Particle physicists use the term cross section to describe the probability that two particles will collide and interact in a certain way. When proton beams cross in the Large Hadron Collider (LHC), many different processes can occur.
The cross section of a particular process depends on the type and energy of the colliding particles. Processes with larger cross sections occur more often than processes with small cross sections. At the LHC, certain particles such as W and Z bosons have large cross sections, so they will be observed more often. The production of a Higgs boson at the LHC has a much lower cross section, so is more difficult to produce.
Check out the cross section and luminosity cheat sheet to learn more.