D⁰, or D-zero, is a type of meson, which is a subatomic particle made up of a quark and an antiquark. Specifically, it consists of a charm quark and an up antiquark. D⁰ mesons are important in particle physics because they help scientists study the behavior of quarks and the forces that govern their interactions. D⁰ mesons can decay into various other particles, making them a key focus in experiments at particle accelerators like the Large Hadron Collider or the Fermilab. Studying D⁰ decays provides insights into CP violation, a phenomenon that helps explain the matter-antimatter asymmetry in the universe.