Three Protons Detected Together for the First Time express
Three billiard balls scatter across the table after a strike: their trajectories depend only on the initial push. But in the world of atomic nuclei, things are more complex: particles sense each other on the fly, even if they are not bound together. For a long time, physicists could only measure pairwise interactions, while what happens when three meet remained behind the scenes.
In the ALICE experiment at the Large Hadron Collider, protons were collided at an energy of 13.6 TeV, and for the first time, a signal from three protons produced together was isolated. To do this, a new data-cleaning method was applied, similar to picking out the conversation of three specific people from the noise of a crowd. The measured correlation function showed that the nuclear interaction works even at high angular momenta and parity, creating an effective attraction at long distances.
The result turns three-body femtoscopy into a full-fledged tool for studying three-body forces. And since modern colliders produce many hyperons (particles with a strange quark), the method can be extended to systems involving strangeness. There is a chance to peek into three-body dynamics where there were only guesses before.
The three protons studied in the experiment were never part of a single nucleus: they were born in a collision and existed as a free trio for only an instant.
In Liu Cixin's novel "The Three-Body Problem," the chaotic motion of three stars makes a planet uninhabitable, but in the quantum world, trios of particles can exhibit unexpected orderliness.