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Particle physics - Standard Model
There are two types of elementary particles: fermions and bosons. Fermions obey the Pauli exclusion principle and have half-integer spin, while bosons do not obey PEP and have integer or zero spin. Fermions are further divided into leptons, which do not feel the strong force, and quarks, which do feel the strong force. Quarks combine to form composite particles called hadrons, which are divided into baryons containing three quarks and mesons containing two quarks. The four fundamental forces are electromagnetic, strong, weak, and gravity, and are mediated by gauge bosons.
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Overview of the field of study focusing on fundamental particles.
Definition of elementary particles as those with no internal structure.
Classification into three groups: Quarks, Leptons, and Gauge Bosons.
Fermions are elementary particles obeying Pauli's exclusion principle. They include quarks and leptons.
Overview of six lepton types, their antiparticles, and the lepton number conservation law.
Details on six quarks and their antiparticles. Explanation of how they form baryons and mesons.
Comparison between fermions (like leptons and quarks) and bosons (like gauge bosons).
Introduction to gauge bosons mediating fundamental forces with their properties.
Discussion on the theorized Higgs boson affecting particle mass and its significance in physics.
Classification based on quantum numbers including charge, spin, and baryon/lepton numbers.
Explanation of how this principle applies to fermions and its absence for bosons.
Definition of antiparticles and their properties, including charge and spin.
Classification based on quantum numbers including charge, spin, and baryon/lepton numbers.
Differentiation of fermions (non-integer spin) and bosons (integer spin) and spin states.
Classification based on quantum numbers including charge, spin, and baryon/lepton numbers.
Compilation of properties distinguishing fermions from bosons and definition of composite particles.
Introduction to the four fundamental interactions: electro-magnetic, strong, weak, and gravity.
Explanation of how particles are exchanged to mediate fundamental forces using Feynman diagrams.
Mechanics of virtual particles and the Heisenberg Uncertainty Principle affecting interactions.
The relationship between mass and range of interactions for virtual particles based on HUP.
Illustration of Feynman diagrams used to represent interactions and conservation laws in particle physics.
Exercises provided for applying knowledge of Feynman diagrams in particle interactions.
Set of review problems to assess understanding of discussed particle physics concepts.Further exploration of quark types, their combinations into baryons/mesons, and properties.
Differentiation of fermions (non-integer spin) and bosons (integer spin) and spin states.
Description of quarks' color charge, confinement, and the necessity of color neutrality in particles.
Introduction to Strangeness as a quantum number and its conservation in interactions.
Overview of conservation laws governing particle interactions: mass-energy, baryon, lepton numbers.
Description of beta decay process, including particle transformations and conservation of lepton number.
Compilation of properties distinguishing fermions from bosons and definition of composite particles.
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Particle physics - Standard Model
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- 2. Elementary Particle A particlewith no internal structure.
- 3. Three types ofelementary particles Quarks Leptons Exchange Particles (Gauge Bosons)
- 4. elementary Gauge Bosons particles that feel strong force FERMIONS – follow Pauli exclusion principle elementary particles DO NOT follow that do not Pauli exclusion feel strong principle force
- 5. FERMIONS Two types offundamental particles are classified as FERMIONS (they follow Pauli’s exclusion principle and have ½ spin numbers) Present theory states that these particles cannot be broken down into even “smaller” particles. These two classes of fundamental particles are. Leptons – do not feel the strong force Quarks – feel the strong force
- 6. Leptons There are sixtypes of lepton and each has an antiparticle (opposite charge). Family -1 charge zero charge 1 electron (e) electron-neutrino ( e) 2 muon ( ) muon-neutrino ( ) 3 tau ( ) tau-neutrino ( ) Each lepton has a designated lepton number of +1. The antiparticles of each lepton are -1. For any interaction, the sum of all the lepton numbers must remain constant. This is the lepton number conservation law.
