Wedgebox analysis of four-lepton events from neutralino pair production at the LHC

Abstract

A ‘wedgebox’ plot is a two-dimensional scatter-plot of two invariant mass quantities. Here pp→e+e-μ+μ-+≠E signature LHC events are analyzed by plotting the di-electron invariant mass versus the di-muon invariant mass. Data sets of such events are obtained across the MSSM input parameter space in realistic event-generator simulations, including cuts designed to remove SM backgrounds. Their study reveals several general features. Firstly, regions in the MSSM input parameter space where a sufficient number of events are expected so as to be able to construct a clear wedgebox plot are delineated. Secondly, the presence of box shapes on a wedgebox plot either indicates the presence of heavy Higgs bosons’ decays or restricts the location to a quite small region of low μ and M2 values, ≲ 200 GeV, a region denoted as the ‘lower island’. In this region, wedgebox plots can be quite complicated and change in pattern rather quickly as one moves around in the (μ,M2) plane. Thirdly, direct neutralino pair production from an intermediate Z0* may only produce a wedge shape since only \(\widetilde{\chi}_2^0\widetilde{\chi}_3^0\) decays can contribute significantly. And fourthly, a double-wedge or wedge-protruding-from-a-box pattern on a wedgebox plot, which results from combining a variety of MSSM production processes, yields three distinct observed endpoints, almost always attributable to \(\widetilde{\chi}_{2,3,4}^0 \to\widetilde{\chi}_1^0 \ell^+\ell^-\) decays, which can be utilized to determine a great deal of information about the neutralino and slepton mass spectra and related MSSM input parameters. Wedge and double-wedge patterns are seen in wedgebox plots in another region of higher μ and M2 values, denoted as the ‘upper island’. Here the pattern is simpler and more stable as one moves across the (μ,M2) input parameter space.