Production of the new pixel detector for the upgrade of the CMS experiment and study of anomalous couplings in the non-resonant Higgs bosons pair production in p-p collisions at $\sqrt{s}$ = 13 TeV

The present Ph.D thesis describes the work done within the CMS collaboration on the pixel detector upgrade and on the search for non-resonant di-Higgs production in p-p collision at LHC. The CMS upgrade project foresees, inter alia, the production of a new pixel detector (CMS Phase 1 Pixel Upgrade) to be commissioned at the beginning of 2017. Crucial part of the upgrade is the new readout chip (ROC) for the silicon sensor, psi46digV2respin, designed at the Paul Scherrer Institute (PSI) with a 250 nm CMOS technology. The thesis concerns the study and the development of test procedures for this new readout chip. Thanks to a long stay at PSI, I could provide an important contribution to the debug phases of the first version of the ROC and TBM, the chip that handles the various ROCs in the pixel module, and to the development of the software used by the whole collaboration for the ROC and module testing. Furthermore, I managed the ROC wafers test from the early project phases. The ROCs are produced on silicon wafers and undergo various processes before being assembled on the modules, e.g., metal deposition on the pixel pads, thinning and dicing. These processes lead mechanical and thermal stresses that can damage the chips. The ROC wafers test has thus been performed following the same procedure before and after the processing, in order to minimize the failing ROCs fraction mounted on the modules. It has been measured that the processing introduces a 5.2% reduction of the number of perfectly working ROCs. The pixel detector production line, the module qualification process and the ROC wafers test results are reported in this thesis. The modifications performed on the ROC-sensor connection technology are also described. The new pixel detector installation will allow an increment of the CMS tracking performance that, together with the planned increment of the luminosity (a factor 35 between 2017 and the current value) could allow access to physical processes with a low cross section and a high number of b quarks in the final states. For this purpose, a preliminary study on the non-resonant Higgs bosons pair production in the fully hadronic decay channel (bb bb) is here presented. The study has been performed analysing the data collected by the CMS experiment in 2015, equal to 2.19 fb-1, in proton-proton collision at energy in the centre of mass (√s) of 13 TeV. The data collected in 2015 do not allow to set a reasonable exclusion limit on the cross section of this process and the analysis will be completely developed in 2016 and following years. The study of the Higgs bosons pairs production is relevant because the pairs can be produced also after couplings which are not allowed by the Standard Model (anomalous), such as the higgs-gloun contact interaction. These anomalous couplings lead to an increment of the cross section of the process and to differences in the kinematics of the final states. The process of Higgs bosons pairs production via anomalous couplings is described by a Lagrangian with five free parameters. This implies a difficulty in the identification of parameter space points to be experimentally investigated. I developed an analysis technique which allows, by studying simulated samples, to divide the parameter space in kinematically similar regions and to identify a benchmark in each of them. The distance among different points of the parameter space has been defined through a binned likelihood ratio and an iterative algorithm has been developed to group them together. Twelve regions which are kinematically equivalent have been identified in a 5-D space. The results of this study, described in this thesis, are collected in an article which is under publication on JHEP and they will be considered as guideline for the searches of non-resonant Higgs bosons pair production at CMS.