Determining the dark matter particle mass through antler topology processes at lepton colliders

Abstract

We study the kinematic cusps and endpoints of processes with the "antler topology" as a way to measure the masses of the parity-odd missing particle and the intermediate parent at a high energy lepton collider. The fixed center of mass energy at a lepton collider makes many new physics processes suitable for the study of the antler decay topology. It also provides new kinematic observables with cusp structures, optimal for the missing mass determination. We also study realistic effects on these observables, including initial state radiation, beamstrahlung, acceptance cuts, and detector resolution. We find that the new observables, such as the reconstructed invariant mass of invisible particles and the summed energy of the observable final state particles, appear to be more stable than the commonly considered energy endpoints against realistic factors and are very efficient at measuring the missing particle mass. For the sake of illustration, we study smuon pair production and chargino pair production within the framework of the minimal supersymmetric standard model. We adopt the log-likelihood method to optimize the analysis. We find that at the 500 GeV ILC, a precision of approximately 0.5 GeV can be achieved in the case of smuon production with a leptonic final state, and approximately 2 GeV in the case of chargino production with a hadronic final state.