Instrumental Backgrounds to $t{ar t}$ and Single Top Production at Hadron Colliders

A number of backgrounds to top quark production at the LHC experiments (ATLAS and CMS) and the Tevatron experiments (CDF and D0) are characterized as instrumental: beam related-backgrounds, cosmic ray backgrounds, and backgrounds from non-prompt (or ``fake'') leptons. A number of strategies, have been deployed in the large experiments to minimize these backgrounds and to estimate their rate. The strategies span a wide range, at the level of the accelerator, the detector apparatus, the first few cuts which are typically common to many physics analyses, and also including more refined kinematic cuts and sophisticated data-driven techniques to estimate fake leptons. We present here a survey of the state of the art in the reduction of instrumental backgrounds and also their estimation.