RECO level √smin and subsystem √smin min: Improved global inclusive variables for measuring the new physics mass scale in ET events at hadron colliders

Abstract

The variable √smin was originally proposed in [1] as a model-independent, global and fully inclusive measure of the new physics mass scale in missing energy events at hadron colliders. In the original incarnation of √smin, however, the connection to the new physics mass scale was blurred by the effects of the underlying event, most notably initial state radiation and multiple parton interactions. In this paper we advertize two improved variants of the √smin variable, which overcome this problem. First we show that by evaluating the vsmin variable at the RECO level, in terms of the reconstructed objects in the event, the effects from the underlying event are significantly diminished and the nice correlation between the peak in the √smin(reco) min distribution and the new physics mass scale is restored. Secondly, the underlying event problem can be avoided altogether when the √smin concept is applied to a subsystem of the event which does not involve any QCD jets. We supply an analytic formula for the resulting subsystem √smin(sub) min variable and show that its peak exhibits the usual correlation with the mass scale of the particles produced in the subsystem. Finally, we contrast √smin to other popular inclusive variables such as HT , MTgen and MTTgen. We illustrate our discussion with several examples from supersymmetry, and with dilepton events from top quark pair production.