Page 29 - Topic 3
P. 29

CONCEPT CHECK – STANDARD MODEL                           Lepton numbers can be one of three
                                                                 types:
        DO YOU KNOW?                                               − electronic lepton number,  L
                                                                                            e
         Concept                          While   Before           − muonic lepton number,  L
                                                                                         µ
                                          studying   the
                                                  test             − tauonic lepton number,  L
                                                                                          τ

         The Standard Model suggests that                        The lepton number, regardless of
         there are three fundamental types of                    type, for a lepton is 1. Antileptons
         particles: gauge bosons, leptons, and                   have a lepton number of 1. All other
         quarks.                                                 particles have a lepton number of 0.

         The Standard Model suggests that                        The baryon number of a quark is 1/3.
         there are three fundamental types of                    Baryons have a baryon number of 1.
         particles: gauge bosons, leptons, and
         quarks.                                                 Antiquarks have a baryon number of
                                                                 –1/3. Antibaryons have a baryon
         Gauge bosons are particles which                        number of –1.
         mediate the four fundamental forces.                    All other fundamental particles have
         They are often called ‘exchange                         a baryon number of 0.
         particles’.
                                                                 The laws of the conservation of
               Force       Gauge Boson                           baryon number, charge, and lepton
          Electromagnetic     photon                             number determine the types of
          Weak nuclear        W, Z                               reactions that can occur between
                                                                 particles.
          Strong nuclear      gluon
          Gravitational       graviton                           When a particle and its antiparticle
                                                                 collide, they annihilate, releasing

         The gauge boson for gravitational                       energy according to the mass–
         forces, the graviton, is still to be                    energy equivalence formula:
         discovered.                                              E =  ∆ mc 2 .

         Leptons, such as electrons, are
         particles that are not affected by the
         strong nuclear force.
                                                                CAN YOU?
         Quarks are fractionally charged
         particles that are affected by all of                   Application                     While    Before
         the fundamental forces.                                                                 Studying   the test

         Quarks combine to form composite                          •   Describe the electromagnetic,
         particles and are never directly                              weak nuclear, and strong
         observed or found in isolation.                               nuclear forces in terms of
                                                                       gauge bosons.
         There are six types of quark, with
         different properties, such as mass and                    •   Distinguish between the three
         charge. Each quark has a charge of                            types of fundamental
         either +2/3 or 1/3.                                          particles.
          Quark     Symbol    Charge (e )                          •   Describe how protons,
                                                                       neutrons, and other baryons
          Up           u         2/3                                   can be formed from different
          Down         d        1/3                                   combinations of quarks.
          Strange      s        1/3                               •   Use the conservation laws to
                                                                       determine the baryon
          Charm        c         2/3
                                                                       number, lepton number, and
          Top          t         2/3                                   charge of particles in
          Bottom       b        1/3                                   reactions.
                                                                   •   Given a reaction between
         All other composite matter particles,                         particles, demonstrate that
         such as atoms, are thought to be
         combinations of quarks and leptons.                           baryon number, lepton
                                                                       number, and charge are
         Baryons are composite particles that                          conserved.
         consist of a combination of three                         •   Solve problems using key
         quarks.
                                                                       concepts from the Standard
         Antiquarks have the opposite charge                           Model.
         to their quark equivalent. Quarks and                     •   Use the mass–energy
         antiquarks can form particles called                          equivalence relation to
         mesons.                                                       determine the energy
                                                                       released when a particle and
         Each particle is assigned a lepton
         number and a baryon number.                                   antiparticle annihilate.
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