ATLAS Collaboration

Inside protons accelerated to nearly the speed of light, a particle heavier than a gold atom is sometimes born — the top quark. It lives for tiny fractions of a second and decays, leaving a trace in the ATLAS detector. Physicists collected such traces for four years to understand how often the top quark and its mirror twin, the antiquark, appear.

A pebble drops into a pond, and ripples spread across the water. But sometimes the pebble doesn't sink right away: it skims beneath the surface, travels a few meters, and only then surfaces, creating ripples in an unexpected spot.

In the ATLAS detector at the Large Hadron Collider, protons collide billions of times per second. From this stream, physicists fished out eight events in which the collision produced two Z particles and one photon.

In the ATLAS detector at the Large Hadron Collider, particles leave tracks like skiers in the snow. Some tracks break off after a couple of centimeters: that's what a particle would look like if it were born, flew a little way, and then decayed into something invisible.

The tau lepton is a heavy cousin of the electron, living less than a trillionth of a second. It usually decays into lighter particles, but never directly into three muons: such a transition is forbidden by known laws of particle physics. If it did happen, it would mean unknown forces are at play.

At the Large Hadron Collider, protons collide at nearly the speed of light. Sometimes they don't smash apart but exchange photons — particles of light. These photons can produce a pair: one particle the detector sees, and another that flies off unnoticed.

Two particles flying apart in opposite directions behave as a single whole: measuring one instantly determines the state of the other. Such quantum entanglement has long been known for light particles, but now it has been observed for the first time in heavy Z bosons — the carriers of the weak force.

Cosmic rays are particles that arrive from deep space. When such a particle hits the atmosphere, it triggers a whole shower of new particles, like a billiard ball breaking a rack, sending balls scattering in all directions. To predict what such a shower will look like, we need to know how the primary particle interacts with the nuclei of air atoms.