Page 29 - Topic 3

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.