variable has a kinematic endpoint at the same underlying mass scale as the ${\ensuremath{M_R}\xspace}$ mean value. The ratio ${\ensuremath{R}\xspace}$ quantifies the flow of energy in the plane perpendicular to the beam and the partitioning of momentum between visible and invisible particles.

-   The shapes of the distributions in the (${\ensuremath{M_R}\xspace}$, ${\ensuremath{R^2}\xspace}$) plane are described for the SM processes. Razor variable distributions exhibit peaks for most SM backgrounds, as a result of turn-on effects from trigger and selection thresholds as well as of the relevant heavy mass scales for SM processes, namely the top quark mass and the $\PW$ and $\cPZ$ boson masses. However, compared with signals involving heavier particles and new-physics sources of , the SM distributions peak at smaller values of the razor variables. For values of the razor variables above the peaks, the SM background distributions (and also the signal distributions) exhibit exponentially falling behavior in the (${\ensuremath{M_R}\xspace}$, ${\ensuremath{R^2}\xspace}$) plane. Hence, the asymptotic behavior of the razor variables is determined by a combination of the parton luminosities and the intrinsic sources of . The multijet background from processes described by quantum chromodynamics (QCD), which contains the smallest level of intrinsic amongst the major sources of SM background, has 