Hadrons

Hadrons are made of quarks

There are two types of hadron that we have to know about at A Level:- the baryon and meson.

• Baryon - 3 quarks - baryon number of 1- proton and neutron
• Anti-baryon - 3 anti-quarks - baryon number of -1 - antiproton and antineutron.
• Meson - a quark and an anti-quark - baryon number 0 ('cos its not a baryon!) - kaon, pion

You only need to learn about three quarks - the up 'u', down 'd' and strange 's' but there are others. You don't need to worry about them for the AQA course, but it would be a good idea to look them up and give yourself a more complete picture.

The examiner could give you baryons that contain other quarks and expect you to classify them - if they did that they would have to give you the quark properties in a table.... but you are expected to recall the general types of particle classification shown above!

Each quark has characteristics that are listed on your data sheet - you do NOT have to learn these, you should be able to use them to work things out!

• The only two types of meson you need to know about are the pion π and the kaon κ.
• The kaon involves 'strangeness'. It is the only strange particle you have to deal with in this course.
• The pion has no strange quark.
• After the symbol comes a charge sign - which you can work out from the data book.

As we are limited to u, d and s (and I have already told you that the only hadron we have to deal with that has a strange quark is the kaon) we only have to concern ourselves with two baryons: the proton and the neutron.
 

You know that a neutron is neutral and a proton has a charge of +1.

Using the information in the table above (charge!) deduce what arrangement of 'u' and 'd' (three in total) makes each of the baryons we have to know about.

proton quark composition: ?

neutron quark composition: ?

• The only two types of baryon you need to know about are: the proton 'p' and the neutron 'n'.
• Neither is 'strange'. (The kaon (a meson) is the only strange particle you have to deal with in this course). They are both made up of only 'u' and 'd'.
• They are each composed of three quarks.
• You know their charge so you can work out their composition from the data book.

What do hadrons do?

Mesons are involved in the strong force - they help to hold the nucleus together.

Baryons are particles that participate in strong interactions They are composed of three quarks, and are therefore generally more massive than mesons..

See pion and kaon