Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland.
Phys Rev Lett. 2011 May 13;106(19):191801. doi: 10.1103/PhysRevLett.106.191801. Epub 2011 May 12.
We present a search for a new particle T' decaying to top quark via T' → t + X, where X is an invisible particle. In a data sample with 4.8 fb(-1) of integrated luminosity collected by the CDF II detector at Fermilab in pp collisions with √s = 1.96 TeV, we search for pair production of T' in the lepton + jets channel, pp → tt + X + X → ℓνbqq'b + X + X. We interpret our results primarily in terms of a model where T' are exotic fourth generation quarks and X are dark matter particles. Current direct and indirect bounds on such exotic quarks restrict their masses to be between 300 and 600 GeV/c2, the dark matter particle mass being anywhere below m(T'). The data are consistent with standard model expectations, and we set 95% confidence level limits on the generic production of T'T' → tt + X + X. For the dark matter model we exclude T' at 95% confidence level up to m(T') = 360 GeV/c2 for m(X) ≤ 100 GeV/c2.
我们提出了一种搜索新粒子 T' 的方法，该粒子通过 T' → t + X 衰变，其中 X 是一个不可见的粒子。在费米实验室的 CDF II 探测器在 pp 碰撞中收集的 4.8 fb(-1)积分亮度的数据样本中，我们在 lepton + jets 通道中搜索 T' 的对产生，pp → tt + X + X → ℓνbqq'b + X + X。我们主要根据一种模型来解释我们的结果，在该模型中，T' 是奇异的第四代夸克，X 是暗物质粒子。目前对这种奇异夸克的直接和间接限制将它们的质量限制在 300 到 600 GeV/c2 之间，暗物质粒子的质量在 m(T') 以下的任何地方。数据与标准模型的预期一致，我们对一般的 T'T' → tt + X + X 产生设定了 95%置信水平的限制。对于暗物质模型，我们在 95%置信水平下排除了 T'，直到 m(T') = 360 GeV/c2，对于 m(X) ≤ 100 GeV/c2。
