Bubble Chamber Event. Resonances last typically for a mere 10 (-23 power) s and therefore leave no discernible track in a bubble chamber. But by calculating back from the energies and angles of the particles that are detected, physicists can infer that a resonance has existed. In this picture from a bubble chamber at Berkley, an antiproton, coming from below, annihilates with a proton to produces two negative pions, a neutral pion and two positive pions. The negative pions move off to the left, the positive pions to the right, while the pi-zero is undetected. The lower pi-plus decays to a muon, the short piece of track, and then to a positron, which curls out of the picture. The information in the picture ins consistent with the lower-energy pions, the lower tracks on left and right-being the decay products of a resonance state known as the omega.