CERN Accelerating science

The objective of this thesis is the search and study of diffractive events within the ALICE (A Large Ion Collider Experiment) detector at the CERN Large Hadron Collider (LHC). The LHC is designed to collide proton on proton (pp) at a center of mass energy LHC and lead on lead (Pb-Pb) at the center of mass energy per nucleon pair at very high luminosities. Even though ALICE was designed for the study and characterization of the quark gluon plasma, which is generated at heavy nuclei accelerators (like LHC), ALICE also takes data during pp collisions in LHC, the data taken during this period serves like a reference or the heavy ion phase, but also is used to perform analysis where ALICE is competitive with other LHC experiments. The cross sections of inelastic and diffractive processes in pp collisions are among the basic observables used to characterize the properties of interactions, for such reason, ALICE has a dedicated program to the study of diffractive events. During run 1 of LHC, ALICE presented a measurement of single and double diffractive cross sections, the results were consistent with all the comparisons made between other LHC experiments. During the Long Shut Down 2 of LHC, the ALICE collaboration installed a forward detector known as ALICE Diffractive Detector, AD for short. This detector increased ALICE capabilities in the selection of diffractive processes in pp collision events, also optimized the trigger efficiencies at minimum bias level. In the first two chapters of this thesis there is a brief introduction to the standard model of particle physics and a short description of the ALICE experiment together with the main LHC experiments. Since I found myself highly involved in the incorporation, maintenance and commissioning of ALICE Diffractive detector, in the third chapter I give a detailed description of this detector, along with some performance results during beam test at CERN facilities, and later on during pp collisions. As an extra, during my stay at CERN, I joined the effort for the measurement of the diffractive cross section at E= sort( 13 TeV), in the fourth chapter I present the results obtained in this analysis with 2015 pp data in ALICE. In the final section, there are some conclusions about the work done accompanied by a list of the publications obtained during the realization of this thesis.