Background events

If protons collide, all sorts of particles can be created, not only Z or Higgs bosons! For example a W boson or a top quark can pop-up instead or in addition. These particles also decay immediately after their production, since they are as the Z and Higgs bosons, very heavy.

Collisions can also often lead to showers, or so-called “jets” of particles, without Z, W or top. Events with W, top or jets, which could look like a “signal” event, containing the particle you are searching for (Z, Higgs or others), are referred to as background events.

The cartoon drawing shows how a W- boson can be produced and decay.

Here the W- boson is produced in a collision between a gluon (g) and a down quark (d) and decays to en electron and an anti-neutrino. This is not the only way a W- boson can be produced and decay, there are many more!

You can compare the decay-products to those of the Z boson, for example. Remember: The Z boson was neutral, and therefore the sum of the charge of the decay-products had to equal 0. However, the W boson is not neutral, it has charge +/- 1. Therefore, the decay-products cannot be a particle-anti-particle pair of charged particles.