Particle classification for SQA Higher Physics
This page covers the following topics:
3. Strange particles
4. Quarks and antiquarks
Hadrons are the heaviest particle known and is made up of smaller particles called quarks. Hadrons come in two categories: baryons and mesons. Baryons are hadrons made up of three quarks, including neutrons and protons. The only stable hadron is the proton, and all other hadrons will eventually decay into one. All baryons have a baryon number of 1, whereas all other particles have a baryon number of 0. Mesons are hadrons made up of 2 quarks, a quark and an antiquark. Mesons will never decay into protons. Antihadrons are made up of the antiquarks of the quarks that the corresponding hadron is made of.
Leptons are a family of fundamental particles, meaning that they are not made up of any other particles. Leptons are the lightest particles that exist. All leptons have a corresponding neutrino lepton, and the neutrino of the corresponding particle will be involved in reactions of the particle. The most common leptons are electrons, muons, tauons, electron neutrinos, muon neutrinos and tauon neutrinos, and their antiparticles. Neutrinos are chargeless particles with negligible mass, which makes them almost impossible to detect. Leptons do not interact with the strong nuclear force, but instead with the weak gravitational or electromagnetic interactions. The lepton number is the number of leptons in an interaction, where leptons have a lepton number of 1, antileptons have a lepton number of −1 and all other particles have a lepton number of 0. The lepton number is conserved in particle equations.
Strange particles are ones made up of strange or antistrange quarks. They are produced through the strong interaction and decay through the weak interaction. Strangeness is a number conserved in all interactions, except weak interactions, meaning that strange particles are always produced in pairs. Particles with a strange quark have strangeness −1, ones with an antistrange quark have strangeness +1 and ones with no strange quark have strangeness 0.
Quarks and antiquarks are the fundamental particles which make up hadrons. There are 6 types of quarks and their corresponding antiquarks: up, down, charm, strange, top, bottom. All quarks have a baryon number of 1/3. All quarks also have strangeness of 0, except for the strange quark, which has strangeness −1. Protons and neutrons are both made up of quarks: a proton is made of two up quarks and one down quark (uud) and a neutron is made of one up quark and two down quarks (udd).
State what quarks are.
Quarks are the fundamental particles which make up hadrons.
State the quark combination of an antiproton.
A proton's quark combination is uud.
An antiproton will be made up of the antiquarks of a proton.
So, the quark combination of an antiproton is ūūđ.
An omega particle is made up of three strange quarks. Calculate the charge, the baryon number and the strangeness of the particle.
Charge = − 1/3 − 1/3 − 1/3 = −1.
Baryon number = 1/3 + 1/3 + 1/3 = 1.
Strangeness = − 1 − 1 − 1 = −3.
Define what leptons are.
Leptons are a family of fundamental particles, meaning that they are not made up of any other particles.
Explain what baryons are.
Baryons are hadrons made up of three quarks.
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