The Particle Zoo
This is a pedagogical tool to visualize the mass spectra of all the elementary particles and their known excitations in the Standard Model (not including the gauge bosons). The mass of the particle is represented as an energy level along the left energy axis, akin to a quantum energy level one might see for an atomic system. For visual effect, the standard names of the particles are spread out to the right at the same level as their mass. The slider bar zooms in to the low mass region and zooms out to very high mass regions (to accommodate the top quark at approximately 175 GeV/c). Baryons are in blue, mesons are in red, leptons are in purple, and quarks are in magenta. The electron, the ground state for the charged leptons, is at 0.511 MeV/c, barely above zero here on the smallest scale.
Select the particle type to generate the desired mass spectra. Zoom in or out for a better look. The data is generated using Mathematica's ParticleData functionality.
Snapshot 1: known baryon mass spectra
Snapshot 2: known meson mass spectra
Snapshot 3: low mass region highlighting the low-lying baryon, meson, lepton, and quark states
D. J. Griffiths, Introduction to Elementary Particles, 2nd ed., chapter 4, Weinheim, Germany: Wiley-VCH, 2008.