在7TeV質心能量的質子對撞機實驗中尋找帶2/3電荷的類向量頂夸克透過頂夸克和Z波色子的事件

Abstract

藉由在大強子對撞機上的緊湊渺子線圈偵測器，我們採用質心能量為7 TeV的質子對撞事件來尋找帶2/3電荷成對出現的類向量頂夸克（Ｔ）。透過Ｔ夸克的味改變中性流衰變至頂夸克以及Ｚ波色子，兩個來自Ｚ波色子的輕子以及另一個帶電、獨自的輕子被當作觀測訊號事件的考量。使用1.14 /fb 的統一光度，觀測到的事件數和標準模型背景預測是一致的。假設100%的Ｔ夸克衰變為頂夸克以及Ｚ波色子，在95%的信心水準下，質量小於475GeV/c2的Ｔ夸克是不存在的。

We present a search for pair-produced vector-like charge 2/3 quarks, T, in pp collisions at a center-of-mass energy of 7 TeV performed by the CMS experiment at the LHC. Events consistent with the flavor changing neutral current decay of a T quark to a top quark and a Z boson are selected by requiring two leptons from the Z decay as well as an additional isolated, charged lepton. With an integrated luminosity of 1.14 /fb, the observed events are found to be consistent with the standard model background prediction. Assuming a branching fraction of 100% for the decay T -> tZ, a T quark with mass less than 475 GeV/c2 is excluded at a 95% confidence level.