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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.
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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. • It used to be thought that protons, neutrons and electrons were the fundamental particles of matter.
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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.
Quarks • There are three main quarks, up, down, and strange (for the exam). • They have corresponding antiquarks. • There are three others with even odder names, top,bottomand charm (not in exam).
Quark Properties • Quarks are the fundamental particles from which hadrons are made. • They cannot exist on their own. • Notice how they go in matching pairs.
Quark Numbers There 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. Eachantiquarkhas equal and opposite values of charge, baryon number and strangeness.
Quark Properties • Baryons 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 Combinations • Notice how you have these three options only:- • Baryon: • Anti-Baryon • Meson:
Question • Some 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)