A Limit on the Branching Ratio of the Flavor-Changing Top Quark Decay t → Zc
A Limit on the Branching Ratio of the Flavor-Changing Top Quark Decay t → Zc
复制标题
变味顶夸克衰变支化率的极限 t → Zc
DOI：
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发表时间：
2008
期刊：
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通讯作者：
H. Frisch
中科院分区：
文献类型：
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作者：
H. Frisch
我们测量的上限为8.3%（95% C.L.）使用1.52 fb−1的数据，对100%纵向极化Z玻色子的味道变化顶夸克衰变t → Zc的分支比进行了研究。我们参数化的上限作为Z玻色子的螺旋度的函数，以涵盖可能的衰变结构的全部范围。分析是基于两个过程的比较：pp → tt → WbWb → lνbjjb和pp → tt → ZcWb → l+l−cjjb。这两种衰变模式的共同使用允许消除主要的系统不确定性的接受，效率和光度。我们验证的MC模型的接受和效率轻子识别多年的数据集的精确测量的比率的包容性生产的Wand Z-玻色子。为了提高鉴别力，我们计算了每个事件的顶质量与两个轻子和四个喷流假设它是一个TT-事件与一个顶夸克衰变到Zc。顶部质量的计算由装配工逐个事件进行。Br（t → Zc）的上限由l+ l-cjjb顶质量分布的二维可能性和“l +6 ET +4喷流”事件的数量估计。目前的研究结果还受到统计数据的限制。
We measure an upper limit of 8.3% (95% C.L.) on the branching ratio of the flavor-changing top quark decay t → Zc for 100% longitudinally polarized Z-bosons using 1.52 fb−1 of data. We parametrize the upper limit as a function of Z-boson’s helicity to cover the full range of possible decay structures. The analysis is based on the comparison of two processes: pp̄ → tt̄ → WbWb → lνbjjb and pp̄ → tt̄ → ZcWb → l+l−cjjb. The use of these two decay modes together allows cancellation of major systematic uncertainties of acceptance, efficiency, and luminosity. We validate the MC modeling of acceptance and efficiency for lepton identification over the multi-year dataset by a precision measurement of the ratio of the inclusive production of Wand Z-bosons. To improve the discrimination, we calculate the top mass for each event with two leptons and four jets assuming it is a tt̄ event with one of the top quarks decaying to Zc. The calculation of the top mass is performed with a fitter on an event-by-event basis. The upper limit on the Br(t → Zc) is estimated from a 2-dimensional likelihood of the l+l−cjjb top mass distribution and the number of “l + 6ET + 4jets” events. The results are limited by statistics at present.