Diego Tonelli

These plots show the effective lifetime asymmetries as function of decay time for D →K+K– (top) and D → π+π– (bottom) samples. Results of the fits not allowing for (dotted red line) and allowing for (solid blue line) CP violation are overlaid. Physicists gave funny names to the heavy quark cousins of those that make up ordinary matter: charm, strange, bottom, top. The Standard Model predicts that the laws governing the decays of strange, charm and bottom quarks differ if…

Mass distributions of the charm (left) and anticharm (right) decays used in the measurement. The different heights of the narrow peaks indicate instrumental and physics asymmetries. Among quarks, the charm has played probably the biggest role in the development of the Standard Model. When its existence was postulated in 1970 to explain the absence of particle decays that should have otherwise been observed, not many physicists believed charm could be real. But it is, as it was spectacularly shown by…

In 1979, a group of American, Japanese and Italian scientists began designing the Collider Detector at Fermilab (CDF), aimed at discovering the heavy carriers of the weak force, called W and Z particles. It turns out that CDF arrived slightly late for Ws and Zs, but the detector soon earned its spot in the particle physics race by discovering the heaviest elementary particle known to this day – the top quark. At the start, nobody had a clue that CDF,…

Up until 1964, physicists believed that the laws of physics governing our universe were identical by interchanging particles with their antiparticles (C symmetry or charge reversal invariance) and by observing the particles through a mirror (P symmetry or mirror symmetry). This was not the case. Physicists discovered that a type of meson called a kaon violates this charge-parity (CP) symmetry and that other heavier cousins, called B mesons, show even larger violations. CDF looked at CP violation in B meson…

This is the signal from the decay of a Λb particle into a Λ particle and a pair of muons, observed with a significance of 5.8 sigma. We know to be mindful of the geese around the Fermilab site, but penguins? Yes, they’re here, and they can be aggressive, especially against the Standard Model. Penguin decays, which take their name from their diagramed shape, are a class of particle decays important in indirect searches for new particles or interactions at…