Neutralino decays at the CERN LHC

We study the distribution of lepton pairs from the second lightest neutralino decay ̃ \~χ₂⁰→ ̃ \~χ₁⁰l⁺l^-. This decay mode is important to measure the mass difference between ̃ \~χ₂⁰ and the lightest neutralino ̃ \~χ₁⁰, which helps to determine the parameters of the minimal supersymmetric standard model at the CERN LHC. We found that the decay distribution strongly depends on the values of underlying MSSM parameters. For some extreme cases, the amplitude near the end point of the lepton invariant mass distribution can be suppressed so strongly that one needs the information of the whole mₗₗ distribution to extract m_ ̃ \~χ₂⁰-m_ ̃ \~χ₁⁰. On the other hand, if systematic errors on the acceptance can be controlled, this distribution can be used to constrain slepton masses and the Z ̃ \~χ₂⁰ ̃ \~χ₁⁰ coupling. Measurements of the velocity distribution of ̃ \~χ₂⁰ from samples near the end point of the mₗₗ distribution, and of the asymmetry of the pT of leptons, would be useful to reduce the systematic errors.