The Standard Model

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© 1998-2008 by Glenn Elert -- A Work in Progress
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Discussion

NEED TO FIX THIS SECTION BY INCLUDING HIGGS BOSON

introduction

The standard model is the name given in the 1970s to a theory of fundamental particles and how they interact. It incorporated all that was known about subatomic particles at the time and predicted the existence of additional particles as well.

There are sixteen named particles in the standard model, organized into the chart shown below. The last particles discovered were the W and Z bosons in 1983, the top quark in 1995, and the tauon neutrino in 2000. A seventeenth named particle, the higgs boson or higgson, has been predicted but as of 2006 it hasn't been detected.


Particles of The Standard Model [magnify]

particle families

Fundamental particles are either the building blocks of matter, called fermions, or the carriers of forces, called bosons. There are twelve fermions and four bosons in the standard model.


Fermions and Bosons [magnify]

Fermions obey a basic statistical rule described by Enrico Fermi (1901-1954) of Italy, P.A.M. Dirac (1902-1984) of England, and Wolfgang Pauli (1900-1958) of Austria called the exclusion principle. Simply stated, fermions cannot occupy the same place at the same time. (More formally, no two fermions may be described by the same quantum numbers.) Electrons and quarks are fermions, but so are things made from fermions like protons, neutrons, atoms, molecules, buildings, and people. This agrees with our macroscopic observations of matter in everyday life. People cannot walk through walls unless the wall gets out of the way.

Bosons, in contrast, have no problem coexisting in the same place at the same time. The statistical rules that bosons obey were first described by Satyendra Bose (1894-1974) of India and Albert Einstein (1879-1955) of Germany. This agrees with our macroscopic observation that light and other electromagnetic waves have no problems passing through each other. Bosons are like phantoms.

Fermions come in twelve different flavors divided into two groups of six: those which are only found in groups called quarks and those which can exist independently called leptons.


Quarks and Leptons [magnify]

The word "flavor" is used here to mean "type" and it applies only to fermions. Don't let the word mislead you. Subatomic particles are much too small to have any characteristics that could be directly observed by human senses.

As was already stated, quarks are only found in groups and never in isolation. Quarks can be grouped into triplets and doublets. The triplets are called baryons, a term derived from the Greek word βαρύς [varys] meaning "heavy". The doublets are called mesons, a term derived from the Greek word μέσος [mesos] meaning "medium". The word quark was taken from the novel Finnegan's Wake by James Joyce as spoken to the protagonist in a dream by a drunken seagull (no joke). Instead of asking for "three quarts for Mister Mark" the inebriated bird said "three quarks for Muster Mark". Since there were originally three quarks in the theory the name made some sense. Now it's just a fun word to say. Quark!

Collectively baryons (the heavy triplets), mesons (the middleweight doublets), and quarks (the fundamental particles) are known as hadrons, from the Greek word χοντρός [hadros] meaning "thick". This name alludes to the ability of the point-like quarks to bind together and form particles with size, volume, bulk, or thickness (to pick but a few synonyms).

The other fermions are called leptons, a name derived from the Greek word λεπτός [leptos] meaning "thin". As was already mentioned, these particles won't bind to each other, which keeps them "thin" in a certain sense.

The neutrinos are an important subgroup within the leptons. They come in three flavors named for their partner leptons: the electron, muon, and tauon.


The Neutrinos [magnify]

Neutrinos have very little mass (even for leptons) and interact so weakly with the rest of the particles that they are exceptionally difficult to detect. The name is a play on words. The Italian word for neutron (neutrone) sounds like the word neutral (neutro) with an augmentative suffix (-one) tacked on the end. That is, it sounds something like "big neutral" to Italian ears. Replace the augmentative suffix "-one" with the diminutive suffix "-ino" and you have a "little neutral", which is a good description of what a neutrino is -- a harmless, cute, little neutral particle. Aaaaaw.

Fermions belong to one of three known generations from ordinary (I), to exotic (II), to very exotic (III). These are not official names, but I believe they describe the differences between the generations quite well.


