L. Q. Lin

At a particle accelerator in Beijing, electrons collide with positrons, and for a fleeting moment, a particle called eta-c is born. It lives for a tiny fraction of a second and then decays into other particles. One of the rarest paths is to split into two photons, particles of light. Until now, no one could say exactly how often this happens.

Two twins look identical, but one is left-handed and the other right-handed. In the world of elementary particles, there are similar pairs: Ξ- and its antiparticle Ξ+. They are born together in the decay of the J/ψ particle and, like entangled twins, maintain a connection even at a distance.

In the accelerator, an electron and a positron collide, and for an instant, a particle is born that lives for less than a billionth of a second. Its decay resembles the explosion of a tiny firecracker: fragments scatter in all directions, and physicists reconstruct what was inside from their trajectories.

Among the debris of particle collisions, short-lived 'guests' sometimes appear — hyperons. One of them, Σ0, lives for less than one ten-billionth of a second and decays on the fly. Catching it directly is nearly impossible, but its traces can be spotted: it leaves behind another particle, Λ, and an electron-positron pair.