# Question Video: Identifying Mesons Physics • 9th Grade

Which of the particles shown in the diagram are mesons? The quarks shown in the diagram are colored according to their electric charge.

02:12

### Video Transcript

Which of the particles shown in the diagram are mesons? The quarks shown in the diagram are colored according to their electric charge.

Okay, we see these six particles marked (a), (b) (c), (d), (e), and (f). And we want to figure out which of them are mesons. We’re told that the quark shown in this diagram are colored according to their electric charge. Positively charged quarks, like the up quarks in particle (a), are colored red and negatively charged quarks, like the down quark here, are colored blue. Now mesons are a class of particle that are defined by two conditions. First, they’re made up of one quark and one antiquark. And second, the total relative charge of a meson is an integer value. Considering this first condition that mesons are made of one quark and one antiquark, we see right away that three of these particles don’t meet that condition.

Particles (a), (d), and (f) are all made of three quarks and therefore can’t be mesons, leaving us with particles (b), (c), and (e). Looking at these three, we see that each one is indeed made up of one quark and one antiquark. So all that remains to be seen is if each one has a total relative charge of an integer value. Looking first at particle (b), we can recall that an up quark has a relative electric charge of positive two-thirds, where this is positive two-thirds times the charge of a single proton, while a down antiquark has a relative electric charge of positive one-third. Two-thirds plus one-third equals one, which is an integer. So particle (b) satisfies both of our conditions and therefore is a meson.

Considering next particle (c), we know that a strange quark has a relative electric charge of negative one-third times the charge of a proton, while an up antiquark has a relative charge of negative two-thirds. Adding these two charges together, we find a result of negative one, which also is an integer. So particle (c) is a meson as well. The charm quark in particle (e) has a relative charge of positive two-thirds and the down antiquark has a relative charge of positive one-third. Combining these charges gives an overall charge of one. So this particle too is a meson. In this diagram then, particles (b), (c), and (e) are all mesons.