In the CMS detector at the Large Hadron Collider, protons accelerated to nearly the speed of light collided. Among billions of such collisions, physicists searched for a rare signature: the production of a single heavy particle that immediately decays into a W boson and a b quark. The W boson lives for a tiny fraction of a second and decays into an electron or muon, while the b quark turns into a jet of particles, like the shards of a broken cup scattering across a table.
Such a signature could reveal a 'vector-like quark'—a hypothetical heavy relative of the ordinary quarks that make up protons and neutrons. If it existed, its appearance would stand out against the background of ordinary processes. But after analyzing data accumulated over several years of collider operation, no excess of events was found. It's like listening to hundreds of hours of ocean noise and not hearing a single foreign sound.
Such constraints are like narrowing the search area on a map: the more precisely we know where a particle is not, the fewer places remain to look. Perhaps the next generation of experiments or more refined analysis methods will finally hear that sound in the noise.
Vector-like quarks, if found, would be the first known particles to acquire mass differently from all others — not through the Higgs mechanism.
In Liu Cixin's novel 'The Three-Body Problem,' physicists encounter particles that violate familiar laws — searching for exotic quarks is somewhat like trying to catch such an anomaly in a real experiment.