\sqrt{s}_min: a global inclusive variable for determining the mass scale of new physics in events with missing energy at hadron colliders

TL;DR

The paper introduces xts_{min}, a new inclusive variable to estimate the mass scale of new particles in collider events with missing energy, providing a model-independent and accurate method.

Contribution

It defines xts_{min} as a simple formula related to measured energies and momenta, linking its distribution peak to the parent particle mass threshold, enabling model-independent mass determination.

Findings

xts_{min} correlates with the parent particle mass threshold.

Mass measurement accuracy is typically within a few percent.

Method remains effective despite initial state radiation effects.

Abstract

We propose a new global and fully inclusive variable \sqrt{s}_{min} for determining the mass scale of new particles in events with missing energy at hadron colliders. We define \sqrt{s}_{min} as the minimum center-of-mass parton level energy consistent with the measured values of the total calorimeter energy E and the total visible momentum \vec{P}. We prove that for an arbitrary event, \sqrt{s}_{min} is simply given by the formula \sqrt{s}_{min}=\sqrt{E^2-P_z^2}+\sqrt{\met^2+M_{inv}^2}, where M_{inv} is the total mass of all invisible particles produced in the event. We use t\bar{t} production and several supersymmetry examples to argue that the peak in the \sqrt{s}_{min} distribution is correlated with the mass threshold of the parent particles originally produced in the event. This conjecture allows a determination of the heavy superpartner mass scale (as a function of the LSP mass) in a completely general and model-independent way, and without the need for any exclusive event reconstruction. In our SUSY examples of several multijet plus missing energy signals, the accuracy of the mass measurement based on \sqrt{s}_{min} is typically at the percent level, and never worse than 10%. After including the effects of initial state radiation and multiple parton interactions, the precision gets worse, but for heavy SUSY mass spectra remains 10%.