Search for tZq Using BDT
- A search for the associated production of a top quark and a Z boson (tZq), as predicted by theory was performed with the full CMS data set collected at 8TeV.
- In order to enhance the separation between signal and background processes, a multivariate discriminator is used in both the tZq-SM and FCNC searches.
- A range of different quantities are used as input variables for the BDTs. They are selected based on their discriminating power and include kinematic variables related to the top quark and the Z boson
- The BDTs are trained using half of the simulated samples for these processes and they are trained separately for each channel. The output discriminant distribution is then fitted, in the signal region, for each channel, to determine whether there are any signal events present in the data.
- The signal is extracted by performing a simultaneous binned maximum-likelihood fit to the distributions of the signal samples and the background- enriched control region, using the two different discriminators.
- Different sources of systematic uncertainty that can affect the number of events passing the selection and the shape of the BDT response are considered.
