Sfermion Interference in Neutralino Decays at the LHC

If the two lightest neutralinos of the Minimal Supersymmetric Standard Model have a mass splitting less than the Z boson mass, interference effects in the three-body decay chi_2^0 --> chi_1^0 f f can be important. We formulate an observable that contains information on the nature of the interference: the ratio BR(chi_2^0 --> chi_1^0 b b) / BR(chi_2^0 --> chi_1^0 l+ l-). This will give a constraint on the supersymmetry breaking parameters that is complementary to many techniques already existing in the literature. We present some ideas on how to perform a simple counting experiment to determine this ratio.