Pair-produced heavy particle topologies: MSSM neutralino properties at the LHC from gluino/squark cascade decays

Processes of the form pp -> anything -> XiXj -> x (x) over bar + y (y) over bar (+E) are studied via a technique that may be viewed as an adaptation of time-honoured Dalitz plot analyses. X-i and X-j are new heavy states (with i, j=1,..., n), which may be identical or distinct; and x (x) over bar and y (y) over bar are necessarily distinct standard model (SM) fermion pairs whose invariant masses can be measured. A Dalitz-like plot of said invariant masses, M(x (x) over bar) versus M(y (y) over bar), exhibits a topology connected to the masses and specific decay chains of X-i and X-j. Aside from relatively minor details, observed patterns consist of a collection of box and wedge shapes. This collection is model-dependent: comparison of the observed pattern to the possibilities for a specific model yields information on which new particle pair combinations are actually being produced, information beyond that extractable from conventional one-dimensional invariant mass distributions. The technique is illustrated via application to the minimal supersymmetric standard model (MSSM) process pp ->, (g) over tilde $(g) over tilde $, (g) over tilde $(q) over tilde $, (q) over tilde $(q) over tilde $ -> (X) over tilde (0)(i) (X) over tilde (0)(j) -> e(+)e(-) + mu(+)mu(-) (+E). Here the heavy states are neutralinos (X) over tildei(0) (i=2,3,4)-note that (X) over tilde (0)(1) is excluded - which are produced in gluino/squark ((g) over tilde $/(q) over tilde $) cascade decay chains. Even with fairly modest expectations for the LHC performance during the first few years, this method still provides substantial insight into the neutralino mass spectrum and couplings if gluino/squark masses are relatively low (similar or equal to 400 GeV).