B 介子衰變至 τ+τ− 之分析

Abstract

我們在日本筑波KEKB電子-正子對撞機中，使用Belle偵測器中量測的771.581百萬BB介子進行數據分析。我們量測B0 介子衰變至濤子對的事例，而且我們考慮三種濤的衰變模式(τ->e,μ,π)，兩個濤粒子總共六種末態粒子的事例，因為末態粒子有2~4個微中子，所以我們使用強子標籤法來重建事例。為了進一步分辨訊號和背景，我們使用類神經網路演算法來提升訊躁比。我們得到的結果並沒有達到3個標準差之顯著度,在90\%的信心水準下得到的衰變機率上限是1.56 × 10E-3。與之前的量測結果相較，此次量測結果對於量測B介子衰變至τ+τ−有所提升，並提供了於Belle II實驗進行分析的方法。

We perform a search for B0->τ+τ−, based on a data sample of 772 million BB pairs collected at the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e−e+ collider. We consider three τ decay modes ( τ->e,μ,π), which corresponds to six sub-decay final states of B. Since there are 2~4 neutrinos in the final state for signals, we employ the hadronic tagging method to fully reconstruct the accompanying B mesons. The signal and background separation is achieved using the NeuroBaye package with various kinematic variables. No significant signal is found, and we estimate the upper limit of branching fraction at 90% confidence level: B(B0->τ+τ−) < 1.56 × 10E−3. So far the obtained upper limit is the most stringent.