Video: Recalling the Baryon Number of a Proton

What is the baryon number of a proton?


Video Transcript

What is the baryon number of a proton?

Before we calculate this, let’s talk about what a baryon is in the first place. Here’s how we can write out what that is. A baryon is a subatomic particle that’s made up of an odd number of quarks. To understand this definition though, we need to know what a quark is. So let’s talk about that too.

A quark is another type of subatomic particle that’s identified by the fact that it carries a fractional electric charge. That means that we wouldn’t write the charge of a quark in terms of an integer multiple of the charge of an electron.

Instead of being an integer multiple of that charge, it’s some fraction of it. It’s helpful to be talking about quarks because actually quarks are related to protons.

Protons as well as neutrons are actually not fundamental or elementary particles. Instead, they’re made up of other particles smaller than themselves. The ingredients, so to speak, that go into making a proton are three quarks: two of one type and one of another.

Speaking of the number of quarks in a particle, this relates to baryon number. The baryon number, we can write it as 𝐿 sub 𝐵 of a subatomic particle, is equal to one-third times the number of quarks in that particle minus the number of antiquarks. Quarks and antiquarks, by the way, are essentially mirror images, one of another.

Whatever their properties are in terms of charge or spin or other quantum numbers, they have the same magnitude but the opposite sign, much like the charge of an electron and a proton, same magnitude but opposite sign.

When we solve for the baryon number of a proton in particular, we know that the number of quarks in a proton is three. And the number of antiquarks in a proton is zero. The baryon number of a proton then is one-third times the quantity three minus zero. This simplifies to positive one.

That’s the baryon number. That is, one-third times the number of quarks minus the number of antiquarks of a proton.

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