High Energy Gluons in Events Containing a Quark-Antiquark Pair

Gluons are the particles responsible for holding the quarks together inside the proton, neutron and other hadrons.

Remember the diagram we used to represent qqg events:

A high energy gluon can be radiated from either the quark or the antiquark as shown in the following diagram:


Notice this diagram looks quite similar to that for the radiation of a photon from a quark, which we looked at in the previous section. Unlike a photon we do not observe the gluon directly in our detector. Instead the gluon produces a shower (or "jet") of particles, just like a quark, and it is this jet of particles we observe in our detector.

The presence of a gluon in addition to a quark-antiquark pair produces an event containing three jets: Here is an example event:

Example qqg Event Number 1

End-On View of Event


Side View of Event


If two high energy gluons are radiated then we may see events with four jets: qqg.

Notice that such events can start to look very much like the WW (four quark) events we looked at in an earlier section! Sometimes it is impossible to say if a particular event belongs to one type or the other.

(next event) Next take a look at some example "four fermion" events.

(challenge) Back to general section on "How to Identify Some Slightly More Complicated Types of Event".

(home) Back to Home Page with table of contents.

Terry Wyatt. March 1997.