In an underground ring 27 kilometers in circumference, protons are accelerated to nearly the speed of light and smashed head-on. At the collision point, conditions briefly recreate those of the first trillionth of a second after the birth of the universe. The CMS detector (a multi-story machine of silicon, lead, and superconducting magnets) captures the debris of these collisions.
Among the debris, physicists search for traces of W and Z bosons — particles that carry the weak force, which makes the Sun shine and some nuclei decay. They measure them with precision down to fractions of a percent: how often they are produced, at what angles they fly apart, how quickly they decay. Such precision makes it possible to spot the slightest deviation from theory, if any exists.
The most sensitive test is the electroweak mixing angle. It shows how electricity and the weak force are intertwined. A deviation of one-thousandth of a radian would mean new physics: unknown particles or extra dimensions. So far, everything agrees with predictions, but the precision is such that even a weak signal would be noticed.
Proton collisions are a blunt instrument compared to clean electron beams, but they provide enormous statistics. Billions of events allow random fluctuations to be averaged out and a signal to be extracted that would otherwise drown in noise. Thus the collider becomes a microscope for the most fundamental laws of nature.
The proton collision energy at the Large Hadron Collider, 13.6 TeV, is equivalent to the energy of a flying mosquito, but compressed into a volume a million billion times smaller than a grain of sand.
In the series "Dark Matter," a collider is used to search for particles that explain the hidden mass of the universe, just like the real experiments at CMS.