We study the possibility of detecting new physics (NP) phenomena at the LHC through a new search strategy looking at the monotop (top plus missing energy) signature which is common to a variety of NP models. We focus on the leptonic top decay mode and study the discovery or exclusion reach of the 2012 LHC data for three example models. Contrary to the hadronic mode, in this case the problematic QCD multijet background can be safely neglected. We find that the key kinematic variable to suppress most of the remaining SM backgrounds is the transverse mass of the charged lepton and missing energy. In fact, one could expect that the single-top production measurements already address the monotop signature in this mode. This is, however, not the case, because in the SM single-top production, the transverse mass has an end point determined by the $W$ mass, while the NP signals typically have an additional source of missing energy. We compare, under the same conditions, our monotop search strategy with existing single-top measurements and find a considerable improvement in the monotop signature reach.

• Received 8 November 2013

DOI:https://doi.org/10.1103/PhysRevD.89.014016