Dark matter particle spectroscopy at the LHC: Generalizing M_T2 to asymmetric event topologies

We consider SUSY-like missing energy events at hadron colliders and critically examine the common assumption that the missing energy is the result of two identical missing particles. In order to experimentally test this hypothesis, we generalize the subsystem M_T2 variable to the case of asymmetric event topologies, where the two SUSY decay chains terminate in different "children particles. In this more general approach, the endpoint M_T2(max) of the M_T2 distribution now gives the mass̃M_p( ̃M_cM^(a) , ̃M (b)c ) of the parent particles as a function of two input children masses ̃M _cM^(a) and̃M_cM^(b) . We propose two methods for an independent determination of the individual children masses M(a) c and M(b) c . First, in the presence of upstream transverse momentum PUTM the corresponding functioñM_p( ̃M_cM ^(a) ,̃M_cM^(b) , PUTM) is independent of PUTM at precisely the right values of the children masses. Second, the previously discussed M_T2 "kink" is now generalized to a "ridge" on the 2-dimensional surfacẽM_p( ̃M _cM^(a) ,̃M_cM^(b) ). As we show in several examples, quite often there is a special point along that ridge which marks the true values of the children masses. Our results allow collider experiments to probe a multi-component dark matter sector directly and without any theoretical prejudice.