Search for rare top quark decays

Abstract

The top quark is the heaviest elementary particle known and has such a small lifetime that it decays before hadronization occurs, almost exclusively to bW, within the Standard Model (SM). These properties make it a good object to test quantum chromodynamics (QCD), in production, and electroweak sectors, in decay or single top production, of the SM of particle physics. In the SM, due to the GIM mechanism [1], Flavour Changing Neutral Current (FCNC) decays are forbidden at tree level and the decay rates are much smaller than the rate of the dominant decay mode t→ bW at loop level. Figure 1 shows the dominant decay of the top quark, as well as possible FCNC decays. However, several SM extensions predict higher branching ratios (BR) for the top quark FCNC decays [2] (Table 1) which make the search for FCNC decays a good window into physics beyond the SM. Examples of such extensions are the quark-singlet model (QS), the two-Higgs doublet model with (FC 2HDM) or without (2HDM) flavour-conservation, the minimal supersymmetric model (MSSM), SUSY with R-parity violation, the Topcolourassisted Technicolour model (TC2) [3] or models with warped extra dimensions (RS) [4].