A positively charged pion is a
meson that is made up of an up quark and a down antiquark. What is the baryon number of a
positively charged pion?
Alright, so let’s say this is our
pion. It’s made of an up quark and a down
antiquark. And we see that we represent it
with this symbol 𝜋 with a plus sign in the superscript. We want to know the baryon number
of this pion. And to figure that out, we can
recall first that any quark has a baryon number of positive one-third, while any
antiquark has a baryon number of negative one-third. So to get the total baryon number
of our pion, we’ll add together the baryon numbers of the particles that make it up,
in this case an up quark and a down antiquark.
The up quark has a baryon number of
positive one-third. And we add that to the baryon
number of the down antiquark, negative one-third, which we see gives a sum of
zero. This then is the baryon number of a
Another way we could recognize this
to be true is to note that since a pion is a meson, that is, a particle made of one
quark and one antiquark, it will have a baryon number of zero because that’s true
for all mesons. For all of these particles, we add
a baryon number of positive one-third for the quark to a baryon number of negative
one-third for the antiquark and get zero.