Standard Model of Fundamental Particles and Interactions

Standard Model of FUNDAMENTAL PARTICLES AND INTERACTIONS 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." force carriers BOSONS spin = 0, 1, 2, ... matter constituents FERMIONS spin = 1/2, 3/2, 5/2, .. Leptons spin = 1/2 Quarks spin = 1/2 Structure within Unified Electroweak spin = 1 Strong (color) spin = 1 the Atom Approx. Electric Mass Mass Electric Mass Electric Mass Electric GeV/c2 charge Name Name Flavor Flavor charge Quark GeV/c2 charge GeV/c2 charge GeV/c2 Size < 10-19 m V. electron neutrino <1x10-8 u up gluon 0.003 2/3 photon Electron Size < 10-18 m e electron0.000511 d down W- -1 0.006 -1/3 Nucleus 80.4 -1 Color Charge Each quark carries one of 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 electri- cally-charged particles interact by exchanging photons, in strong interactions color-charged par- ticles interact by exchanging gluons. Leptons, photons, and Wand Z bosons have no strong Size = 10-14 m w+ 80.4 +1 v. muon <0.0002 C charm 1.3 2/3 u neutrino z0 91.187 0.106 S strange u muon -1 0.1 -1/3 Neutron and Proton Size - 10-15 m tau <0.02 t top 175 2/3 * neutrino interactions and hence no color charge. T tau b bottom 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 ener- gy in the color-force field between them increases. This energy eventually is converted into addi- tional 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 qq and baryons qq. 1.7771 -1 4.3 -1/3 Atom Size - 10-10 m Spin is the intrinsic angular momentum of particles. Spin is given in units of h, which is the quantum unit of angular momentum, where h = h/2n = 6.58x10-25 GeV s = 1.05x10-34 J . If the then the quarks and electrons would b and neutrons in this picture were 10 cm across, s than 0.1 mm in size and the entire atom would be about 10 km across. Electric charges are given in units of the proton's charge. In SI units the electric charge of the proton is 1.60x10-19 coulombs. The energy unit of particle physics is the electronvolt (eV), the energy gained by one elec- tron in crossing a potential difference of one volt. Masses are given in GeV/c2 (remember E = mc?), where 1 GeV = 109 ev = 1.60x10-10 joule. The mass of the proton is 0.938 Geic? = 1.67x10-27 kg. Residual Strong Interaction 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 elec- trical interaction that binds electrically neutral atoms to form molecules. It can also be viewed as the exchange of mesons between the hadrons. PROPERTIES OF THE INTERACTIONS Baryons qqq and Antibaryons qqq Mesons qg Baryons are fermionic hadrons. There are about 120 types of baryons. Interaction Weak Electromagnetic Strong Mesons are bosonic hadrons. Property Gravitational There are about 140 types of mesons. (Electroweak) Fundamental Residual See Residual Strong Interaction Note Symbol Name Quark content Quark Electric charge Electric Mass charge Gev/c2 Spin Mass Acts on: Mass - Energy Flavor Electric Charge Color Charge Symbol Name content GeVic2 Spin uud Particles experiencing: All Quarks, Leptons Electrically charged Quarks, Gluons Hadrons proton 0.938 1/2 pion ud 0.140 +1 Particles mediating: Graviton (not yet observed) w+ w- z0 Gluons Mesons anti- ūūd K- sū -1 0.938 1/2 kaon -1 0.494 Strength relative to electromag 10-18 m for two u quarks at: proton 10-41 0.8 25 Not applicable to quarks p+ ud +1 0.770 neutron udd 0.940 1/2 3x10-17 m 10-41 10-4 60 Not applicable to hadrons 1 lambda uds for two protons in nucleus 10-36 10-7 во db 1.116 1/2 20 B-zero 5.279 omega -1 1.672 3/2 eta-c 2.980 n-pe- ve ete- B0 Bo pp> Z°Z0 + assorted hadrons The Particle Adventure Matter and Antimatter B0 Visit the award-winning web feature http://ParticleAdventure.org Particle Adventure at For every particle type there is a corresponding antiparticle type, denot- ed by a bar over the particle symbol (unless + or - charge is shown) Particle and antiparticle have identical mass and spin but opposite charges. Some electrically neutral bosons (e.g., 20, y, and n, = cc, but not KO = d5) are their own antiparticles. hadrons This chart has been made possible by the generous support of: d. et quarks & gluons U.S. Department of Energy hadrons gluon U.S. National Science Foundation w- Lawrence Berkeley National Laboratory Stanford Linear Accelerator Center or field hadrons 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. z0 American Physical Society, Division of Particles and Fields BURLE INDUSTRIES, INC. 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. ©2000 Contemporary Physics Education Project. CPEP is a non-profit organiza- A neutron decays to a proton, an electron, and an antineutrino via a virtual (mediating) W boson. This is neutron B decay. An electron and positron (antielectron) colliding at high energy can B annihilate to produce B° and B° mesons via a virtual Z boson or a virtual photon. tion 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 activities, and workshops, see: http://CPEPweb.org