baudrunner's space: Rerunning the Standard Model
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Monday, August 25, 2008

Rerunning the Standard Model

The Atom

All the information contained in this article is substantiated and originates with experimental results obtained from Fermilab, Stanford, Brookhaven, CERN, et al, and is the accepted dogma of theoretical physics. This information has been lifted for the most part from an online primer of particle physics from another source and has been rewritten for the sake of brevity and for the convenience of not having to turn pages. It can be found here. Additionally, I have provided Wikipedia links for further study and clarification, but the essential purpose of this article is to comprehensibly abbreviate our compendium of knowledge of the Standard Model of the atom.

Almost all of the current evidence that we have for the existence of subatomic particles is first predicted, and then discovered. Enrico Fermi once said, “If I could remember the names of all those particles, I’d be a botanist!”

The Standard Model: 6 quarks; 6 leptons; and force carriers.

All matter is composed of leptons and quarks interacting via force carrier particles - note that gravity is not included in the Standard Model of the atom. 100's of particles are all made from the Fundamental Particles which comprise 6 quarks, 6 leptons, 6 antiquarks, 6 antileptons, and the force carriers.

Quarks make up most of the matter we see around us because the protons and neutrons are both made up of quarks. They are called: up; down; charm; strange; top; and bottom. The proton, which is charged, is made up of two up quarks and one down quark. The neutron, which is uncharged, is made up of two down quarks and one up quark.

Different quarks have different attributes. The K particle, which like the proton and neutron is also a composite particle, was the first particle found to contain the strange quark, so named because K has such a "strangely" long lifetime. The charm quark has no real charm; they just called it that and the name stuck. The bottom quark was detected at the Fermi lab in the composite particle called upsilon back in 1977, and finally the top quark was discovered in 1995 and it has the most mass of all the quarks.

We call the particles that are made up of quarks Hadrons, and they are further divided into Baryons, which are each made up of three quarks, and the very unstable Mesons, which are made up of two quarks. The two quarks that make up the Meson are a quark and an antiquark, like a pion for example, which is made up of an up quark and a down antiquark. The pion has its antiparticle, the antipion, and it is made up of a down quark and an up antiquark. Protons and neutrons are Baryons.

Photonic energy occasionally sources the creation of electron-positron pairs. The positron is the antielectron, and the two can be traced by a detector in the bubble chamber of a particle accelerator as two spiral swirls going in opposite directions from the same point of origin. "Photons" don't leave trails.

The electron is a lepton particle, as are the much more massive muon and tau, which have charges like the electron. Three types of neutrino make up the other three Leptons. Neutrinos are really hard to find because they have no charge and very little mass. All Leptons have their antimatter equivalents. Leptons appear as solitary point sources of energy with no discernible internal features. This makes them very unlike quarks, which are always seen together.

The massive Leptons do not exist around us, because when they occur, they very quickly decay into lighter leptons, like the tau particle, which decays into its corresponding neutrino, in this case a tau neutrino, and a quark and an antiquark. Electrons and neutrinos are stable and we can detect them.

A heavy Lepton can decay into another Lepton and its antineutrino. Leptons always produce their corresponding neutrinos when they decay, and observation has shown that the numbers of each Lepton remain constant, making some decay sequences impossible. In other words, electron number, muon number, and tau number and their corresponding neutrinos are always conserved when a massive lepton decays into other particles.

Neutrinos very rarely interact with other particles since they have no charge, so they can actually travel right through the Earth without touching a single other particle. They are produced in abundance during radioactive decays and their presence was inferred after physicists observed that the electron and proton produced by an at-rest decaying neutron went off into different directions, and that was odd, since they should have had their zero momentum conserved. Some other particle was providing the momentum to produce a balance and this was hypothesized to be an antineutrino. This educated guess proved right. It turns out that neutrinos are abundant.

The leptons and their corresponding neutrinos exist in three sets, as do the up and down, charm and strange, and top and bottom quarks. These are considered to be three generations of matter, organized by increasing mass. Up quarks, down quarks, and electrons make up the first generation of matter. Charm and strange quarks and muons make up the next generation, and top and bottom quarks and tau leptons the third. The unstable heavy generations do not stay around, but quickly decay into the first generation of matter. Remember that each lepton has a corresponding neutrino in its set.

