Components of
the Standard Model of Fundamental Particles and Interactions

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Text on the chart:
The Standard Model
summarizes the current knowledge in Particle Physics. It is the quantum theory that includes the theory of strong interactions (quantum chromodynamics or QCD) and the unified theory of weak and electromagnetic interactions (electroweak). Gravity is included on this chart because it is one of the fundamental interactions even though not part of the "Standard Model."

Diagram of Structure within the Atom


Larger     Huge The text on the figure reads: If the protons and neutrons in this picture were 10 cm across, then the quarks and electrons would be less than 0.1 mm in size and the entire atom would be about 10 km across.

Spin is the intrinsic angular momentum of particles. Spin is given in units of h-bar, which is the quantum unit of angular momentum, where hbar = h/2pi = 6.58 x 10-25 GeV s = 1.05 x 10-34 J s.

Electric charges are given in units of the proton's charge. In SI units the electric charge of the proton is 1.60 x 10-19 coulombs.

The energy unit of particle physics is the electron volt (eV), the energy gained by one electron in crossing a potential difference of one volt. Masses are given in GeV/c2 (remember E = mc2), where 1 GeV = 109 eV = 1.60 x 10-10 joule. The mass of the proton is 0.938 GeV/c2 = 1.67 x 10-27 kg.

Chart of FERMIONS


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Chart of BOSONS


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Color Charge

Each quark carries one of the three types of "strong charge," also called "color charge." These charges have nothing to do with the colors of visible light. There are eight possible types of color charge for gluons. Just as electrically-charged particles interact by exchanging photons, in strong interactions color-charged particles interact by exchanging gluons. Leptons, photons, and W and Z bosons have no strong interaction and hence no color charge.

Quarks Confined in Mesons and Baryons

One cannot isolate quarks and gluons; they are confined in color-neutral particles called hadrons. This confinement (binding) results from multiple exchanges of gluons among the color-charged constituents. As color-charged particles (quarks and gluons) move apart, the energy in the color force between them increases. This energy eventually is converted into additional quark-antiquark pairs (see figure below). The quarks and antiquarks then combine into hadrons; these are the particles seen to emerge. Two types of hadrons have been observed in nature: mesons q qbar and baryons qqq.

Chart of Sample Fermionic Hadrons


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Chart of Sample Bosonic Hadrons


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Residual Strong Interactions

The strong binding of color-neutral protons and neutrons to form nuclei is due to residual strong interactions between their color-charged constituents. It is similar to the residual electrical interaction which binds electrically neutral atoms to form molecules. It can also be viewed as the exchange of mesons between the hadrons.


Properties of the Interactions

Chart of Properties of the Interactions

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Matter and Antimatter

For every particle type there is a corresponding antiparticle type, denoted by a bar over the particle symbol (unless + or 0 charge is shown). Particle and antiparticle have identical mass and spin but opposite charges. Some electrically neutral bosons (e.g, Z0, gamma, and eta_c = c cbar, but not K0 = dsbar) are their own antiparticles.

Figures

These diagrams are an artist's conception of physical processes. They are not exact and have no meaningful scale. Green shaded areas represent the cloud of gluons or the gluon field, and red lines the quark paths.

Neutron Decay

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The text of the figure reads: A neutron decays to a proton, an electron, and an antineutrino via a virtual (mediating) W boson. This is neutron beta decay.

eplus eminus to <i>B</i>0 <i>B</i>bar0

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The text of the figure reads: An electron and positron (antielectron) colliding at high energy can annihilate to produce B0 and Bbar0 mesons via a virtual Z boson or a virtual photon.
eta_c to piplus K0 Kminus

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The text of the figure reads: Two protons colliding at high energy can produce various hadrons plus very high mass particles such as Z bosons. Events such as this one are rare but can yield vital clues to the structure of matter.


The Particle Adventure

Visit the award-winning web feature The Particle Adventure at http://pdg.lbl.gov/cpep.html.

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