Fermion Generations [magnify]

Particles in group I are less massive than those in group II, which are less massive than those in group III. Within the generations, quarks are more massive than leptons and neutrinos are less massive than the other leptons.

The theme of this topic so far seems to be "names, names, names".

Particle Groups Named After Physicists
group statistics eponyms
fermions fermi - dirac Enrico Fermi
(1901 - 1954) Italy		 P.A.M. Dirac
(1902 - 1984) England
bosons bose - einstein Satyendra Bose
(1894 - 1974) India		 Albert Einstein
(1879 - 1955) Germany
classical
*particles*		 maxwell - boltzmann James Clerk Maxwell
(1831 - 1879) Scotland		 Ludwig Boltzmann
(1844 - 1906) Austria
* Classical particles (the molecules of an ideal gas, for example) are not a part of the Standard Model, but are included for comparison.
 
Particle Groups with Names of Greek Origin
group greek root meaning
hadrons χοντρός (hodros) thick
leptons λεπτός (leptos) thin
baryons βαρύς (varys) heavy
mesons μέσος (mesos) medium
hyperons υπέρ (yper) over
 
Particle Groups with Names of Latin Origin
group latin root meaning
nucleons nucleus kernel
 
Particle Groups with Names of Miscellaneous Origin
group source explanation
neutrinos Enrico Fermi
(1901-1954) Italy		 Italian diminutive form of neutron. Neutrino could be translated as "little neutral" in contrast with a neutrone, which is the "big neutral".
quarks Murray Gell-Mann
(1929-????) United States		 Synthetic, "portmanteau" word from Finnegan's Wake, a 1939 novel by the Irish modernist author James Joyce. Meant to sound like a drunken seagull ordering a quart of beer.
 

fundamental forces

introductory text


Standard Model Particle Interactions [magnify]

Particles that exist independently carry multiples of the elementary charge, while quarks carry fractional charge. Quarks always bind together in groups whose total charge is an integral multiple of the elementary charge. This is why no one has ever directly measured a fractional charge. In addition, since opposite charges attract, electrons tend to bind to protons to form atoms that are neutral overall. This is why we generally don't notice the electrical nature of matter.


Charge [magnify]

Charged particles interact by the exchange of photons -- the carrier of the electromagnetic force. The mathematical model used to describe the interaction of charged particles through the exchange of photons is known as quantum electrodynamics (QED).


The Electromagnetic Force [magnify]

Quarks and gluons also posses a characteristic known as color (or color charge). Quarks stick to other quarks because they possess color. The particles that glue them together are the appropriately named gluons. The whole phenomena is called the strong force or strong interaction since it results in forces on the small scale that overpower the electromagnetic force.


Color [magnify]

Quarks come in one of three colors: red, green, and blue. (These are just names, however. Quarks are much to small to to be visible and thus could never have a perceptual property like color.) The names were chosen because of a curious analogous relationship. The colors of quarks combine like the colors of vision. Quarks can't stand being apart from one another. They just have to join up and always seem to do so in a way that hides their overall color from the outside world. Quarks always combine in a way that makes them appear color neutral; that is, in a way that never favors one color over the other two.

Red light plus green light plus blue light appears to us humans as "colorless" white light. A baryon is a triplet of one red, one green, and one blue quark. Put them together and you get a color neutral particle. A color plus its opposite color also gives white light (red plus cyan appears white, for example). A meson is a doublet of one colored quark and one anticolored antiquark. Put them together and you also get a color neutral particle. There's something about color that makes it want to hide itself from anything bigger than a nucleus.

Gluons are also colored, but in a more complicated way than the quarks. Colored particles are bound together strongly by gluons -- the carriers of the strong force. The mathematical model used to describe the interaction of colored particles through the exchange of gluons is known as quantum chromodynamics (QCD)


The Strong Force [magnify]

There are twelve different elementary fermions. The difference between them is one of flavor.


Flavor [magnify]

Flavored particles interact weakly through the exchange of W or Z particles -- the carriers of the weak force, also known as intermediate vector bosons. The mathematical model used to describe the interaction of flavored particles through the exchange of intermediate vector bosons is known as quantum flavordynamics (QFD), but this is a term that is rarely used by practicing particle physicists. At higher energies, the weak and electromagnetic forces are indistinguishable. The mathematical model that describes both of these fundamental forces is known as electroweak theory (EWT).


