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IB Physics SL Option D Part 2: Particle Physics

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Rodolfo Alvarado

on 27 March 2013

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Transcript of IB Physics SL Option D Part 2: Particle Physics

IB Physics SL Option D
Part 2: Particle Physics D4 Particles and Interactions D5 Quarks Description and Classification of Particles Feynman Diagrams Fundamental Interactions D4.1 State what is meant by an elementary particle. Particles are called elementary if they have no
internal structure, that is, they are not made out of
smaller constituents D4.2 Identify elementary particles. The classes of elementary particles are quarks,
leptons and exchange particles. The Higgs particle
could be elementary. D4.3 Describe particles in terms of mass and various quantum numbers. Particles (elementary as well as composite) are specified in terms of their mass and various quantum numbers. Consider electric charge, spin, strangeness, color,
lepton number and baryon number. D4.4 Classify particles according to spin. D4.5 State what is meant by an antiparticle Corresponding to most kinds of particles, there is an associated antiparticle with the same rest mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.

More examples: Up quark (+2/3) and anti-up quark (-2/3)
Neutron (0) and anti-neutron (0)
Proton (+1) and anti-proton (-1) D4.6 State the Pauli exclusion principle. The Pauli exclusion principle states that no two identical fermions (particles with half-integer spin, what is classically referred as "matter") may occupy the same quantum state simultaneously. D4.7 List the fundamental interactions. The fundamental interactions are: D4.8 Describe the fundamental interactions in terms of exchange
particles. D4.9 Discuss the uncertainty principle for time and energy in the context of particle creation. A simple discussion is needed in terms of a particle
being created with energy ΔE existing no longer
than a time Δt given by D4.10 Describe what is meant by a Feynman diagram. D4.11 Discuss how a Feynman diagram may be used to calculate probabilities for fundamental processes. Numerical values of the interaction strengths do not need to be recalled. D4.12 Describe what is meant by virtual particles. It is a particle that appears as an intermediate particle in a Feynman diagram. It is not directly observed. It temporarily violates energy/momentum
conservation. It exists for a limited time. They arise due to the time-energy uncertainty principle. D4.13 Apply the formula for the range R for interactions involving the exchange of a particle. D4.14 Describe pair annihilation and pair production through Feynman diagrams. D4.15 Predict particle processes using Feynman diagrams. By attaching known interactions in Feynman diagrams you can predict other interactions. For example, the electromagnetic interaction

leads to photon–photon scattering (that is, scattering of
light by light). The particles in the loop are electrons
or positrons: D5.1 List the six types of quark. D5.2 State the content, in terms of quarks and antiquarks, of hadrons (that is, baryons and mesons). D5.3 State the quark content of the proton and the neutron. D5.6 Explain the need for color in forming bound states of quarks. Students should realize that color is necessary
to satisfy the Pauli exclusion principle. Close fermions have very similar quantum sate, different colors allows them to be so close in state to each other.

The fact that hadrons have no color is a consequence of
confinement. Confinement is the physics phenomenon that color charged particles (such as quarks) cannot be isolated singularly, and therefore cannot be directly observed. Quarks, by default, clump together to form groups, or hadrons (mesons and baryons). D5.7 State the color of quarks and gluons. D5.8 Outline the concept of strangeness. The strangeness of a particle is a quantum number. It is defined as the number of antistrange quarks minus the number of strange quarks: D5.9 Discuss quark confinement. Students should know that isolated quarks and
gluons (that is, particles with color) cannot be

The strong (color) interaction increases
with separation. More hadrons are produced when
sufficient energy is supplied to a hadron in order to
isolate a quark. D5.10 Discuss the interaction that binds nucleons in terms of the color force between quarks. It is sufficient to know that the interaction between
nucleons is the residual interaction between the
quarks in the nucleons and that this is a short-range
interaction. D5.4 Define baryon number and apply the law of conservation of baryon number. Baryon number is the number of quarks minus the number of antiquarks, and the result is divided by 3.

A reaction is impossible if baryon number is not conserved. The same applies for charge and lepton number. For example the following interaction is impossible: D5.5 Deduce the spin structure of hadrons
(that is, baryons and mesons) Only an elementary discussion in terms of spin “up”
and spin “down” is required, these are the directions of the spin. If the particles are parallel (same spin direction) the spins add up. It the particles are antiparallel (different spin direction) the spins subtract. So for mesons (quark-antiquark pair) we can have spin -1, 0 or 1. And for hadrons (3 quarks or 3 antiquarks) we can have 3/2, 1/2, -1/2 and -3/2. Fermions: Particles with half integer spin
Examples: Quarks and leptons (electrons and neutrinos), everything classically know as matter (protons, neutrons, etc.)

