Ricerca di violazione CP nel decadimento D0 -> pi+ pi- pi0 all'esperimento Belle II

The standard model (SM) of particle physics is the most successfully tested theory of nature at a fundamental level. Despite its tremendous accuracy in predicting the interactions among particles, it is unable to provide answers to several questions, including the origin of the matter-antimatter asymmetry of the universe: the violation of the charge-parity (CP) symmetry is necessary to explain it, but the observed amount at the particle level is insufficient, within the assumptions of the SM, to match the observations at the cosmological scale. There must exist, therefore, undiscovered sources of CP violation. Concerning quarks, CP violation has been measured extensively in the kaon and beauty sectors, and no clear discrepancy from the SM has been found. In the charm sector, instead, the SM predicts much smaller CP violation, and only in recent years have we achieved experimental sensitivity comparable to the SM predictions. Still, CP violation in the charm sector has only been observed in the D⁰ → π⁺π⁻ channel, and only by the LHCb experiment. This compels searches for CP violation in other channels and by other experiments. In my thesis, I present a measurement of the time-integrated CP asymmetry of the D⁰ → π⁺π⁻π⁰ decay channel using a datset of 428 fb⁻¹ collected by the Belle II experiment. The measurement is consistent with CP symmetry and with previous determinations by the BaBar and Belle experiments. Furthermore, this measurement improves the precision of the current world best (performed by the BaBar experiment) by 34%.