(This page still under construction)
http://en.wikipedia.org/wiki/Particle_physics
Just as atoms are known not to be the smallest particle – being made of protons, neutrons and electrons. We have to consider wether these particles are themselves fundamental or are in turn made of even smaller units. This branch of physics is called subatomic physics.
Subatomic particles: neutrons, protons, electrons, pions, neutrinos, etc…
Standard Model
http://en.wikipedia.org/wiki/Standard_Model
The current state of the classification of all elementary particles is explained by the Standard Model.
It describes the strong, weak, and electromagnetic fundamental interactions (forces), using mediating gauge bosons. The species of gauge bosons are the gluons, W−, W+ and Z bosons, and the photons.
The Standard Model also contains 24 fundamental particles, (12 particles (6 quarks and 6 leptons) and their associated anti-particles), which are the constituents of all matter.
Finally, the Standard Model also predicted the existence of a type of boson known as the Higgs boson which is responsible for the mass of particles.
Antimatter
http://en.wikipedia.org/wiki/Antimatter
Antimatter is matter composed of antiparticles. All known particles have corresponding antiparticles. Antiparticles share the same mass and spin as their matter particles but have opposite charge.
Antimatter was first proposed in 1928, by Paul Dirac. Dirac realised that his relativistic version of the Schrödinger wave equation for electrons predicted the possibility of antielectrons. These were discovered by Carl D. Anderson in 1932 and named positrons (a contraction of “positive electrons”).
Notation to represent an antiparticle is a bar on top of the symbol.
Antiparticles bind with each other to form antimatter just as ordinary particles bind to form normal matter. For example, a positron (the antiparticle of the electron) and an antiproton can form an antihydrogen atom.
Why the universe appears to be made entirely of matter is considered one of the great mysteries in Physics.
Some natural examples of antiparticles are seen in beta decay:
1. An example of electron emission (β− decay) is shown when carbon-14 decays into nitrogen-14:
14
6C → 14
7N + e− + ν
e
2. An example of positron emission (β+ decay) is shown with magnesium-23 decaying into sodium-23:
23
12Mg → 23
11Na + e+ + ν
e
Example 1 shows an antineutrino emitted and example 2 shows a positron emitted.
What Happens When Particle and Antiparticle Meet?
Encounters between particles and antiparticles lead to the annihilation of both, giving rise to high-energy photons (gamma rays), neutrinos, and lower-mass particle–antiparticle pairs.
Recall Matter and Energy are the same E=mc2.
Particle collider
Much of the understanding of particle physics comes from the deliberate annihilation of particle – antiparticle pairs. This is usually done in a particle collider the most famous of which (and largest) is the Large Hadron Collider (LHC).
LHC
http://en.wikipedia.org/wiki/Large_Hadron_Collider
http://www.wired.com/2014/03/particle-fever-lhc-clip/ – basic workings
http://www.youtube.com/user/CERNTV
www.lhc.ac.uk/
Particle colliders helped us to understand the atom that you are familiar with – protons, neutrons and electrons. But collisions with higher and higher energies allowed physicists to discover a whole new array of particles.
These seemed to fit nicely into groups or patterns in a similar way that the elements form the periodic table:
Meson Octet :
Baryon Octet:
This lead physicists to the conclusion that they weren’t seeing fundamental particles but were in fact looking at particles composed of something more fundamental.
Neutrinos
http://en.wikipedia.org/wiki/Neutrino
http://en.wikipedia.org/wiki/Neutrino_detector
The ‘missing’ momentum from many observed nuclear collisions led to the discovery of the neutrino.
The most common particle in the universe. Billions of them are streaming through your body every second.
They are light (almost massless) particles. For many years they were assumed to be massless. Now they are believed to have a very small mass (probably about one millionth the mass of an electron).
Neutrinos only interact very weakly with matter. They have no change and do not interact easily with regular matter. As such detectors must be very large in order to detect any neutrinos at all. Most detectors consist of a large tank of fluid (e.g. heavy water or chlorine) and a detector such as phototubes that watch for the Cherenkov radiation emitted when an incoming neutrino creates an electron or muon in the water.
Quarks
http://en.wikipedia.org/wiki/Quark
The fundamnetal particles that are now thought to make up the growing family of hadronic particles were named ‘quarks’. There are 6 “flavours” of quark: up, down, strange, charm, bottom, and top.
Top and Bottom are the lowest mass and most stable. The others will rapidly decay into these two.
Quarks do not exist by themselves but always exist as hadrons. A hadron is a composite particle made of quarks held together by the strong force (in a similar way as molecules are held together by the electromagnetic force).
Quarks have non-integer charges and spins.
2 types of hadrons exist:
Baryons
Baryons are made of three quarks.
The most common baryonic particles being the proton (uud) and the neutron (udd). Most of the observable matter in the universe is thus baryonic matter.
Mesons
Mesons are composed of a quark paired with an antiquark. All mesons are unstable, with the longest-lived lasting for only a fraction of a second.
Fundamental particles
Physics currently believes the following particles are ‘fundamental’ or ‘elementary’ i.e. are not made of smaller particles themselves.
http://en.wikipedia.org/wiki/Particle_physics#mediaviewer/File:Standard_Model_of_Elementary_Particles.svg
Particle Interactions (Forces)
A key part of the standard model is to understand the forces or interactions between particles.
Currently there are thought to be 4 forces in nature:
gravitational
electromagnetic
strong nuclear
weak nuclear
source: http://en.wikipedia.org/wiki/Fundamental_interaction#mediaviewer/File:Particle_overview.svg
Gravitational
As with electromagnetic this force acts over very large distances. It is by far the weakest of all of the forces.
The graviton is a hypothetical elementary particle that mediates the force of gravitation. It has not been detected and a theory to describe it is incomplete.
Electromagnetic
Electromagnetism is the force that acts between electrically charged particles. This phenomenon includes the electrostatic force acting between charged particles at rest, and the combined effect of electric and magnetic forces acting between charged particles moving relative to each other.
Electromagnetic force is transmitted through photons through Quantum Electrodynamics (QED)
Electromagnetic forces can be transmitted aver large (infinite) distances.
Strong Nuclear Force
The strong force is much stronger than electromagnetic but acts over very short distances – of the order of magnitude of the size of a nucleus. The strong force holds quarks together to form a proton and protons and neutrons together to form atomic nuclei.
The force is carried by gluons through Quantum Chromodynamics (QCD).
Weak Nuclear Force
The weak interaction is caused by the emission or absorption of W and Z bosons.
Acts over short distances.
It is responsible for quarks changing “flavour” – i.e. during beta minus decay, a down quark decays into an up quark, converting a neutron to a proton.
Feynman Diagrams
The Feynman diagram for beta-minus decay of a neutron into a proton, electron and electron anti-neutrino, via an intermediate heavy W− boson
http://en.wikipedia.org/wiki/Feynman_diagram
Higgs Boson (Higgs Particle)
The Higgs particle is an elementary particle initially theorised in 1964 and likely discovery at CERN in 2012.
It explains why some fundamental particles have mass.
https://sites.google.com/a/nygh.edu.sg/2014-s4-physics-olympiad/particle-physics