How to Look for Supersymmetry under the LHC Lamppost

We apply a model-independent, agnostic approach to the collider phenomenology of supersymmetry, in which all mass parameters are taken as free inputs at the weak scale. We consider the gauginos, Higgsinos, and the first two generations of sleptons and squarks, and analyze all possible mass hierarchies among them ($4\times 8!=161280$ in total) in which the lightest superpartner is neutral, leading to missing energy. In each case, we identify the full set of the dominant decay chains originating from the lightest colored superpartner. Our exhaustive search reveals several quite dramatic yet unexplored multilepton signatures with up to 8 isolated leptons (plus possibly up to 2 massive gauge or Higgs bosons) in the final state. Such events are spectacular, background-free for all practical purposes, and may lead to a discovery in the very early stage ($\sim 10{\mathrm{pb}}^{-1}$) of LHC operations at 7 TeV.

Figure 1

Graphical representation of the allowed transitions between the SUSY states from Table . One (two, three) parallel lines represent two- (three-, four-) body decays. The relative suppression of each decay mode is indicated by the line type. The identity of the resulting SM decay products is denoted by the line color: red for a jet $j$, blue for a lepton $\ell$ and green for a massive boson $v\equiv \{W^{\pm },Z,h\}$ (which may be either on-shell or off-shell).

Figure 2

A slice through the MSUGRA parameter space for fixed $A_0=0$, $\tan \beta =10$ and $\mu >0$. Yellow shaded regions are ruled out by direct searches at LEP or by requiring a neutral LSP. The remaining area is color-coded according to the sparticle hierarchy type (1). The solid black lines delineate regions with the same maximally leptonic $\mathcal{C}$ decay mode.

Figure 3

Inclusive cross sections (in fb) at the LHC for 8 lepton events from the exclusive chain in (2) for the study points from Table  (solid lines); inclusive cross sections for left-handed squark pair production (dotted); and cumulative branching fraction of the 8 lepton final state (dashed, read on the right).

Figure 4

(Stacked) number of multilepton events in $1{\mathrm{fb}}^{-1}$ of data at a 7 TeV LHC, for the $xxGQWLBEH$ sparticle hierarchy with the mass spectra shown in Table .