Bosons: Particles with integer spin
Examples: Photon, gluon, W and Z bosons. The particles that carry a force. In such a diagram, all particles are represented by lines, with straight lines (fermions) and wavy lines/dashed lines/loops (bosons). Gluons are represented by loops. Electric charge Spin Strangeness Color Lepton number Baryon number There are two types of electric charges, called positive "+ " and negative "-". There can also be no charge "0". We can classify particles by some number representing the charge. Mass Particles can be classified according to their mass.
Generally measured in MeV c . Particles can have no mass. Particles that are not elementary are called
composite particles and they are made from
a composition of elementary particles. Examples:
Proton, charge +1
Electron, charge -1
Neutron, charge 0
Up quark, charge +2/3 Examples:
Electron: 0.51 MeV c
Proton: 938.27 MeV c
Up quark: 1.5 - 3.3 MeV c
Photon: 0 MeV c Spin is an intrinsic value carried by elementary particles. That
value is expressed differently according if the spin is parallel or anti-parallel. Examples:
Proton: Spin 1/2
Photon: Spin 1
Electron: Spin 1/2
Up quark: Spin 1/2 A number that is defined as the
number of antistrange quarks
minus the number of strange quarks: Examples:
Proton: Strangeness 0
Photon: Strangeness 0
Kaon: Strangeness 1 Color charge is a property of quarks and gluons that is related to the particles' strong interactions. Color charge is analogous with the notion of electric charge of particles. The "color" of quarks and gluons is completely unrelated to visual perception of color. The term color was chosen because the abstract property to which it refers has three kinds of values, which are analogized to the three primary colors of red, green, and blue. The analogy lies in the fact that combination of three particles with red, green and blue color charges each doesn't interact with outside color charges (it is "white"). Color charges also can be negative. For example, "anti-red" color charge is simply a negative red color charge). Examples:
Up quark with red color charge.
Up quark with blue color charge.
Gluon with antigreen color charge.
Proton has no color charge(white).
Electron has no color charge (white).
Photon has no color charge (white). In particle physics, the lepton number is the number of leptons minus the number of antileptons.

Neutron lepton number: 0
Electron lepton number: 1
Antineutrino lepton number: -1
Photon lepton number: 0 In particle physics, the baryon number is the number of quarks minus the number of antiquarks divided by 3.

Neutron baryon number: 1
Electron baryon number: 0
Neutron baryon number: 1
Photon baryon number: 0
Antineutron baryon number: -1
Up quark baryon number: 1/3 Particles are exchanged and the result is the force that we see. 0 + - We have an uncertainty in the information of a created particle in an interaction. The formula says that if you are certain on the energy you will be uncertain on the time it was created. And conversely if you are certain on the time you will be uncertain on the energy. h is plank's
constant Each point at which lines come together is called a vertex, and at each vertex one may examine the conservation laws which govern particle interactions. Each vertex must conserve charge, baryon number and lepton number. They are space-time diagrams. Regularity the time axis points upward and the space axis to the right. Other times the time is to the right and space upwards. Particles are represented by lines with arrows to denote the direction of their travel, with antiparticles having their arrows reversed. Virtual particles are represented in Feynman diagrams by wavy or broken lines and have no arrows. Classical forces — such as the electromagnetic repulsion or attraction between two charges — can be thought of as due to the exchange of many virtual photons between the charges. The Feynman diagram has an input and output and
they are useful to model the probable routes in between.
The strengths of the interactions play a role on the
path. Yukawa’s prediction of the pion. Determination of the masses of the W± , Z Where: "h" is plank's constant, "R" is the range of the interaction, "c" is the speed of light and "m" is the mass of the exchange particle. 0 To explain why the nucleons stayed together in the nucleus instead of flying away a residual
interaction resulting from the strong interaction was proposed. The exchange particle involved in this case is the composite particle ("virtual particle") named pion. From the range of the strong nuclear force (inferred from the radius of the atomic nucleus), Yukawa predicted the existence of a particle having a mass of about 100 MeV (the pion). Range of
force Photons have no mass.

As the formula says the range is infinite.

There is a relationship with the energy of the photon and the frequency of it, it is given by: The range of the weak interaction
was used to determine the mass of the W and Z bosons. These bosons are among the heavyweights of the elementary particles. The W and Z bosons are almost 100 times as massive as the proton. The masses of these bosons are significant because they act as the force carriers of a quite short-range fundamental force: their high masses thus limit the range of the weak nuclear force. In this diagram time movies forward from the bottom to the top. An arrow pointing downwards in an electron backwards in time, a "positron". When they meet they annihilate, they can also spontaneously be produced from photons. Other particle-antiparticle pairs can undergo these interactions. Up, down, charm, strange, top and bottom Mesons have a quark-antiquark pair.
Baryons can have 3 quarks or 3 antiquarks. The 3 present color charges make them "white". The colors shown here are not the only possibility.
Proton: uud
Neutron: udd Meson example
(don't memorize):
S is spin
Q is charge Quarks and gluons have color charge there are 3 charges: red, blue and green. The negative charge is anti-red (cyan), anti-blue (magenta) and anti-green (yellow). In interactions color charge is conserved.

Gluons can also carry more than one charge type. Example: red-antiblue. Strangeness is conserved during the strong and the electromagnetic interactions, but not during the weak interactions. Each particle has an antiparticle with
opposite electric charge. -2 -2 -2 -2 -2 In this section mass always refers to "rest mass".
Mass of the object when it is not moving. The previous is statement is very useful. If an interaction doesn't conserve strangeness you can infer that it is a weak interaction. Where h is the plank constant Electroweak Strong Gravitational Electromagnetic Weak Since the early 1970s the electromagnetic and weak
interactions have been shown to be two aspects of
the same interaction, the electroweak interaction. Electroweak Strong Gravitational Electromagnetic Weak The force of attraction between opposite electric charge.
The force of repulsion between opposite electric charge.
Light, magnetism and electricity. Sometimes called weak nuclear force . It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars. Weak interactions affect all known fermions. The strong interaction is observable in
two areas: on a larger scale, it is the force that binds protons and neutrons (nucleons) together to form the nucleus of an atom. On the smaller scale (the radius of a nucleon), it is the force (carried by gluons) that holds quarks together to form protons, neutrons and other hadron particles.

In the context of binding protons and neutrons together to form atoms, the strong interaction is called the nuclear force (or residual strong force). Gravitation, or gravity, is the natural phenomenon by which physical bodies appear to attract each other with a force proportional to their masses. Gluon ? It has not been observed, called "graviton" Z photon W W The exchange particle in the nuclear force (residual strong force) it's a pion (a meson).
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