# Lepton Number

What do we mean by lepton number and why is it useful?

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Up Learn – A Level physics (aqa)

## The Atom and Beyond

So far, we’ve seen three quarks.

And, we’ve seen the names, symbols and charges of these quarks.

Next, there are two more properties that we need to look at.

The first of these is baryon number.

And, to find out what that is… we need to start by looking at what a baryon is.

For instance, a proton is made up of three quarks… so it is a baryon.

Next… a neutron is also made up of three quarks… so, it is also a baryon.

When a particle is made up of three quarks… we call it a baryon.

Next, a baryon has a property called a baryon number.

Where all baryons have a baryon number of plus one

For example, a proton has a baryon number of plus one.

And so, a neutron has a baryon number of…

A neutron has a baryon number of plus one.

And we know that because…

A neutron is a baryon since it’s made up of three quarks.

And, all baryons have a baryon number of +1.

Finally, why do we have baryon numbers? What’s the point of them?

Well, baryon numbers help us to understand what’s happening during particle interactions.

For instance, when we smash protons together at the Large Hadron Collider in Cern.

For now, we’re not going to look at these interactions.

And so we’re not going to look more at the baryon number … right now…

…but we will dive into the baryon number more in the particle interactions section of the course.

To sum up…

Baryon is the name we give for particles made up of three quarks.

A baryon has a baryon number of plus one.