Standard model of fundamental particles and interactions

SMU quarknet 2008

Standard Model of Particles

What is the standard model and why do we have one?

The standard model is a theory that scientists have been looking for since people have asked ”what’s that made of?”

It consists of three simple principles1. All matter is composed of a relatively few types of

fundamental particles.2. These particles interact with each other in a few

specific ways.3. Everything that takes place in the universe results

from interactions between fundamental particles

Evolution of standard modelsAncient Greeks

•Four elementsDalton and Mendeleev

•92 elements (aye!!! Too many!!!)Thomas, Rutherford, and Chadwick

•Electron, proton, and neutron ( ah, its simple again)

The discovery of other mysterious particles ruined that idea. Then scientists had to go and predict even more particles (and find them) and the “particle zoo” was created. Not a simple system.

Some of the mysterious particles

Antimatter- just like normal matter but with an opposite charge.Muon- mysterious visitor from outer spacePion- predicted to “stick” the nucleus together.Mesons- middle sized particles (more on these later)Hyperons- particles heavier than protons and neutrons and have a “strangeness” about them.

In the late ‘60s two theories were proposed and when combined together made a model that had the few simple particles scientists wanted.

•Quantum Electrodynamics (QED)- (simplified) at high energies the electromagnetic force and the weak force are the same, the Electroweak force.

•Quantum chromodynamics (QCD)- some fundamental particles have “colors” or “colours” if your English. Its like charge but different.

Fermions- the “fundamental particles”, named after Enrico Fermi. Every thing seems to be made from a combination of these. Two types

•Leptons- small Greek coins•Quarks- almost spelled “kwork” by there discoverer? Murray Gell-Mann.

There are only four fermions “normally” in our everyday life.

•Electrons•Up quarks•Down quarks•Neutrinos

Three Generations-the more energy you put in the higher the generation. Things also get heavier

E=mc2

Non fundamental particles-made of fundamental particles Hadrons- combinations of quarks

Four Fundamental ForcesWhich is demonstrated to condense into threeWhich is theorized to condense to two Which we hope to condense into one

Gravity

Electro-magnetic

Weak

Strong

Electro-weakGrand unified theoryTheory of everything

Force carriers- forces on the quantum level are interactions between gauge bosons. A force is actually an exchange of these bosons.

Properties of the interactions- how it all fits together-

How do we know what we know?Two ways-

•Wait for things to fall apart (nuclear decay)•Smash things together and see what comes out (particle accelerators)

Problems with the Standard Model1.Higgs boson- needed to complete

the model by giving mass to particles.

2.Graviton- force carrier for gravity. Force is so weak that a particle accelerator would need to be galactic in size to achieve the energy levels needed.

3.Quantum electrodynamics and quantum chromodynamics do not play friendly with general relativity (gravity)