Study of supersymmetric signals with R-parity violation in ATLAS at LHC

Supersymmetry (SUSY) is one of the most promising theories providing a solution for many of the current open questions in the Standard Model (SM). Among the several possible scenarios that SUSY presents, there is a particularly interesting one due to its relation with neutrino physics. In this model the spontaneous breaking of R-parity gives vacuum expectation values (vevs) to neutrinos, providing a “vev-seesaw” mechanism that leads to neutrino masses. Below the scale of these vevs, R-parity breaking is explicit through bilinear lepton number violating terms. The same parameters that induce neutrino masses and mixings are responsible for the decay of the lightest supersymmetric particle (LSP). In this thesis two studies have been developed in order to search for a proof on the existence or not of SUSY with bilinear R-parity violation (bRPV) in Nature, within the accessible mass range. The first part of the thesis is devoted to the determination of the discovery potential of the bRPV model in the ATLAS detector at the Large Hadron Collider (LHC) and to the possible measurement of the LSP mass, at three different working centre-of-mass energies for the LHC of $\sqrt{s} =$ 7, 10 and 14 TeV. Since one of the characteristics of this model is the presence of muons in a large percentage of events and by high jet multiplicity, the optimal approach for its search is to consider one muon and several jets in the final state. In this case, a search implying one muon and two jets is presented using Monte Carlo (MC) simulated samples of bRPV-SUSY and SM background. This work is documented in an ATLAS Internal Note (ATL-PHYS-INT-2010-042). The second part of the thesis is an inclusive search for bRPV with real ATLAS data taken from 2011 LHC collisions at 7 TeV, considering a grid of points in the bRPV parameter space. In this analysis, final states containing one muon and at least three or four jets are selected. After taking into account all possible sources of uncertainties, no significant excess of events has been observed over the expected SM background. This has led to the first hadron colliders exclusion limits set on bRPV models, which has been published in Physical Review D (Phys. Rev. D85 (2012) 012006; arXiv:1109.6606/hep-ex) and documented in detail in an ATLAS Internal Note (ATL-PHYS-INT-2011-082).