Event Display Pictures : Typical Hadronic Events
Most often at Z resonance, the final state particles we see in the detector are two or more jets of hadrons.
The electron and a quark-antiquark pair (
)
annihilate to produce the Z, which decays to produce a quark and an
anti-quark flying apart. Quarks and antiquarks interact through the
strong force field. As they separate, the region of strong force-field
between them has enough energy-density to produce additional quark plus
anti-quark pairs. (Recall Einstein's relation: E = mc2).
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"Click" on the an image below. The image will open into
a new browser Two views of the same event |
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Event 10507_346_700_z |
 Event 10507_346_700_x |
 Event 11173_22_600_z |
 Event 11173_22_1200_3 |
The collection of quarks and antiquarks are arranged by strong-force fields into color neutral hadrons, which is what is detected. The process all occurs within a region about the size of a single proton, so it is extremely fast and cannot be observed.
In this process, called hadronization, about 15 new particles (mesons or baryons) are eventually created from each quark. Because of the high momentum of the initiating quarks, the new particles tend to bunch up in jets. So, typically, two jets are created, one containing the original quark (plus many more quarks and anti-quarks) all moving roughly in the direction that quark was going, and an opposite moving group (or jet) of particles containing the original antiquark.
Of these new particles, the charged ones leave tracks in the vertex detector and drift chamber. They form showers in the calorimeter as well.
The neutral particles have no electromagnetic interactions and, hence, pass undetected right through the vertex detector and drift chamber. They usually make it all the way to the second layer of the calorimeter before showering and stopping. The existence of events of this type allows physicists to study the properties of the many other types of particles that are created in the hadronization process.
In the pictures above, notice the mess of green tracks forming two jets in the tracking chambers and the widely spread bunches of energy in the calorimeters. Some of the calorimeter energy doesn't "match" the trajectory from the charged tracks and is assigned to the neutral hadrons. Can you find evidence of these "unmatched" energy deposits in the calorimeter?