Back in 1964, physicists experimenting with a particle known as the K meson and its antimatter equivalent, the anti-K meson, showed for the first time that antimatter can decay more rapidly than matter. (What scientists mean when they talk about a particle decaying is that it changes into something else. Most elementary particles are unstable, and within a fraction of a second after coming into existence they undergo a series of changes before finally reaching a stable form.)
Today, physicists believe a rare particle called the B meson, or B for short, is best suited to reveal the differences between matter and antimatter. Particles shed mass as they decay, with heavy particles turning into lighter ones. B mesons are especially heavy, which makes them ideal for asymmetry research. Think of it this way: Let's say you're planning a European vacation, starting from London and ending in Athens. If money is limited, you'll travel directly, making few stops in between. But if your budget is vast and you must spend it all, you'll visit a dozen countries along the way. Similarly, the B meson's abundant mass, and need to shed it, creates a range of disintegration pathways. Scientists watch the various ways in which it decays, then compare the end results, checking and cross-checking their findings for consistency.