Mass Determination of New States at Hadron Colliders

TL;DR

The paper introduces a new kinematic method for accurately determining the masses of new particles at hadron colliders, especially effective with limited event data, by fitting entire distribution shapes rather than just endpoints.

Contribution

It presents an improved mass determination technique that uses full distribution fitting and applies it to LHC scenarios, achieving high precision with few events.

Findings

Masses can be determined within about 6 GeV accuracy.

Method is effective with as few as 250 events.

Applicable to rare processes like neutralino pair production.

Abstract

We propose an improved method for hadron-collider mass determination of new states that decay to a massive, long-lived state like the LSP in the MSSM. We focus on pair produced new states which undergo three-body decay to a pair of visible particles and the new invisible long-lived state. Our approach is to construct a kinematic quantity which enforces all known physical constraints on the system. The distribution of this quantity calculated for the observed events has an endpoint that determines the mass of the new states. However we find it much more efficient to determine the masses by fitting to the entire distribution and not just the end point. We consider the application of the method at the LHC for various models and demonstrate that the method can determine the masses within about 6 GeV using only 250 events. This implies the method is viable even for relatively rare processes at the LHC such as neutralino pair production.