Search of supersymmetric particles in multi-jet events with missing energy

Many extensions of the Standard Model (SM) of particle physics predict the existence of TeV-scale strongly interacting particles that decay to weakly interacting descendants. Among them, Supersymmetry (Susy) is one of the most studied and a leading candidate theory for describing physics beyond SM since provides a consistent explanation to several theoretical concerns like the hierarchy problem of the SM. In the context of this theory, the strongly interacting parent particles are the partners of the quarks (squarks, q~) and gluons (gluinos, g~). If they are kinematically accessible, the squarks and gluinos could be produced in the proton-proton (pp) interactions at the Large Hadron Collider (LHC). This thesis presents the results of the search for new particles decaying to final states with large numbers (from at least 7 to at least 10) of jets together with significant missing transverse momentum and no isolated electrons or muons. The analysis is performed with a total integrated luminosity corresponding to 20.3 fb-1 of pp collision data at center-of-mass energy sqrt(s) = 8 TeV collected by the Atlas experiment at the LHC. The sensitivity of the search to identify possible Susy-like event candidates is enhanced by considering signal regions defined in terms of the number of b-tagged jets and the scalar sum of masses of large-radius jets in an event. These searches found no significant excess over the Stan- dard Model expectation. The results are interpreted in the context of an cMssm model and various simplified supersymmetry-inspired models. The exclusion limits substantially extend previous results constraining several supersymmetric models. For example, in a model where both of the pair-produced gluinos decay via gl → t + t~ + χ_0^1, gluino masses smaller than 1.1 TeV are excluded for neutralino (χ_0^1) masses below 350 GeV.