Dark matter particle spectroscopy at the LHC: generalizing M T2 to asymmetric event topologies
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Abstract
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 mass $$ {\tilde M_p}\left( {\tilde M_c^{(a)},\tilde M_c^{(b)}} \right) $$ of the parent particles as a function of two input children masses $$ \tilde M_c^{(a)} $$ and $$ \tilde M_c^{(b)} $$ . 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 function $$ {\tilde M_p}\left( {\tilde M_c^{(a)},\tilde M_c^{(b)},{P_{\text{UTM}}}} \right) $$ 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 surface $$ {\tilde M_p}\left( {\tilde M_c^{(a)},\tilde M_c^{(b)}} \right) $$ . 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.