* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download unit 5: particle physics
Introduction to quantum mechanics wikipedia , lookup
Canonical quantization wikipedia , lookup
Spin (physics) wikipedia , lookup
Symmetry in quantum mechanics wikipedia , lookup
Atomic nucleus wikipedia , lookup
History of quantum field theory wikipedia , lookup
Minimal Supersymmetric Standard Model wikipedia , lookup
Nuclear structure wikipedia , lookup
Electric charge wikipedia , lookup
Neutrino oscillation wikipedia , lookup
Feynman diagram wikipedia , lookup
Technicolor (physics) wikipedia , lookup
Renormalization wikipedia , lookup
Quantum electrodynamics wikipedia , lookup
Double-slit experiment wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
Future Circular Collider wikipedia , lookup
Weakly-interacting massive particles wikipedia , lookup
ALICE experiment wikipedia , lookup
Quantum chromodynamics wikipedia , lookup
Identical particles wikipedia , lookup
Compact Muon Solenoid wikipedia , lookup
ATLAS experiment wikipedia , lookup
Strangeness production wikipedia , lookup
Electron scattering wikipedia , lookup
Grand Unified Theory wikipedia , lookup
Mathematical formulation of the Standard Model wikipedia , lookup
The Structure of Matter The Standard Model of Elementary Particles: Particles and Antiparticles Composite Particles: Examples: In the 1950s and 1960s, hundreds of other particles were discovered, many of which are very unstable and so are not found in ordinary matter. Elementary Particles: particles not made out of any smaller component particles; 2 elementary particles of the same kind are completely identical. 3 Classes of Elementary Particles: a) b) c) Antiparticles – All antiparticles are denoted with a line above the symbol Examples: If a particle has zero electric charge, the antiparticle can still be distinguished because of other quantum numbers Example: Some particles are their own antiparticle and must be electrically neutral Example: Antimatter – What happens when antimatter comes into contact with matter? Which is predominant in today’s universe, matter or antimatter? Quantum numbers: Examples: Quarks Quarks: There is solid experimental evidence for the existence of 6 types or “flavours” of quarks Quark flavour Symbol Electric Charge (e) Rest Mass (MeV c-2) Spin (h/2π) Up Down Strange Charmed Bottom Top Note: A particle’s “spin” is a quantum property that is analogous to, but not actually, angular momentum (L=mvr). All known particles have spin, which must be either an integral or halfintegral multiple of the quantity h/(2π). Bosons: Fermions: So all quarks are…. Hadrons – Meson – Baryon – The proton is a baryon made out of…. The neutron is a baryon made out of…. 1. Show that the charge of a proton is 1. 2. Show that the charge of a neutron is 0. 3. What is the quark content and the charge of an antiproton? 4. What is the quark content and the charge of an antineutron? Baryon number (B): Baryons are assigned a quantum number What is the baryon number for: protons and neutrons? antiprotons and antineutrons? quarks? antiquarks? So how does B of an antiparticle compare to B of the particle? Law of Conservation of Baryon Number: Baryon number is conserved in ALL reactions. _ Example: n + p n + p + p + p 5. Show that the reaction below cannot occur; if it did, the law of conservation of baryon number would be violated. -- p + p π0 + π0 + n Leptons Leptons: the electron and its neutrino, the muon and its neutrino, and the tau and its neutrino, as well as all of their antiparticles There is solid experimental evidence for the existence of 6 types of leptons Lepton Symbol Electric Charge (e) Rest Mass (MeV c-2) Spin (h/2π) Electron Electron neutrino Muon Muon neutrino Tau Tau neutrino Because of their spin, all leptons are….. The leptons of each family or generation are assigned a lepton number. Since there are 3 families, there are 3 lepton numbers Lepton number (L): Type of Leptons and Lepton numbers: electron, muon, and tau lepton with numbers, Le, Lμ, and Lτ The 3 kinds of lepton number are individually conserved in all reactions as is the overall Lepton number. Le Electron, e Electron neutrino, νe Muon, μMuon neutrino, νμ Tau, τTau neutrino, ντ Lμ Lτ 6. Show that all lepton numbers are conserved in the following muon decay: _ μ e + νe + νμ - - 7. Do the following reactions conserve lepton number? a. p+ e+ + π0 b. π0 e+ + μ- _ c. τ π + ντ + + Exchange Particles Exchange Particles: associated with interactions or forces; includes the photon (γ), the W and Z bosons (W± and Z0), 8 particles called gluons, and the graviton. There is solid experimental evidence for the existence of all exchange particles except the graviton. Gauge bosons: particles that mediate (or transmit) the force between a pair of particles The 4 fundamental forces have different ranges and a different boson is responsible for each force. The mass of the boson establishes the range of the force. The bosons carry the force between particles. The Higgs Particle or Higgs boson: a boson-like force mediator, but does not actually mediate any force; explains the mass of other particles, including the W and Z bosons; not known if this particle is elementary; was tentatively confirmed in 2013 to be positively charged and to have zero spin. Leptons and quarks of the standard model can be arranged into 3 families or generations. 