在Belle II實驗中對B+介子衰變至µ+ν之敏感度分析

Abstract

本研究旨在預測「假設標準模型對於B+→µ+ν之分支分數預測正確，則在不同 Belle II資料量下，B+→µ+ν之統計顯著性分別為何」。本研究使用蒙地卡羅方法產生大量資料樣本以模擬e+e−在SuperKEKB加速器中以10.58 GeV質心能量對撞所產生之各種物理事件。這些物理事件包含了e+e−→qq、e+e−→τ+τ−以及e+e−→Υ(4S)→ B0B0bar/B+B−之過程。我們也模擬了Belle II探測器對這些物理事件之反應。本研究使用多變量分析以區隔B+→µ+ν事件及背景事件。我們為不同物理過程建立機率密度函數並產生艾西莫夫資料，並使用其剖面概似函數預測不同Belle II資料量下B+→µ+ν之統計顯著性。根據預測，我們需要多於7 ab−1之資料量以超越5σ之顯著性以宣稱發現B+→µ+ν衰變。

In this study, we intend to estimate the statistical significance of B+→µ+ν when various amounts of Belle II data are available in the future, assuming that the Standard Model estimation of the branching fraction of B+→µ+ν is correct. The Monte-Carlo method is applied to generate a large amount of data samples to simulate the physics events produced by e+e− collision on the center­-of-­mass energy of 10.58 GeV in the SuperKEKB accelerator. These physics events include the e+e−→qq, the e+e−→τ+τ−, and the e+e−→Υ(4S)→B0B0bar/B+B− processes. The Belle II detector responses to these physics events are also simulated. In this study, we use multivariate analysis to distinguish the B+→μ+ν events from the background events. We establish probability density functions for different physics processes and generate Asimov data sets. We then use the profile likelihood function of the Asimov data sets to estimate the statistical significance of B+→μ+ν when different amounts of Belle II data are available. According to the estimation, we will need to collect more than 7ab−1 of data in order to surpass the significance of 5σ in order to claim the discovery of B+→μ+ν