The standard model of matter
• The standard model of matter is an attempt to achieve a unified theory of matter.
• It theorises that all matter and force is composed of small elementary sub atomic particles, and is the result of all evidence we have gathered. • The subatomic particles are split into three groups as shown.

Quarks

Particle Name Symbol Electric charge
Up u $+\frac{2}{3}$
Down d $-\frac{1}{3}$
Charm c $+\frac{2}{3}$
Strange s $-\frac{1}{3}$
Top t $+\frac{2}{3}$
Bottom b $-\frac{1}{3}$
• Quarks are point-like, fundamental particles with a spin of $\frac{1}{2}$
• They also each have an anti-matter match-ups with exact opposite properties.
• For example, an anti-up quark would have a charge of $-\frac{2}/{3}$
• They are almost never by themselves, as they are affected by the strong force.
• Each quark has a spin of $\frac{1}{2}$
• This is mediated by a theory known as Quantum Chromodynamics
• Each quark has something known as a colour charge.
• There are three charges for matter: red, green and blue and three charge for antimatter: anti-red, anti-green, and anti-blue
• Quarks form products when a "white" colour charge is achieved.
• This is either a "red+green+blue" trio or a "colour+anticolour" pair.
• The products of quarks are known as Hadrons, and can be split into two major groups:
• Baryons: These are particles made of 3 quarks
• This is the "red+green+blue" combo
• Most notable ones are:
• Protons (uud)
• Neutrons (udd)
• They have half-integer spin, as they are made of 3 quarks.
• Thus they are qualified as fermions, and obey Pauli's exclusion principle
• Mesons: These are made of two quarks.
• Notable mesons are pions (anti-up+down), which mediate the strong nuclear force.
• As it is a mixture of matter and anti-matter, they decay almost instantaneously.
• They have integer or zero spin, and are treated like Bosons. Thus, they don't obey Pauli's exclusion principle.

Leptons

Particle Name Symbol Electric charge
Electron $e^{-}$ -1
Electron neutrino $v_{e}$ 0
Muon $\mu^{-}$ -1
Muon neutrino $v_{\mu}$ 0
Tau $\tau^{-}$ -1
Tau neutrino $v_{\tau}$ 0
• Leptons are fundamental particles that don't experience the strong force
• They have very little to no mass
• They are often the remnants from nuclear decay.
• Muons and Tau leptons often quickly decay into electrons with a neutrino and an antineutrino

Bosons

• Force between particles, according to the standard model, is caused by the exchange of Bosons.
• There are four basic forces: Strong, Weak, Electromagnetic and Gravity
Force Relative Strength Range (m) Force Carrier
Strong 1 $10^{-15}$ Gluons
Electromagnetic $\frac{1}{137}$ $infinite$ Photon
Weak $10^{-5}$ $10^{-17}$ W and Z Bosons
Gravity $6 \times 10^{-39}$ $infinite$ Graviton? (Yet to be discovered)
• Strong: This is the force that keeps quarks together.
• It is extremely strong, and almost always manages to prevent quarks from existing by themselves
• Its force carrier, the gluon, mediates the colour charge of quarks.
• Interestingly, the gluon itself has a colour charge.
• Electromagnetic: This is the simple electromagnetic forces on charged or magnetised objects.
• The force carrier is the photon, which we know travels at light speed.
• Quantum Electrodynamics, a subset of this study, suggests that like charges repel as they "sense" each other through exchange of photons.
• Weak: This is the force that mediates nuclear decay and other changes in colour charge
• When decay occurs, the particle decays into a W/Z boson, and immediately decays again into the proper particles
• For this reason, W/Z bosons are extremely large compared to other force carriers.
• It has been discovered that, at very very small distances ($10^{-17}m$) the electromagnetic force and the weak force have comparable strengths.
• Thus, they have concluded that the electromagnetic force and the weak force are related in a theory known as Electroweak.
• Gravity: This is the force that attracts two particles with mass together.
• Currently, it is not known whether Gravity fits with the standard model as no Graviton has ever been observed.

Pros and cons.

Pros:

• Explained the composition of subatomic particles
• Explained how forces were mediated
• Named all of the subatomic particles
• Explained interactions of subatomic particles
• Predicted existence of some particles
• Able to link several theories such as Quantum Chromodynamics, Quantum Electrodynamics and Electroweak theory.

Cons:

• Incompatible with General Relativity
• Cannot explain number of particles
• Cannot generate mechanism for the observed mass of particles (Mass of proton > Mass of its quarks)
page revision: 1, last edited: 03 Nov 2011 09:22