Question Video: Determining the Baryon Number of a 𝜋 Meson Physics

Video Transcript

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 pion.

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.