What is an "event"?
When a proton from the Tevatron hits an antiproton from the Tevatron, we call that an event
As the particles from the collision travel through the detector,
they (or most of them) interact with the detection equipment.
Physicists write computer programs that translate these "hits"
into a schematic called an event display
The schematic on the left represents the detector as if you were looking at
it from inside the beam pipe
. Each of the lines you see is the path of
a charged particle that was produced inside the detector.
What is a track?
Some parts of the detector at CDF are able to "see" a charged particle at several
points along its trajectory. Physicists write computer
programs that will turn these disparate hits into a full trajectory, or track,
for each particle.
Two ways to view an event display that illustrates the energies collected
by the CDF calorimeters. In the top image, energies are recorded
based on their angle to the beam pipe (which runs along the line marked "0").
The bottom diagram shows the energies relative to a plane perpendicular to the beam pipe, as if you were
staring straight into the beam.
Other parts of the detector determine the total energy of the electrons, photons, and hadrons
that hit them. Instead of a track, the results from these detectors are displayed as a bar graph, where a
larger bar corresponds to particles with higher energy. An event display for
the calorimeters, for example, could look something like the images on the right.
The pink bars in both diagrams correspond to energy collected by the electromagnetic calorimeters, the blue
to energy collected by the hadronic calorimeters.
Notice that particles that leave very straight tracks tend to correspond
to areas of high energy. This is because charged particles with greater energies
do not react as greatly to the magnetic field
set up within the detector. (For more information, read about momentum
With eight million events happening each second, you might wonder how physicists
keep the particles produced by one collision separate from the particles produced
by the next. Each part of the detector is designed to transmit a "hit" to
computers as quickly as possible.
Now you're ready to visit the first part of the detector. You may find it useful to
return to this page when you have completed the tour.