9.2.E - Particle Physics. Year 12 Physics 9.8 Quanta to Quarks

Transcription

1 + 9.2.E - Particle Physics Year 12 Physics 9.8 Quanta to Quarks

2 + Atomic Size n While an atom is tiny, the nucleus is ten thousand times smaller than the atom and the quarks and electrons are at least ten thousand times smaller than that n We don't know exactly how small quarks and electrons are; they are definitely smaller than meters, and they might literally be points

3 + Standard Model of Matter

4 + Bosons n Have whole number integer spin

5 + Hadrons n Mediated by the strong nuclear force

6 + Fermions n Have half-integer spin

7 + Fundamental Forces n What holds it together? n The universe exists because the fundamental particles interact. These interactions include attractive and repulsive forces, decay, and annihilation. n There are four fundamental interactions between particles and all forces in the world can be attributed to these four interactions!

8 + Fundamental Forces Force Range (m) Rela/ve Strength Examples of Effects Strong Nuclear Electromagne:c Infinite 10-2 Weak Nuclear Binds protons and neutrons together Binds charged par:cles, atoms and molecules together Interacts with nuclear par:cles to change them into other par:cles Gravita:onal Infinite Draws masses together

9 + Gauge Bosons n Elementary particles responsible for the four fundamental forces n W and Z bosons - weak nuclear force Photons electromagnetic force Gluons strong nuclear force Graviton force of gravity n Photons, gluons and the graviton are massless but W and Z bosons have mass n Higgs boson is not a gauge boson but intermediates mass interactions

10 + Bosons Boson Force responsible for What it does Photon Electromagne:c force Binds charged par:cles, atoms and molecules together; acts over long distances; includes electrosta:c and magne:c forces. W and Z bosons Weak nuclear force Interacts with nuclear par:cles to change them into other par:cles; acts over about m. Gluon Strong nuclear force Binds quarks together in hadrons, binds neutrons and protons together to form nuclei; acts over m. Graviton Gravity Draws masses together, acts over very long distances (these par:cles have not been discovered yet).

11 + Mesons n Composite particles composed of one quark and one antiquark n Mediated by strong and weak forces n Very short half-lives and decay almost immediately in high energy interactions in cosmic ray interactions or particle accelerators n Examples include pions and kaons

12 + Baryons n Composite particles made up of three quarks n Mediated by the strong nuclear force n Proton = two up and one down quark n Neutron = one up and two down quarks

13 + Baryons n Hadrons are made up of quarks so that they have a net integer charge n Baryons are hadrons that are made of three quarks (qqq), e.g. protons and neutrons n Hadrons have much more mass than their constituent quarks. Why?

14 + Quarks n There are six quarks, but physicists usually talk about them in terms of three pairs: up/down, charm/strange, and top/bottom n Quarks have a fractional electric charge n Quarks have flavours: up/ down, charm/strange, and top/bottom

15 + Leptons n Elementary particles involved in radioactive decay n Mediated by the weak nuclear force n Includes electrons, neutrinos and muons

16 + Leptons n n n n There are six leptons, three of which have electrical charge and three of which do not. The best known lepton is the electron (e - ). The other two charged leptons are the muon (μ) and the tau (τ), which are charged but have a lot more mass than electrons. The other leptons are the three types of neutrinos (ν). They have no electrical charge, very little mass, and they are very hard to find. Quarks are sociable, whereas leptons are solitary particles. Think of the charged leptons as independent cats with associated neutrino fleas, which are very hard to see.

17 + Lepton Decay n The heavier leptons, the muon and the tau, are not found in ordinary matter at all. When they are produced they very quickly decay, or transform, into lighter leptons. n Tau leptons can decay into a quark, an antiquark and a tau neutrino. n Electrons and the three kinds of neutrinos are stable and thus the types we commonly see around us. n When a heavy lepton decays, one of the particles it decays into is always its corresponding neutrino. The other quark and its antiquark, or another lepton and its antineutrino.

18 + Fermions

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