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arXiv 1104.3874hep-phhep-ex
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在强子对撞机上探测第四代夸克

Detecting Fourth Generation Quarks at Hadron Colliders

David Atwood, Sudhir Kumar Gupta, Amarjit Soni

备注：
26 pages; 15 Figures; In version 2 we have added some references and corrected some typos; Version 3 we have made minor change to some figure captions
发表信息：
JHEP 1206 (2012) 105
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摘要：

我们考虑的现象，第四代重夸克，这将是对产生在大型强子对撞机。我们表明，如果这样一个质量在400 GeV-600 GeV的夸克衰变为轻夸克和W玻色子，它将在许多通道中产生一个信号，这些信号可以在三代标准模型过程的背景上看到。特别是，这样的夸克可以在通道中看到，其中存在多个喷流，具有大的丢失动量和单个硬轻子，相反符号的硬轻子对或相同符号的轻子对。在同号双轻子通道中，几乎没有本底，因此，在大不变质量下，过量的这种对将表明重下型夸克的存在。更一般地说，在我们的研究中，我们用来确定我们考虑的每个通道中重夸克质量的主要工具是使用这种夸克衰变的运动学来解决未观察到的中微子的动量。我们展示了这是如何实现的，即使在运动学是欠确定的情况下，使用的近似，这是相当不错的，两个重夸克几乎是在质心框架中的休息。由于至少最轻的重夸克很可能以我们所考虑的方式衰变，这意味着它应该在LHC中被观察到。实际上，夸克之间的质量分裂预计小于$m_W$，因此如果第四代和更低代之间的Cabbibo-Kobayshi-Maskawa（CKM）矩阵元不太小，那么第四代夸克对的两个成员都将以这种方式衰变。如果是这样的话，这两个夸克的组合信号将使第四代的信号更加突出。

英文摘要：

We consider the phenomenology of the fourth generation heavy quarks which would be pair produced at the LHC. We show that if such a quark with a mass in the phenomenologically interesting range of 400 GeV--600 GeV decays to a light quark and a W-boson, it will produce a signal in a number of channels which can be seen above the background from the three generation Standard Model processes. In particular, such quarks could be seen in channels where multiple jets are present with large missing momentum and either a single hard lepton, an opposite sign hard lepton pair or a same sign lepton pair. In the same sign dilepton channel there is little background and so an excess of such pairs at large invariant mass will indicate the presence of heavy down type quarks. More generally, in our study, the main tool we use to determine the mass of the heavy quark in each of the channels we consider is to use the kinematics of the decay of such quarks to resolve the momenta of the unobserved neutrinos. We show how this can be carried out, even in cases where the kinematics is under-determined by use of the approximation, which holds quite well, that the two heavy quarks are nearly at rest in the center of mass frame. Since it is very likely that at least the lightest heavy quark decays in the mode we consider, this means that it should be observed at the LHC. Indeed, it is expected that the mass splitting between the quarks is less than $m_W$ so that if the Cabbibo-Kobayshi-Maskawa (CKM) matrix element between the fourth and lower generations are not too small, both members of the fourth generation quark doublet will decay in this way. If this is so, the combined signal of these two quarks will make the signal for the fourth generation somewhat more prominent.

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