If the protons and neutrons in this picture were each 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.
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. Baryons are a type of hadron composed of three quarks (or three antiquarks). Mesons are a type of hadron made from a quark-antiquark pair. 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. 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. 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. 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. This chart has been made possible by the generous support of: Copyright 1988-1999 Contemporary Physics Education Project. CPEP is a non-profit organization of teachers, physicists, and educators. Send mail to: CPEP, MS 50-308, Lawrence Berkeley National Laboratory, Berkeley, CA 94720. For information on charts, text materials, hands-on classroom activites, and workshops, see http://www.cpepweb.org.
US Department of Energy
Lawrence Berkeley National Laboratory
Stanford Linear Accelerator
American Physical Society, Division of Particles and Fields
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