The diagram shows six baryons in
their quark content. The colors of the quarks correspond
to their color charge. Which baryons have color
configurations that are not possible?
Looking at these six baryons, we
see that they’re all made up of three quarks, as baryons must be. We’re told that the colors the
quarks take on, and we see that some are red, some are green, and some are blue
correspond to the color charge of the quarks. This means that in the diagram a
quark colored red, for example, this one, doesn’t indicate that that quark has a
positive electrical charge, but instead tells us that the color charge of that quark
is red. Along with this, we know that for
any color charge, whether red or green or blue, that doesn’t mean the particle with
that color charge actually has that color. Rather, this is just a convenient
way of talking about how a particle can have one of three kinds of charge.
This means that all of the
red-colored quarks we see in these diagrams have a red-color charge, all the green
ones have a green-color charge, and so on. In general, any of the six kinds of
quark, up, down, charm, strange, and top, bottom, can possess any of the color
charges. But, and this is important,
whenever we group quarks together to form particles called hadrons, the total or
overall color charge of these composite particles must be neutral. This is also called white.
From our knowledge of the primary
colors, we know that if we add together red and blue and green, then that gives us
the color white. And so, based on the rule that all
hadrons must be colorless or must have a total color charge of white, we can say
that for any baryon which is a particle made up of exactly three quarks, in order
for the total color charge of that Baryon to be colorless or white, it’s necessary
that one of the three quarks have a color charge of red, one have a color charge of
blue, and the last one have a color charge of green. This is the only way that the total
color charge of three quarks can add up to white.
And so, when our question asks
which baryons have color configurations that are not possible, we’re looking for
those configurations where we don’t have one red, one blue, and one green color
charge. We see two examples of that. The fourth baryon shown has two
blue color charges and no red, and the fifth one has two red, but no green. These baryons then will not have an
overall color charge of white and therefore are not possible color
configurations. All the other baryons do have one
green, one blue, and one red color charge and therefore are allowed.