-7。

關鍵字

Belle 實驗；日本筑波的高能實驗機構；矽頂點偵測器升級相關硬體； B介子；二體輕子衰變；二體重子衰變；時序模組

並列摘要

Three major topics are presented in this thesis. The first one is the back-end electronics design for the Silicon Vertex Detector (SVD2) at Belle - the Trigger Timing Modules (TTM2). The other two are the physics analyses on the search for two-body leptonic and baryonic $B$ decays at Belle. The order of the arrangement is chronological. The NTUHEPfootnote{National Taiwan University High Energy Experimental Physics} group was responsible to design the TTM2, which provides correct timing information for the SVD2 readout electronics. The TTM2 not only provides correct timing signals but also synchronizes the SVD2 front-end and back-end readout electronics. Besides, the TTM2 allows slow control and monitors the data between the readout chips of the silicon sensor and an on-line computer via the front-end readout electronics. The delivery of the TTM2 to KEK was on time and it is working properly. The subject of my first data analysis was the search for new physics beyond the Standard Model in two-body leptonic decays. This was followed by the try to discover various two-body baryonic decays in the increasing data statistics. The data events are collected by the Belle detector at KEKB. For the leptonic and baryonic decays, I use 78 fb$^{-1}$ and 140 fb$^{-1}$ of data, respectively. No candidates are found for the leptonic modes; no significant signals are observed for baryonic modes. Wefootnote{Belle Collaboration} report the 90\% confidence level upper limits for the leptonic modes: $mathcal {B} (B^0 o e^+ e^-) < 1.9 imes 10^{-7}$, $mathcal {B} (B^0 o mu^+ mu^-) < 1.6 imes 10^{-7}$, and $mathcal {B} (B^0 o e^{pm} mu^{mp}) < 1.7 imes 10^{-7}$. A limit on the Pati-Salam leptoquark mass $M_{LQ} >$ 46 TeV/$c^2$ is obtained at the 90\% confidence level, based on the $B^0 o e^{pm} mu^{mp}$ limit. For the baryonic modes, the 90\% confidence level upper limits are estimated to be $mathcal {B} (B^0 o p ar{p}) < 5.0 imes 10^{-7}$, $mathcal {B} (B^0 o Lambda ar{Lambda}) < 7.9 imes 10^{-7}$, and $mathcal {B} (B^+ o p ar{Lambda}) < 4.6 imes 10^{-7}$.

並列關鍵字

electronics design for the Silicon Vertex Detector at Belle experiment ； KEK ； trigger timing module ； B meson ； two-body leptonic decay ； two-body baryonic decay

參考文獻

\bibitem{KEKB} S.~Kurokawa and E.~Kikutani, Nucl. Instr. and Meth. A {\bf 499},

1 (2003), and other papers included in this Volume.

\bibitem{efc} M.Z. Wang {\it et al.}, Nucl. Instr. and Meth. A {\bf 455}, 319 (2000).

\bibitem{GDL} Y. Ushiroda {\it et al.}, Nucl. Instr. and Meth. A {\bf 438}, 460 (1999).

\bibitem{DAQ} M. Nakao {\it et al.}, IEEE Trans. Nucl. Sci. {\bf 47}, 56 (2000).

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尋找B介子的二體輕子及二體重子衰變

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