Z. K. Jia

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 a circular accelerator, electrons are accelerated to nearly the speed of light and smash into positrons: their antiparticles. At the collision point, a burst of pure energy briefly appears, from which new particles are born. The BESIII detector, like a high-speed camera, captures the tracks of these short-lived guests.

When an electron and a positron collide at the BESIII collider, they produce a short-lived particle — the charmed baryon Λc+. Inside it, like in an overstuffed box, another particle quickly emerges: the Λ hyperon. This hyperon has its own rotation, its spin, and physicists have for the first time been able to measure how much that rotation is aligned with the particle's direction of motion.

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.

Inside the proton and neutron, life is boiling: quarks exchange gluons, and for an instant pairs of particles appear and vanish. Some of them, the so-called scalar mesons, live for only 10⁻²³ seconds — less time than light needs to cross an atomic nucleus.

The J/psi particle lives for an instant and then decays into lighter particles, much like a snapped string scattering into pieces. Physicists from the BESIII collaboration caught over ten billion such decays to figure out exactly what 'pieces' are produced.

In an accelerator near Beijing, electrons collide with positrons, and for an instant, particles are born that you wouldn't find in ordinary matter. One of them is lambda-c-plus: inside it sits a heavy charmed quark, like a stone in a slingshot. Now physicists have for the first time seen this particle break apart into a neutron, a positive pion, and an eta meson.

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.