A collision at the LHC creates new particles, and within a few billionths of a second, most are gone. They are far too small and far too short-lived for any camera or microscope. So how did anyone ever find a new particle? Nobody has ever seen one. What physicists saw was what each particle left behind.
At the point where the LHC's beams cross, the newly made particles spray outward in every direction. Physicists wrap that point in layers of instruments, like the layers of an onion.
As a particle flies outward through the layers, it leaves a record. One part of the record is the path the particle traced: its track. The other part is the energy the particle dumped into the layers.
No layer photographs the particle itself. Each kind of particle leaves its own pattern of tracks and energy. So physicists identify each particle from what it leaves behind.
That answers the opening question. The Higgs boson was never seen. Physicists identified it from what appeared in the detector's layers.
A new particle flies out of a collision. What two records does the detector keep of it?
The detector's layers record the particle's track: the path it traced.
The layers also record the energy the particle dumped into them.
The detector records the particle's track and its energy.
Two different kinds of particle fly through the same detector. How do physicists tell which was which?
Each kind of particle leaves its own pattern of tracks and energy in the layers.
Physicists compare each recorded pattern with the pattern that kind of particle is known to leave.
They identify each particle from what it left behind: its own track-and-energy pattern.
At a collider, layered instruments record each particle that flies through them. What do they record?
Where do a detector's layers sit?
Layers of instruments wrapped around a collision point record what flies out. What is this package called?
A particle flies outward through a detector's layers and is gone. Which record do the physicists get of it?
Detector layers wrap all the way around the collision point instead of sitting on one side. Why?
A physicist wants to study the particles from one collision an hour after it happened. What does she examine?