# Quarks and Antiquarks

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Quarks and Antiquarks. Particle Physics Lesson 9. Particle Physics. Particle physics is concerned with fundamental particles , which means that the particles can't be broken down any further. - PowerPoint PPT Presentation

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• Quarks and AntiquarksParticle Physics Lesson 9

• Particle PhysicsParticle physics is concerned with fundamental particles, which means that the particles can't be broken down any further. It used to be thought that protons, neutrons and electrons were the fundamental particles of matter.

• VideoIn Search of Giants (5 of 15) The Standard Model of Particle Physics

• Hadrons are not fundamental!It has been found that nucleons (proton and neutron) are made up of smaller particles, so nucleons are now not fundamental.

Particle accelerators fired electrons at protons and showed there were three scattering centres.

• QuarksThere are three main quarks, up, down, and strange (for the exam). They have corresponding antiquarks.

There are three others with even odder names, top, bottom and charm (not in exam).

• Quark PropertiesQuarks are the fundamental particles from which hadrons are made.

They cannot exist on their own.

Notice how they go in matching pairs.

• Three Generations of Matter

• Quark NumbersThere are three quantum numbers associated with quarks: Charge, expressed as the fraction of the electronic charge. 1/3e = 5.33 10-20 C Baryon number Strangeness number, when there are strange quarks. Each antiquark has equal and opposite values of charge, baryon number and strangeness.

• Quark Numbers

QuarkCharge (Q)Baryon number (B)Strangeness (S)Down -1/31/30Anti-down+1/3-1/30Up+2/31/30Anti-up-2/3-1/30Strange-1/31/3-1Anti-strange+1/3-1/31

• Quark PropertiesBaryons are made of three quarks; antibaryons of three antiquarks. Mesons are made up of one quark and one antiquark. Mesons are not made up of two quarks.

Gluons bind quarks together; they are subject to the strong interaction.

Important Notes: Strangeness is conserved in strong interactions only (next lesson).

• Hadron Quark CombinationsNotice how you have these three options only:-Baryon:

Anti-Baryon

Meson:

• Meson Quark Combinations

• Complete the table for the following hadrons:

ParticleCompositionBaryon no.ChargeProton (p)uud1+1eAntiprotonNeutral Pion (0)Neutral Kaon (K0)Lambda (0)

• Complete the table for the following hadrons:

ParticleCompositionBaryon no.ChargeProton (p)uud1+1eAntiproton-1-1eNeutral Pion (0)u or d00Neutral Kaon (K0)d or s00Lambda (0)uds10

• Beta decay

• QuestionSome mesons such as the neutral Kaon and the neutral Pion (Pi-meson) can be made up in different ways.

Why does a meson always have a baryon number of 0? It is made up of a quark and an antiquark (P) The baryon numbers add up to zero (P)

• discovery of the ++c baryon

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