The ALICE experiment: $\rm D^{+}$-meson production in heavy-ion collisions and silicon low noise sensors characterization for the ITS Upgrade.

This thesis collects my work on two aspects of the ALICE experiment at the Large Hadron Collider: the measurement of $\rm D^{+}$-meson production in Pb-Pb collisions at $\sqrt{s_{\rm {NN}}}= 2.76$ TeV and the characterization of silicon low noise sensors for the Inner Tracking System Upgrade. I worked within the INFN group of Torino that it is involved in the ALICE experiment both in the physics program related to the study of heavy-flavour production and in the project of the ITS Upgrade. ALICE is one of the main experiment of the LHC and it is the only one optimized to study ultra-relativistic heavy-ion collisions. The main goal is to study the properties of the Quark Gluon Plasma (QGP), a phase of matter where quarks and gluons are deconned. Heavy quarks are a powerful tool to study such properties because they can be created only in hard scattering processes at the initial stage of the collision and, subsequently, they interact with the QGP. The measurement of charmed meson production in Pb-Pb collisions allows to assess final state eects due to the formation of the QGP. One of the physical observable studied is the nuclear modication factor ($R_{\rm {AA}}$). It quantifies the modication of the D-meson momentum distribution in nucleus-nucleus collisions with respect to the one in proton-proton collisions. The results of the $\rm D^{+}$-meson $R_{\rm {AA}}$, obtained with the Pb-Pb data sample collected in 2011 by ALICE, will be presented in this thesis. However, a more precise measurement, in term of both statistical and systematic uncertainties, would be fundamental for a complete understanding of the properties of the medium and its components. For this reason, an upgrade of the ALICE apparatus and, in particular of the ITS, is planned to be installed during the second long shutdown of LHC in 2019. The goal is to enhance the ALICE physics capabilities and, expecially, the tracking performance for heavy-flavour detection. To overcome the limitations of the present ITS, a different technology has been chosen for the layers of the upgraded detector: Monolithic Active Pixels Sensors. They can offer the granularity and the material budget needed to fulfil the requirements of the new ITS. Several prototypes have been developed to find the best solution, hence an intensive characterization campaign has taken place. I contributed in the characterization of small-scall prototypes of MIMOSA sensors, developed at IPHC (Strasbourg), and in the characterization of a full-scale prototype of pALPIDE-v2, developed by a collaboration formed by CCNU (China), CERN, INFN (Italy) and Yonsei (South Corea). The first sensors have been characterized in the framework of the development of a testbeam telescope at the LNF (Frascati, Italy).