在7和8TeV質心能量質子對撞中藉底夸克加Z波色子事件尋找成對產生的類向量夸克

Abstract

這是個尋找成對產生類向量夸克B’ 的研究。所用的實驗數據是在大強子對撞機(LHC) 運轉時，分別在2011 年以7 TeV 和2012 年以8 TeV 質心能量的質子對撞並由緊湊渺子線圈(CMS) 偵測器取得，累積的數據量達4.9 fb−1 (2011)，19.6 fb−1 (2012)。由底夸克標籤的粒子噴流和從電子對或渺子對重建的Z 波色子所組合的不變質量，其符合標準模型的預測。在2011 年的數據下，假設B’ 衰變為一個底夸克和一個Z 波色子的分支所占比率為100% 時，則有95% 的信心水準下預期質量下限為510 GeV/c2，而觀測所得下限為550 GeV/c2。2012 年更新的預期下限為680 GeV/c2 而觀測所得為700 GeV/c2。

A search is presented for the pair production of a vector-like quark, B’. Data corresponding to integrated luminosity of 4.9 fb−1 p from pp collisions at √s = 7 TeV in 2011 and 19.6 fb−1 at 8 TeV in 2012 collected with the CMS detector at the LHC were used. The invariant mass spectrum of b-tagged jets and Z boson candidates, with the latter identified through e+e− or μ+μ− decays, is examined for an excess of events and found to be consistent with the standard model expectations. The expected 95% confidence level lower limit on the mass of the B’ quark with the assumption a 100% branching ratio fraction into a bottom quark and a Z boson is 510 GeV/c2, while the observed lower limit is 550 GeV/c2 in 2011; For the updates in 2012, the expected limit is 680 GeV/c2 and observed lower limit is 700 GeV/c2.