Distribution of the charge types in the first generation of matter can be understood by stacking it with the electron on the bottom followed by the electron neutrino and then the down quark, and then the up quark at the top. The charge types sequence in the following order, from the top down: +2/3, -1/3, 0, 1. Neutrinos have zero charge. The charge type distributions for the muon and tau sets are the same.

There are said to be four fundamental interactions between particles - attractive and repulsive forces, decay, and annihilation. All forces are caused by one of these fundamental interactions. Force carrier particles carry these interactions and can only be absorbed or produced by a matter particle which can be affected by that particular force.

Force carrier particles allow objects like magnets to affect each other without touching. Some speculate that there might be a force carrier particle for gravity. Not me.

Photons are the electromagnetic force carriers which interact between charged particles such as electrons and protons. Neutrinos have no charge so they cannot produce or absorb photons.

Atoms usually have equal numbers of electrons and protons and their opposite charges cancel out, rendering the atom electrically neutral. Interaction occurs between atoms all the time, however, and objects stay together because the electrons of one atom are interacting with the protons of adjacent atoms, and vice versa.

The nuclei of atoms do not fly apart because the quarks that make up their Hadrons have color charge which is very strong. It is called the Strong Force and this is the force that binds quarks together to form Hadrons. The carrier particles for the quark’s color charge are called gluons. Gluons themselves have color charge but gluons are not at all like photons because photons themselves have no electromagnetic charge.

Quarks form color-balanced Hadrons, so the composite particles which they make up do not have a net color charge, and so the Strong Force only works at the very smallest of scales, where quarks interact. The force that binds quarks is strongest when they are far apart, and relaxes as the quarks come closer together.

The color charges of quarks change as gluons are exchanged with other quarks. Gluon emission and absorption always changes color. Color charges come in three types - red, green, and blue, with their antired, antigreen, and antiblue counterparts.

Mesons and Baryons are color-neutral - mesons because their quark-antiquark color charges cancel, and Baryons because the color charges of their three quarks mix to produce a neutral color charge. Gluons can be said to carry both a color and anticolor charge, since color is a conserved quantity. The color analogy satisfies the intent of physicists to describe measured observations about quarks in Hadrons.

It has been shown that there are eight different color-anticolor combinations, or eight different gluon charges, not the nine predicted by the total number of combinations of the three colors and their corresponding anticolors. The mathematics used to describe the Standard Model only accounts for eight gluon charges.

Quarks can only combine to form Baryons and Mesons, because these allow the only color combinations that confer color-neutrality on a Hadron. Particles whose quark combinations cannot permit color-neutral states are never observed. There cannot be a particle made of one up quark and one down quark, for example.

The constant exchanging of gluons between quarks makes up what physicists call a color force-field. When quarks are pulled apart their color force-fields stretch and grow stronger and at some point will even break apart to form a new quark-antiquark pair. The energy needed to create these new particles comes from the energy surplus of the color force-field of the original two quarks, which increases as it stretches. Quarks cannot exist individually.

The complexities of color conservation can be explained as follows. A red quark turns into a blue quark and emits a red/antiblue gluon. The blue color charge is cancelled by the antiblue color charge of the gluon and the red color charge of the quark is maintained. Always within a Hadron the constant gluon exchanges are made in such a way as to maintain the color-neutral state of the bound system.

The nucleus of an atom is held together by what is called the residual strong interaction between protons, which is still strong enough to overcome their electromagnetic repulsive forces.

All the stable matter in the Universe is made up of the least massive quarks (up and down) and leptons (electrons), and neutrinos, which have no mass. Weak interactions cause massive quarks and leptons to decay into lighter quarks and leptons, beyond which they can not decay.

Flavor changes are also caused by weak interactions. Flavor change refers to the decay, or transformation, of a particle into a different particle, such as a muon into an electron. The carrier particles for the weak interactions are the W+ and W- particles, which carry charge, and the neutral Z particle. These carrier particles are very massive.

Electromagnetic and weak interactions have been unified into what physicists call the electroweak theory. The strength of the weak interaction between two particles about 10^-18 meters apart is equal to that of the electromagnetic force, but becomes about 1/10,000th the strength of the electromagnetic force when the distance is increased 30 times. It becomes even smaller at normal distances for quarks in a proton or neutron, which is about 10^-15 meters.

Physicists attribute the relative strengths of the weak and electromagnetic interactions over increasing distances to the masses of the W and Z particles compared to the electromagnetic charge carriers, the photons, which have no apparent mass.

