Authors: David Atwood Sudhir Kumar Gupta Amarjit Soni
Publish Date: 2012/06/19
Volume: 2012, Issue: 6, Pages: 105-
Abstract
Although there is no compelling evidence at present against the Standard Model SM in the past few years a number of 23 sigma tensions have appeared which could be alleviated simply by adding another generation of fermions Furthermore a fourth generation could help resolve the issue of baryogenesis and the understanding of the hierarchy problemIn this paper 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 GeV600 GeV decays to a light quark and a Wboson 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 pairIn 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 underdetermined by use of the approximation which holds quite well that the two heavy quarks are nearly at rest in the center of mass frameSince 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 CabbiboKobayshiMaskawa 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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