The Weak Force [magnify]

All fermions are now thought to have mass. Bosons are generally massless. The exceptions to this rule are the W and Z bosons. Refinements to the standard model may eventually explain why this happens. Gluons and photons don't have rest mass (since they can never be at rest) but they do have energy, which (according to general relativity) is basically the same thing as mass.


Mass [magnify]

Gravity is the force between objects due to their mass. The mathematical model that would describe gravity on the particle level is sometimes called quantum geometrodynamics (QGD), but is more usually referred to as quantum gravitation. The standard model of particle physics does not include gravity (nor could it ever) and there currently is no quantum theory of gravitation. If there was, it would have to include a force-carying particle. The proposed name for this particle is the graviton. It is hoped that gravity will be taken care of beyond the standard model in what is often referred to as a theory of everything.

Four Fundamental Forces
aspect strong electromagnetic weak gravitation
where/when between
color charges		 between
electric charges		 during
flavor changes		 between masses
action attractive with
repulsive core		 opposites attract
likes repel		 – always attractive
strength very strong moderate moderate to weak extremely weak
range 10−15 m infinite 10−18 m infinite
particle(s) gluons photon W & Z
[& higgson?]		 [graviton?]
symbol g γ W+, W−, Z0
[H+, H−, H0]		 [????]
mass massless massless 80, 91 GeV
[>114 GeV]		 [massless]
spin 1 1 1 [0] [2]

These are some really old notes on comparative strengths of the fundamental forces. I can't remember what they mean anymore, but I can't bear to part with them.

For those who like fancy math, the standard model is described using group theory notation as …

SU(3) × SU(2) × U(1)

where the gauge group of the strong interaction is …

SU(3)

and the gauge group of the electroweak interaction is…

SU(2) × U(1)

details, details, details

stellar evolution

protostar, collapsing nebula, gravity stronger than repulsive force between atoms, gravitational attraction. Stars begin as a cloud of mostly hydrogen with about 25% helium and heavier elements in smaller quantities.

medium adult star, balance between gravity and thermal forces (essentially electromagnetic), energy comes from H-H fusion. the binding energy of a hydrogen atom is 13.6 eV while the molecular binding energy of H2 is 4.5 eV. with a surface temperature of 6000 K, the hydrogen near the surface of the sun is mostly molecular. The center of the sun is much hotter and thus the bulk of the sun is an ionized hydrogen plasma.

mature star, shift in equilibrium bloats stars like the sun, stars with masses between 0.1 and 0.5 solar masses dies, stars with a mass between 0.5 and 10 solar masses energy comes from He-He fusion to form C12 O16 Ne20 Mg24 depending on the mass of the star. (note how the numbers are all divisible by 4, the mass of helium.)

white dwarf, all atoms at zero point energy, lowest equilibrium between gravity and weak forces, mass between 0.5 and 1.4 solar masses, typical radius 5000 km (earth's radius 6400 km), density on the order of 106 g/cm3, the sun will eventually become a C12 O16 white dwarf

neutron star, pressure exceeds zero point energy, all electrons captured by protons forming neutrons, balance between strong nuclear force and gravity, mass between 1.4 and 3 solar masses, typical radius of 10 km (diameter approximately equal to the length of Manhattan), density 3 × 1014 g/cm3 comparable to that inside an atomic nucleus, from 10 to 100 solar masses fusion would eventually end with the production of Fe56 "stellar ash" although most of these stars would have ended their lives in a supernova explosion, blowing the outer layers off creating all sorts of nuclear junk while the inner layers collapsed

black hole, gravity reigns supreme, gravity is attractive and cumulative, nothing can exceed the pull of gravity, mass greater than 3 solar masses, no radius, infinite density

Summary

Problems

practice

  1. Write something.
    • Answer it.
  2. Write something.
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  3. Write something.
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  4. Write something.
    • Answer it.

numerical

  1. problems

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