- 7. Quarks (isolated quarkshave never been detected) There are six types of quarks and consequently six types of anti-quarks (with opposite charge). Family +2/3 charge -1/3 charge 1 up (u) down (d) 2 charm (c) strange (s) 3 top (t) bottom (b) Quarks and anti-quarks combine to form composite particles called HADRONS: two families of hadrons 3 quarks = baryon (ex. protons and neutrons) 2 quarks = meson (ex. pions)
- 8. Fermions Bosons elementary particles elementary particles gauge bosons HADRONS composite particles composite particles baryons mesons (made of 3 quarks) (one quark + one anti quark)
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- 10. Exchange Particles –Mediate Fundamental Forces gauge bosons graviton gluon (gravity) (strong) photon w+, w -, z0 (electromagnetic) (weak) electroweak Range: gravity, electromagnetic >> strong > weak Strength: strong > electromagnetic >> weak >> gravity Mass: weak >>>> strong, gravity, electromagnetic
- 11. The Higgs Boson Notdiscovered yet, only theorized An exchange particle that gains mass when it interacts with other particles. The existence of Higgs is important because it is fundamental to theories about how particles have mass. If it doesn’t exist, much of the current theory will need to be revised.
- 12. Classifying Particles Thereare many different properties used to classify a particle. These intrinsic properties are expressed as quantum numbers. Quantum numbers tell us about -electric charge - spin - strangeness -.charm - color (not actual color) - lepton number - baryon number
- 13. Pauli’s Exclusion Principle Notwo particles in a closed system (such as an atom) can have the same set of quantum numbers. All fermions follow the PEP Bosons do not follow the PEP
- 15. Quantum Number –electrical charge Fundamental particles can have positive, negative or no charge. An ANTIPARTICLE has the identical mass to a particle but opposite charge (if charged) and opposite spin (if there is spin).
- 16. Classifying Particles Thereare many different properties used to classify a particle. These intrinsic properties are expressed as quantum numbers. Quantum numbers tell us about -electric charge - spin - strangeness -.charm - color (not actual color) - lepton number - baryon number
- 17. Quantum Number -SPIN All fermions have non-integer spin example electrons +½ (or – ½ ) All bosons have integer (or zero) spin
- 18. Classifying Particles Thereare many different properties used to classify a particle. These intrinsic properties are expressed as quantum numbers. Quantum numbers tell us about -electric charge - spin - strangeness -.charm - color (not actual color) - lepton number - baryon number
- 19. Particles - Summary All observed particles fermions bosons ½ integral spin zero or integral spin obey Pauli exclusion do not obey Pauli exclusion mesons gauge leptons quarks (2 quarks) bosons Hadrons baryons (3 quarks)
- 20. Fundamental Interactions The fourfundamental interactions of nature are: electromagnetic, strong, weak, and gravity The electromagnetic and the weak interactions are two aspects of the same interaction, the electroweak interaction
- 21. Mediation of FundamentalForces The fundamental forces are mediated by the exchange of particles. These particles are called exchange bosons. A Feynman diagram can be used to show how interactions between particles are mediated by bosons. The electromagnetic force is mediated by photons. These photons are unobservable and are termed virtual photons to distinguish them from real ones.
- 22. Exchange Particles :the nature of force All four of the fundamental forces involve the continuous exchange of “virtual” particles The creation of “virtual” particles is a breach of conservation laws (as they are created from nothing) so they can only exist for a short period of time. The maximum range of an exchange force is dictated by the Heisenberg uncertainty principle.
- 23. The Heisenberg UncertaintyPrinciple (HUP) It is impossible to make precise measurements of both the position and momentum (velocity) of electrons or any other particles. The very act of measuring changes these quantities. The more precise one measurement is, the less precise the other one becomes. .
- 24. Implications of theUncertainty Principle HUP can be applied to the h relationship between energy E t and time. 4 Here, the uncertainty principle implies that the life time of a virtual particle is inversely proportional to its mass (energy) The more massive the exchange particle, the shorter its life. Why is the range of the strong and weak nuclear force very small compared to the infinite range of the electromagnetic and gravitational force?
