Main Question or Discussion Point
I read some notes answering a question about how a Z boson is made in a proton anti-proton collision and it said that the quark antiquark collision is a very rare event because the antiquark has a small parton distribution function. Surely the up anti up(or down antidown) parton distributions are the same? The general context is the discovery of the W+ W- and Z bosons. Were these all quite difficult processes to observe?