Kinematic Discrimination of tW and tt Productions Using Initial State Radiation

Production of a single top quark provides excellent opportunity for understanding top quark physics and Cabibbo-Kobayashi-Maskawa structure of the quark sector in the Standard Model. Although an associated production with a b-quark has already been observed at the Tevatron in 2009, a single top production in association with a W gauge boson has not been observed till 2014 at the LHC, where pair production of the top quark serves as the dominant background. Due to the kinematic similarity between tW and the dominant background, it is challenging to find suitable kinematic variables that offer good signal-background separation, which naturally leads to the use of multivariate methods. In this paper, we investigate kinematic structure of tW+j channel using M_T2 and invariant mass variables, and find that tW +j production could well be separated from tt production with high purity at a low cost of statistics when utilizing these kinematic correlations.