What’s in a name?

Since I’m talking about the Large Hadron Collider, I should tell you what a hadron is. Put simply, it’s something that feels the strong nuclear force.  Clear?  Probably not, so let ‘s explain.

In the nucleus of an atom, there are protons and neutrons. The protons carry a positive electric charge, but the neutrons are neutral. Now, positive charges repel other positive charges and attract negative charges, so you would expect all the protons in the nucleus to repel each other, while the neutrons would just sit there happily.  So why then doesn’t the nucleus of an atom fly apart – what holds it in place?  It’s not gravitational attraction – that is far too weak to overcome the repulsion from the electrical charges.

The answer is that there is another force at work in the nucleus, that is an attractive force, and is stronger than the electrostatic force. Physicists call it the ‘strong nuclear force’. (There is also yet another, weaker force in the nucleus, which is given the name  ‘weak nuclear force’ – physicists are just soooo good at thinking of names for things –  but we won’t go along that road today.)  Both protons and neutrons feel the strong nuclear force, and this is what holds the nucleus together.

A ‘hadron’ is then a generic term for any particle that feels the strong nuclear force; both protons and neutrons are examples of hadrons. There are many more exotic particles that are hadrons, but they only tend to appear in particle accelerators or occasionally as a result of high energy cosmic rays hitting the atomosphere (a kind of ‘natural’ particle accelerator).

And there you have it. The Large Hadron Collider is simply a large machine that collides hadrons (mostly protons). As I said earlier, physicists are unusually creative when it comes to thinking up names for things. Or maybe not.

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