A model-independent ''general search'' for new physics with the ATLAS detector at LHC

The LHC particle collider accelerates bunches of protons at energies never reached before, thus opening a completely new landscape of new physics. In this scenario the number of possible physics processes and signatures becomes virtually infinite, making the setup of dedicated analyses impossible. Moreover there are regions of the phase-space where signals of new physics are not very likely to be found, or where suitable theoretical models are missing, and it is important to be able to reveal new processes from such regions as well. At the time this Thesis was started, no model-independent analysis had been set for the ATLAS experiment at LHC. The goal of this work was then to conceive and develop a new model-independent ''General Search'' for ATLAS, and to explore its possibilities. The new analysis has been then implemented and run over the first data which have been collected by the ATLAS experiment at a centre-of-mass energy of 7 TeV. This work presents the motivation of the data analysis, describes its implementation and shows the results. The data have shown a very good agreement with the Standard Model expectation and no evidence of new physics has been observed. Nevertheless, an efficient strategy and methodology for a new model-independent ''General Search'' have been defined and they are ready to be used in a next version of this analysis, over a larger set of experimental data. During this work, a new innovative software framework has been also conceived and developed to ease the implementation of physics analysis code using Computer-Aided- Software-Engineering (CASE) principles. The framework has been successfully used to analyze the very first LHC data, and then it has been transformed into an open-source modular framework for HEP data analysis, and presented at Physics and Computer Science international conferences.