How to Identify Events Containing a Pair of W Particles

The production of a W⁺W^- pair of particles can be represented by the following diagrams:

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After about 10^-25 seconds a W decays, so we don't see it directly in our detector. A W can decay in two different ways. The first type of decay produces a lepton and an antineutrino. For example, the following picture shows the W decaying to a muon and a muon antineutrino.

In a similar way a W can to decay to produce an electron or a tau lepton.

The second type of W decay produces a quark and an antiquark:

Because both the W⁺ and the W^- decay to produce particles we see in the detector, the resulting events are slightly more complicated than the particle-antiparticle pair events we looked at in the previous section. We get different types of W⁺W^- event depending on whether both W⁺ and W^- decay to produce quarks, both decay to produce leptons, or one W decays to produce quarks and one W decays to produce leptons.

Here are some examples of the different types of W⁺W^- events:

• both W⁺ and W^- decay to produce a quark and an antiquark:
  • example events
• both W⁺ and W^- decay to produce a charged lepton and a neutrino:
  • example events
• one W decays to produce a charged lepton and a neutrino, and the other W decays to producea quark and an antiquark:
  • example events
  • example events
  • example events

Once you've understood the way we identify the different types of W⁺W^- events, then please:
click here to proceed to the next part of the programme, which is "Challenge Part 3".

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