Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland.
Phys Rev Lett. 2011 Apr 8;106(14):141803. doi: 10.1103/PhysRevLett.106.141803. Epub 2011 Apr 6.
We report the most sensitive direct search for pair production of fourth-generation bottomlike chiral quarks (b') each decaying promptly to tW. We search for an excess of events with an electron or muon, at least five jets (one identified as due to a b or c quark), and an imbalance of transverse momentum by using data from pp collisions collected by the CDF II detector at Fermilab with an integrated luminosity of 4.8 fb(-1). We observe events consistent with background expectation, calculate upper limits on the b' pair-production cross section (σ(bb')) ≲30 fb for m(b') > 375 GeV/c2), and exclude m(b') < 372 GeV/c2 at 95% confidence level assuming a 100% branching ratio of b' to tW.
我们报告了对第四代类底夸克（b'）对产生的最灵敏直接搜索，每个 b' 都迅速衰变为 tW。我们使用费米实验室的 CDF II 探测器在 pp 碰撞中收集的数据，在至少有一个电子或缪子、五个喷注（一个被识别为来自 b 或 c 夸克）和横向动量不平衡的情况下，搜索事件过量，这些数据的积分亮度为 4.8 fb^-1。我们观察到与背景预期一致的事件，计算出 m(b')>375 GeV/c^2 时 b' 对产生的截面（σ（bb'））≲30 fb^-1 的上界，并在假设 b' 到 tW 的分支比为 100%的情况下，在 95%置信水平下排除 m(b')<372 GeV/c^2。