1st generation 2nd generation 3rd generation Leptons e- Quarks u νe d μ- s νμ c τ- b ντ T Conservation Laws In all reactions, the following quantities are always conserved: 1. 2. 3. 4. 5. 6. Strangeness (S): Strange quark has a strangeness of: Strange antiquark has a strangeness of: When is strangeness conserved? When strange particles are created in a strong interaction, but it is not conserved when they subsequently decay through the weak interaction. This is why strange particles are always produced in pairs. If 2 particles interact to produce a strange particle, then a strange antiparticle must also appear. In the following reactions, determine if Q, B, L, and S are conserved. _ _ 8. uud + ud ds + uds _ _ _ 9. ds ud + ud _ 10. uds ud + uud Interactions and exchange particles Basic interaction vertices: There are 4 fundamental forces or interactions in nature. Interaction Interaction acts on Exchange Particle(s) Relative Strength Electromagnetic Weak (nuclear) Strong (nuclear) Gravitational The electromagnetic and weak nuclear interactions have been combined to form the electroweak interaction. How does the range of the exchange force relate to the mass of the exchange particle? The shorter the range of the exchange force, the more massive the exchange particle. The exchange particles for gravitation and the EM interaction both have infinite range, so must have zero rest masses. Meanwhile the weak interaction has the heaviest boson because its range is the shortest. The strong interaction has an exchange particle of intermediate mass. At a fundamental level, particle physics views an interaction between 2 elementary particles in terms of interaction vertices. All interaction vertices should be read from left to right. The left hand side represents BEFORE and the right hand side represents AFTER. Usually the time axis goes to the right and the space or position axis goes upwards, but they can be reversed. Because arrows on antiparticles are drawn in the opposite direction to those on particles, we sometimes say that these antiparticles travel backwards in time. This is just an expression! All particles/antiparticles move forwards in time. The electromagnetic interaction is the exchange of a virtual photon between charged particles. The exchanged photon is not observable. This interaction vertex is show on the left below. By rotating the arms of the vertices, the following interaction possibilities are generated. Electric charge, baryon number, and lepton number are conserved at an interaction vertex. The total Q, B, and L, going into a vertex must equal the total Q, B, and L leaving the vertex. Feynman Diagrams Feynman diagrams: pictorial representations or “spacetime diagrams” of particle interactions that uses interaction vertices in order to build up possible physical processes. Examples: below left is electron-electron scattering (the exchange of a virtual photon in the interaction between electrons), below right is Higgs decay to two photons via top loop; In this Feynman diagram below, an electron and positron destroy each other, producing a virtual photon which becomes a quark-antiquark pair. Then one radiates a gluon. Other examples of Feynman diagrams for basic interaction vertices. To build a Feynman diagram,` the following are needed: 1) 2) 3) Examples: Draw the Feynman diagram for the following processes: 11. e- + e+ e- + e+ 12. e- + e+ γ + γ 13. beta minus decay in which a neutron decays into a proton, an electron, and a neutrino 14. positive beta (positron) decay: p n + e- + νe Quark Confinement (or confinement of colour): Why is this so? Suppose you wanted to remove a quark from inside a meson. The force between the quark and the antiquark is constant no matter what their separation is. Therefore, the total energy needed to separate the quark from the antiquark gets larger and larger as the separation increases. To free the quark completely would require an infinite amount of energy, and so it is impossible. If you insisted on providing more and more energy in the hope of isolating the quark, all that would happen would be the production of a meson-antimeson pair and not free quarks. Table of some baryons Particle Symbol Proton Neutron Delta Delta Delta Delta Lambda Sigma Sigma Sigma Xi Xi Omega p n Δ++ Δ+ Δ0 ΔΛ0 Σ+ Σ0 ΣΞ0 ΞΩ- Quark Content uud ddu uuu uud udd ddd uds uus uds dds uss dss sss Mass MeV/c2 938.3 939.6 1232 1232 1232 1232 1115.7 1189.4 1192.5 1197.4 1315 1321 1672 Mean lifetime (s) Stable 885.7±0.8 6×10-24 6×10-24 6×10-24 6×10-24 2.60×10-10 0.8×10-10 6×10-20 1.5×10-10 2.9×10-10 1.6×10-10 0.82×10-10 Decays to Unobserved p + e- + νe π+ + p π+ + n or π0 + p π0 + n or π- + p π- + n π- + p or πo + n π0 + p or π+ + n Λ0 + γ π- + n Λ0 + π0 Λ0 + πΛ0 + K- or Ξ0 + π- Table of some mesons Particle Symbol Charged Pion Neutral Pion Charged Kaon Neutral Kaon Eta Eta Prime π+ π0 K+ K0 η η' Antiparticle π− Self K− K0 Self Self Quark Content ud uu - dd ds uu + dd - 2ss uu + dd + ss Mass MeV/c2 139.6 135.0 493.7 497.7 547.8 957.6 Mean lifetime (s) 2.60×10-8 0.84×10-16 1.24×10-8 5×10-19 3×10-21 Principal decays μ+ + νμ 2γ μ+ + νμ or π+ + π0