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Back before we knew about antimatter we just called everything matter. Ignoring CP-violation for a moment, there is nothing special about matter versus antimatter.

Once we knew about antimatter it was easily to label all of the common particles as matter. How do we do it for some of the more exotic stuff though?

For the Muon and Tau, do we call the matter version matter simply because they have negative charges like the electron? Do we use conservation of lepton number?

For things like the Top quark, how can we distinguish between the two and determine which is the Top and the other the Anti-Top? Did we decide that the matter one was the one with the positive charge because the Up quark has a positive charge?

How about for the W+ versus W- bosons? Does it matter which is the matter W and which is the antimatter W? Have we designated which a matter W?

For Neutrinos it seems extra tricky. Did we go based only on lepton number preservation?

For Mesons which have a quark and a different anti-quark, is the choice of the matter versus antimatter meson completely arbitrary?

Brandon Enright
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It started with conservation of quantum numbers, from baryon number when we did not know about quarks, to lepton number, when we discovered the positron.For the neutrino momentum and energy conservation played a role too, since it is only seen as a missing mass.

In time the symmetries in the assignments of the quantum numbers became more and more evident leading to the decouplet in the eightfold way. Bosons are their own antiparticles: photons, weak mesons and gluons ( and gravitons if they exist).

All the data we have is in agreement with these assignments. One decides whether it is a particle that was produced or an antiparticle from the results of the interaction, i.e. a study/fit-of-a-hypothesis of the quantum numbers carried off by the products of the interaction.

addition after reading comments:

We start by calling particles those that compose the ordinary matter that composes us. We are composed by atoms. The atoms are composed by protons neutrons and electrons. Those are "particles" by logical definition.

The neutron decays to: a proton , an electron and an electron-antineutrino . The identification of the neutrinos as particles and the neutral particle coming from the neutron decay as antiparticle starts from this reaction.

And of course the whole thing was consistent within the symmetries of the quark model as it first appeared on the scene.

W+ is the antiparticle of W- and W- the antiparticle of W+ but it is a moot point since it is just charge conservation that decides the decays. The muon decays to an electron and follows the identification as particle and for lepton number conservation by a nu_mu and antinu_e.

anna v
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an interesting question, no doubts. Indeed most of the time we rely on conservation of quantum numbers but there is an underlying structure to this. In principle changing a particle with an antiparticle amounts to a CP transformation. This is a symmetry for electromagnetic and (supposedly) strong interactions. Because of this, it doesn't really matter what we choose to call "matter" and what we choose to call "antimatter" (as long as we keep the conventions) when dealing with electromagnetism and strong interaction. The situation changes dramatically when weak interactions come to play a role. They violate CP "symmetry" either in a strong way or in an "indirect way". Never mind the way, the basic idea is that weak interactions can physically make the distinction between matter and anti-matter so this distinction is not anymore a matter of convention. Moreover, the current status of understanding would allow CP violation in strong interactions too (several terms can break CP symmetry in QCD) but none appears to be physically realized. Why? Also if one assumes that the current understanding is correct and CPT symmetry (which amounts to Lorentz covariance in the case of flat space-time) should be a true symmetry of nature then T symmetry must also be broken.

user33923
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