Measurement of SUSY masses via cascade decays for SPS 1a

TL;DR

This work investigates measuring SUSY particle masses from cascade decays at the LHC using kinematic endpoints of invariant-mass distributions in the SPS 1a framework. It derives analytic endpoint formulas and inversion relations, analyzes their applicability across mSUGRA parameter space, and validates mass extraction through extensive ATLAS-like simulations combined with DF background subtraction and various jet-lepton selection strategies. The study reveals that endpoint-based mass determination can be highly precise for favorable hierarchies, but mass ambiguities and border effects can yield multiple minima; incorporating a Linear Collider input dramatically fixes the mass scale and suppresses degeneracies, greatly enhancing overall precision. The results provide practical guidance for exploiting cascade endpoints in SUSY searches and emphasize the importance of cross-experiment data and robust fitting methods for reliable mass reconstruction.

Abstract

If R-parity conserving supersymmetry exists below the TeV-scale, new particles will be produced and decay in cascades at the LHC. The lightest supersymmetric particle will escape the detectors, thereby complicating the full reconstruction of the decay chains. In this paper we expand on existing methods for determining the masses of the particles in the cascade from endpoints of kinematical distributions. We perform scans in the mSUGRA parameter space to delimit the region where this method is applicable. From the examination of theoretical distributions for a wide selection of mass scenarios it is found that caution must be exerted when equating the theoretical endpoints with the experimentally obtainable ones. We provide analytic formulae for the masses in terms of the endpoints most readily available. Complications due to the composite nature of the endpoint expressions are discussed in relation to the detailed analysis of two points on the SPS~1a line. Finally we demonstrate how a Linear Collider measurement can improve dramatically on the precision of the masses obtained.