A Xi baryon is a particle that is
made up of one up quark and two strange quarks. What is the baryon number of a Xi
Okay, so let’s say that this here
is our Xi baryon with its one up quark and its two strange quarks. We want to figure out what is the
baryon number of a Xi baryon. One way to start doing this is to
recall that baryon number is a basic property of particles. In that way, it’s like electric
charge or mass. In the case of electric charge, for
example, we know that a particle is given a charge based on how many positive and
negative fundamental charges it possesses. Baryon number though, rather than
being determined by the number of protons and electrons, is determined by the number
of quarks and antiquarks in a particle.
A quark has a baryon number of
positive one-third, while an antiquark has a baryon number of negative
one-third. So to figure out the baryon number
of a Xi baryon, we can add together the baryon number of its quarks. Each one has a baryon number of
positive one-third, and so they add up to one. This is indeed the baryon number of
a Xi baryon.
But note that there’s another way
that we could’ve gotten the same answer. We could recall that any particle
called a baryon has a baryon number of positive one. This is true because a baryon, by
definition, is a particle made up of three quarks. Either way we look at it, the
baryon number of this particle is positive one.