the invisible particle as follows: $$\mT(\mathrm{q}, \ptvecmiss) \equiv \sqrt{2 \pt^{\mathrm{q}} \ptmiss [1 - \cos \Delta\phi(\ptvec^{\mathrm{q}}, \ptvecmiss)]}.\label{eq:MT}$$ We use as a discriminant the sum of the transverse masses calculated for each with , [$\Sigma\mT$]{}, given by $${\ensuremath{\Sigma\mT}\xspace}= \mT({\tauh^{(1)},\ptvecmiss}) + \mT({\tauh^{(2)},\ptvecmiss}).$$ Another variable found to be useful in the discrimination of signal from background is the “stransverse mass"  [@MT2variable; @MT2variable2; @MT2variable3]. This mass variable is a generalization of in the case of multiple invisible particles. It serves as an estimator of the mass of pair-produced particles when both particles decay to a final state containing the same invisible particle. It is given by: $$\mTii = \min_{\ptvec^{\mathrm{X}(1)} + \ptvec^{\mathrm{X}(2)} = \ptvecmiss}
  \left[ \max \left( \mT^{(1)} , \mT^{(2)} \right) \right],
\label{eq:MT2}$$ where $\ptvec^{\mathrm{X}(i)}$ (with $i$=1, 2) are the unknown transverse momenta of the two undetected particles, X(1) and X(2), corresponding to the neutralinos in our signal models, and $\mT^{(i)}$ are the transverse masses obtained by pairing either of the two invisible particles with one of the two leptons. The minimization ($\min$) is over the possible momenta of the invisible particles, taken to be massless, which are constrained to add up to the in the event. For direct pair production, with each decaying to a 