Flavor changing neutral currents of top quarks at the LHC, a probe for new physics

May 18, 2016, 4:00 PM





When one observes the phenomena in our universe, one notices that the Standard Model (SM) fails to explain several outstanding problems, such as dark matter or dark energy. These shortcomings can be addressed by new physics extensions including new particles and symmetries at higher energy scales. At present, the hope is that unambiguous signals for such new physics will be discovered in the next runs of the LHC at CERN. Direct searches for new particles at the LHC, with distinct signatures such as missing energy final states, might be beyond the kinematic reach of the LHC. However, these particles can still contribute to the observed final states at loop-level altering the expected kinematics in the SM. In general, these processes are suppressed, typically at the order of the inverse mass squared of the new particle. Therefore, this suppression could be so high that the process may still missed at the LHC. In both cases, direct or indirect observation of new physics would yield a breakthrough towards understanding the completion of the SM. Flavor changing neutral currents (FCNC) processes, fall in the latter case and are an important probe for new physics. These processes contain at least two generations of fermions in the initial and final states and are suppressed in the SM by the Glashow-Iliopoulis-Maiani (GIM) mechanism. By extending the SM, one can build new physics models where the contributions of these processes are three orders of magnitude larger than those of the SM (e.g. 2HDM) and thus observable at the LHC. Thus, even if direct detection of new particles fails at the LHC, one may still expect indirect contributions in the SM sector. FCNC processes involving top quarks have been sought in the decays of top quarks to an up or charm quark and a scalar boson (e.g. H boson) or in the decay of a top quark into an up or charm quark and a vector boson (e.g. Z boson). In my talk I shall discuss the current state of these searches at the CMS experiment and will compare these to other experiments.

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