High Energy Photons in Events Containing a Particle-Antiparticle Pair

Photons are particles of electromagnetic radiation. They do not carry any electric charge and therefore do not produce a track in the central part of our detector. However, they do carry energy. The energy of a photon is completely absorbed by the electromagnetic calorimeter. (Therefore, no energy is seen in the hadronic calorimeter.)

Here is an example event containing a high energy photon:

We can represent such an event by means of simple diagrams.
The first diagram shows a photon being radiated one of the outgoing muons: The second diagram shows a photon being radiated one of the incoming electrons:

We will refer to such events as: \(e^{+}e^{-} \rightarrow l^{+}l^{-}\gamma\)

Here is an example quark-antiquark event containing a high energy photon, which we represent by the following diagrams:

We will refer to such events as: \(e^{+}e^{-} \rightarrow q\bar{q}\gamma\)

• Next: Take a look at some high energy gluons in events containing a quark-antiquark pair.
• Back: "How to Identify Some Slightly More Complicated Types of Event"