The Standard Model

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Questions and Answers

What distinguishes elementary particles from composite particles?

Composite particles do not exist in the universe.

Elementary particles have an internal structure.

Elementary particles take up space.

Composite particles can consist of two or more elementary particles. (correct)

Which of the following is NOT a fundamental fermion?

Electron

Down Quark

Photon (correct)

Up Quark

How are matter and anti-matter particles related?

They share the same charge.

They share the same mass but have opposite charges. (correct)

They are completely different particles.

They have different masses.

What is the primary function of bosons in the Standard Model?

To mediate fundamental force interactions. Signup and view all the answers

Which of the following is NOT one of the quantum numbers used to describe elementary particles?

Gravitational Charge Signup and view all the answers

What does the equation $1e = \frac{2}{3}e + \frac{2}{3}e - \frac{1}{3}e$ exemplify about particles?

The composition of a proton from quarks. Signup and view all the answers

How many flavours of quarks are present in the Standard Model?

6 Signup and view all the answers

What is the significance of the Standard Model in particle physics?

It provides a framework for understanding elementary particles and their interactions. Signup and view all the answers

What is the sum of the Baryon Numbers for a combination of three Quarks?

1 Signup and view all the answers

Which combination of particles satisfies the colour charge requirement for a Baryon?

One red, one green, one blue quark Signup and view all the answers

Which particles are examples of Leptons?

Electrons, muons, and tau particles Signup and view all the answers

What type of combination defines a Meson?

Two Quarks, one Quark and one anti-quark Signup and view all the answers

Which fundamental force is associated with the exchange of gluons?

Strong Nuclear Force Signup and view all the answers

What is required for a valid particle interaction concerning charge?

Charge must be conserved Signup and view all the answers

Which Gauge Boson is responsible for the Weak Nuclear Force?

Z and W Bosons Signup and view all the answers

Which of the following describes a Pair production phenomenon?

A photon creates an electron-positron pair Signup and view all the answers

How many types of Colour Charge are there for Quarks?

Three Signup and view all the answers

What is a characteristic of Mesons?

They are short-lived Signup and view all the answers

What does the Baryon Number conservation principle indicate?

Baryons must be equal before and after a reaction Signup and view all the answers

What is the reverse process where a photon creates matter?

Pair production Signup and view all the answers

Which of the following is an example of charge conservation during a neutron decay?

0e → 1e + −1e Signup and view all the answers

Which concept allows physicists to predict the existence of new particles?

Symmetry Signup and view all the answers

Study Notes

Elementary Particles

Elementary particles are the smallest known building blocks of the universe, with no internal structure and considered zero-dimensional points.
Types of elementary particles included are fundamental fermions (matter and antimatter) and bosons (mediators of forces).
Composite particles contain two or more elementary particles.

Matter and Antimatter

Each matter particle has a corresponding antimatter particle, denoted with a line above its symbol.
Matter and antimatter particles share the same mass but have opposite electric charges and quantum numbers.
When a matter particle collides with its antimatter counterpart, they annihilate, producing other subatomic particles.

Standard Model

The Standard Model is the mathematical framework that describes elementary particles and their interactions.
Quantum numbers guide the classification of particles, including charge, spin, baryon number, and color charge.
Example: A proton has a charge of +1e consisting of two up quarks and one down quark.

Fermions

There are 12 fermions in the Standard Model, categorized into quarks and leptons.
Six flavors of quarks: up, down, charm, strange, top, and bottom; their charges are either +2/3e or -1/3e.
Hadrons, made of quarks, are categorized as baryons (3 quarks) or mesons (2 quarks).

Color Charge

Color charge is essential for forming stable combinations of quarks, assigned as red, green, and blue (and corresponding anti-colors).
Baryons require combinations that yield a color-neutral (white) status, with protons and neutrons as common examples.
Quarks carry a baryon number of +1/3, while anti-quarks have -1/3, ensuring overall baryon number conservation.

Leptons

Unlike quarks, leptons exist independently and interact via weak nuclear force.
Common leptons include the electron, muon, and tau, each with a corresponding neutrino.
Example of interaction: Beta-minus decay involves the emission of an electron and anti-neutrino.

Fundamental Forces and Gauge Bosons

Four fundamental forces govern interactions: strong, electromagnetic, weak, and gravitational.
Gauge bosons are mediators for these forces:
- Gluon: mediates the strong nuclear force.
- Photon: carries the electromagnetic force.
- Z and W bosons: mediate weak nuclear force.
The graviton is a theoretical particle proposed for gravitational interactions.

Conservation Laws

Conservation of mass-energy and momentum is vital; annihilation produces energy based on E=mc².
Charge conservation dictates that the total charge before and after interactions must remain equal.
Baryon and lepton number conservation is essential during particle interactions to avoid discrepancies.

Neutron Decay Example

Neutron decays to a proton demonstrating conservation laws:
- Mass-energy: 939.57 → 938.27 + 0.511 + 0 + 0.779
- Charge: 0e → 1e + -1e + 0 + 0
- Baryon number: 1 → 1 + 0 + 0 + 0
- Lepton number: 0 → 0 + 1 + -1 + 0

Symmetries in Physics

Charge reversal: interactions hold when all particles are replaced with their antiparticles.
Parity symmetry: laws of physics remain unchanged if particle movements are inverted.
Time reversal: interactions can occur in reverse without violating physical laws.

CPT Symmetry

CPT (Charge, Parity, Time) symmetry implies a mirror-image universe follows the same physical laws as our own.

Supersymmetry

Supersymmetry extends the Standard Model, predicting partner particles for every Standard Model particle.
Addresses limitations in the Standard Model, particularly regarding the Higgs boson mass.