Anti-particles are often made out to be a lot more mystical and mysterious than they actually are, thanks to science fiction, and other fiction such as Dan Brown’s Angels and Demons. I emphasize, fiction.
Every type of particle has an anti-particle. Usually this is a distinct type of particle, but it can happen that the anti-particle and the particle are the same. Only particles satisfying certain conditions (for example, if they are electrically neutral) may be their own antiparticles. The only examples so far from the list of elementary particles are photons, Z particles, gluons and gravitons… and possibly the three neutrinos. Every other particle has a distinct anti-particle, with the same mass but opposite electric charge. [The neutron is an example of an electrically neutral particle that is not its own antiparticle; like the proton, the neutron contains more quarks than anti-quarks, whereas the anti-neutron contains more anti-quarks than quarks.]
For those particles that differ from their anti-particles, the names of the anti-particles are usually pretty obvious (up anti-quark, anti-neutrino, anti-tau) with the exception of the anti-electron, which is usually called the positron.
What made anti-matter so famous and thence so mysterious-sounding? The statement that “matter and anti-matter annihilate into pure energy.” This statement, though it sounds cool, is glib. It isn’t entirely false, but it certainly isn’t true either. The reality is both more complex and less astonishing-sounding. I’ll explain that elsewhere.
Often, to keep things simple and short, physicists drop the “anti” prefix when it is obvious from context. Here are two of many examples:
- Many processes produce a muon and an anti-muon; physicists will sometimes call this a “muon pair”.
- A W particle decaying to an up quark and a down anti-quark may be said to decay “to quarks”.
I mostly try to avoid such shorthand on this site, since it is confusing if you’re not used to it, but it does add to the verbiage. Other common shorthand used by particle physicists can be found here (soon).