- 25. The uncertainty inthe energy of a virtual photon is 7.1 × 10-19 J. Determine the uncertainty in the time for the electromagnetic interaction between two electrons exchanging the virtual photon. . 34 h 6.6 10 17 t 19 7.4 10 s 4 E 4 (7.1 10 )
- 26. Range of Interactionsof Exchange Particles. The range of a virtual particle (and hence the force it mediates) is governed by the equation below (from HUP) h h is Planck’s constant R c is the speed of light m is the REST MASS of the virtual particle 4 mc We see here again that range is inversely proportional to the rest mass
- 27. The strong forcehas a range of about 10-15 m. Calculate the rest mass of the related exchange particle. What type of particle is this? 34 h 6.6 10 28 R 15 8 2 10 kg 4 mc 4 (10 )(3.0 10 ) this is a gluon
- 28. FEYNMAN DIAGRAMS Exchange forcesare often pictured with Feynman diagrams. At each vertex in a Feynman diagram, conservation laws such as charge, lepton number and baryon number must be obeyed
- 29. Different lines aredrawn for different particles. There are some variations in the conventions that are applied. or W and Z bosons sometimes gluons
- 30. Interactions Interactions are illustratedusing Feynman diagrams. Here are two examples: Gluon exchange holds A meson interaction quarks together. (which at the quark level involves gluons) holds nucleus together
- 33. Practice : DrawFeynman diagrams to illustrate the following a) an electron absorbing a photon of energy b) a positron (anti-electron) emitting a photon of energy c) an electron-positron pair annihilation to form a photon d) Formation of an electron and positron from a photon
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- 40. Quarks (isolated quarkshave never been detected) There are six types of quarks and consequently six types of anti-quarks (with opposite charge). Generation +2/3 charge -1/3 charge 1 up (u) down (d) 2 charm (c) strange (s) 3 top (t) bottom (b) Quarks and anti-quarks combine to form hadrons. There are two classes of hadrons 3 quarks = baryon (ex. protons and neutrons) 2 quarks = meson (ex. pions)
- 41. Here are someexamples of baryons and mesons.
- 42. Baryons (three quarks) Baryonnumbers are examples of quantum numbers. Baryon numbers are +1 and -1 (anti-particles) respectively. The baryon number is conserved in any interaction. All other particles have a baryon number of zero. (only a Baryon can be +1 or -1)
- 43. Individual quarks havebaryon numbers of 1/3 (or -1/3) Protons consist of two up quarks and one down. This is written as uud and referred to as up, up, down. Note that the overall baryon number is 1/3 + 1/3 + 1/3 = 1 And the overall electrical charge would be equal to + 2/3 + 2/3 + (-1/3) = +1
- 44. Charges in quarks EZto remember Proton UUD Neutron UDD make sense?
- 45. Quarks and Spin Recall Allfermions have non-integer spin ex. electrons have spin number ½ ex. protons have spin number ½ ex. quarks have spin number ½ All bosons have integer (or zero) spin
- 46. There are twospin states referred to as UP and DOWN So spin number +½ UP spin number - ½ DOWN In a proton, the two up quarks cannot have the same spin number.
- 47. Quarks and QCD Quarksalso have different “colors”. The color force between quarks is mediated by gluons. quarks come in three colors: red, blue, green anti-quarks are : anti-red (cyan), anti-blue (yellow) and anti-green (magenta)
- 48. The “colorless” propertyof bound quarks is called confinement. Only combinations of color-neutral (add to white) quarks have been found. Baryons R + G + B = white Mesons color + anti-color = white The combination though must always be color neutral (white or colorless). This is why particles consisting of 4 quarks have never been found.
- 49. Strangeness – yetanother quantum number Depends on number of strange (-1) and anti-strange (+1) quarks in a composite particle. Only conserved in interactions involving gluons and photons. (not the WEAK force)
- 50. Interactions You do notneed to worry about the composition of baryons (other than protons and neutrons) or mesons. You should however be able to apply conservation laws to interactions. They are: Conservation of mass-energy. Conservation of baryon and lepton numbers. Conservation of electrical charge Conservation of angular momentum. Each particle has a spin number. The total spin before and after the interaction remains the same.
- 51. Practice Problem A commonprocess examined is beta decay. neutron proton + electron + anti-neutrino The anti-neutrino is required to conserve the lepton number : zero = zero + 1 – 1 uud To convert a neutron to a ? proton a down quark must change its flavor. udd
- 52. Beta decay continued: Forudd uud conversion All quarks have baryon number of 1/3 so baryon number is conserved. Charge however is not conserved. A negative charge must be removed. uud Beta decay is mediated by the weak force. The weak w- force boson w – changes the flavor of the up quark in the neutron. udd
- 53. Interactions and OtherProcesses e- uud w- Arrows pointing down in a Feynman diagram indicate anti-particles, udd NOT direction. The electron and anti-neutrino lepton numbers are + 1 and -1 so lepton number is conserved, as is electrical charge.
- 64. Elementary Particles Composite Particles Do not feel strong force Color combinations = white Lepton # = 1 Obey PEP (anti leptons = -1) Baryons Baryon # = 1 Feel strong force Baryon # = 1/3 (anti quarks = -1/3) Hadrons Gauge Bosons Mesons Obey PEP graviton & Do Not Higgs (undetected) Strong EM Weak