Gravity acts on all particles and objects but at the subatomic scale the effect is so small that it is not necessary to factor it into the mathematics of the Standard Model. This is convenient, because no force carrier particle for gravity has ever been observed. There is general agreement that the Standard Model needs to be extended with a new theory that will explain gravity.

Apart from their electric charge, color charge, and flavor, particles also have a property which is called spin. This does not mean that the particle is actually spinning. The term is used to describe the angular momentum and magnetic moment of the particle, properties which are demonstrated by large objects like planets and marbles.

Spin is quantized to units of 0, 1/2, 1, 3/2 (times Planck's Constant,"h") and so on. In subatomic particles such as electrons and photons, certain physical properties occur in fixed amounts Planck called “quanta”, not as a continuous range of possible values. The constant is used to calculate the values of these discrete quantities.

Another example of the nature of discrete quanta as exist in nature is that electric charges are only found as integer multiples of the electron’s charge. This is in agreement for the case of quarks, which have 1/3 and 2/3 charge but which cannot be isolated and which make up composite particles with electric charges which are integer multiples of the electron’s charge.

Particles which have odd half-integer spin (1/2, 3/2 etc.), such as quarks and leptons, and composite particles like protons and neutrons, are called fermions. These are distinguished from particles which have integer spins, such as the force carriers and the composite particles with an even number of fermions like mesons, and which are called bosons.

Bosons do not obey the Pauli Exclusion Principle, which states that no two particles in the same quantum state can occupy the same place at the same time. It was once thought that all particles obeyed this rule. Fermions obey the rule, but bosons don’t. If the nucleus of an atom contains an even number of protons and neutrons, it is a boson, otherwise it is a fermion.

Supercooled helium does not crystallize, but becomes what is called a superfluid in the condensed state. This is a strange liquid with zero viscosity and no surface tension. Only bosons can become Bose-Einstein condensates, which occur when they are cooled to within a few thousandths of a degree Kelvin above absolute zero. Their wave functions are said to overlap when they are condensed, and they exhibit the properties of a single superatom, thus violating the Pauli Exclusion Principle.

Alpha, beta, and gamma particles are the particles resulting from radioactive decay. Alpha particles are helium nuclei – two protons and two neutrons. Beta particles are electrons, and gamma radiation is a high energy photon. They can be observed when they are subjected to a magnetic field. The opposite charges of the alpha and beta particles cause them to veer in opposite directions. Gamma radiation is straight because it is unaffected by magnetism, having no charge.

Of the three forms of radiation, gamma radiation is the most penetrating, and can only be stopped by a block of lead. Beta particles can be stopped by aluminum, and alpha particles can be stopped by a sheet of paper.

A uranium 238 nucleus decays into thorium and an alpha particle. Subtracting the mass of the products from the mass of the uranium atom leaves 0.0046 amu out of the result. This loss of mass is attributable to its conversion into kinetic energy, that is, the energy of the moving particles. As Einstein said, mass is a form of energy.

Fundamental particle decay is different from radioactive decay. For one thing, fundamental particles cannot be further broken down because they have no constituents, but they can turn into other particles. A charm quark decays into a strange quark, which has less mass, and a W boson, which decays into an up quark and a down quark.

This may seem strange because the W boson’s mass is so great, but because it exists only very briefly as an intermediate particle before it decays the process does not violate the laws of conservation of energy and mass. The sum of the masses of the products plus the mass which is converted to kinetic energy equals the mass of the original pre-decay particle. Only weak interactions can change a fundamental particle into another particle.

The decay of a pi meson, or pion, through the annihilation of the quark and antiquark, produces two photons. This is an example of electromagnetic decay. Strong decay occurs when two gluons are produced through the mutual annihilation of a meson made up of a charm quark and an anticharm quark, ultimately producing hadrons.

Gluons mediate decays involving color changes. The weak force carrier particles, W+ and W-, mediate decays in which particles change flavor and electric charge.

When particles annihilate, which happens when a particle meets an antiparticle, pure energy is produced in the form of a force carrier particle which then transforms into other particles. The annihilation of an up quark and an up antiquark produces a very energetic gluon, which is transformed into a top quark and a top antiquark. The mediating particle, in this case the gluon, exists for only a billionth of a billionth of a billionth of a second, and cannot be observed.

What should be remembered is that particles are not small balls that bounce around; they have wave properties. Their exact position can never be accurately determined. They occupy a tiny localized realm wherein determining their location becomes a study in probability.

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