Fundamental Forces/Interactions

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Fundamental Forces/Interactions
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Virtual Particles, Messenger Particles, and
Vacuum Fluctuations Energy-time uncertainty
relation Assume a force has a range of
1.5 x 10-15 m. Estimate the mass of the
messenger particle for this force.
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ConcepTest 94 Compare a virtual g photon (the
messenger particle for the electromagnetic
interaction) and a virtual W particle (a
messenger for the weak nuclear interaction).
Which lives longer and which has the shorter
range? Hold up one card from each column.
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Feynman (Interaction) Diagrams, part I
Some Rules
Virtual particles begin and end on diagram
All interactions at a vertex
Each vertex only gets three lines must have at
least one incoming and at least one outgoing.

• At each vertex,
• (Electric) Charge must be conserved
• Color (Charge) must be conserved
• Baryon Number must be conserved
• Lepton Number must be conserved (by
  family)

time
Feynman Diagram Animations http//www.departments.
bucknell.edu/physics/animations/Feynman_diagrams/
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Quarks and Color and Camouflage, oh my! What is
the quark content of the D?
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ConcepTest 94 Consider the following color
combinations in various hadrons or
anti-hadrons Which color combination above
correspond to the following? Hold up as many
cards as necessary a) Meson b) Anti-Meson c)
Baryon d) Violates the colorless rule
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Consider the quark from part b). What was the
color of this second quark before it absorbed the
gluon? CAMOUFLAGE
ConcepTest 95 Consider the complete set of
colors and anti-colors a) A quark emits a
green-antired ( ) gluon. What is the color
of this quark after the gluon emission? b)
Another quark absorbs this green-antired (
) gluon. What is the color of this quark after
it absorbs this gluon?
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The Gumby Rule Consider the following
(incomplete) Feynman diagram showing a quark
changing color as it emits a gluon. Recall that
this incomplete Feynman diagram is called a
vertex. Which of the following vertices
describe allowed reactions?
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W effect on quarks In the vertex diagram shown
below, a Bd quark emits a W particle.
What particle (??) emerges after this
interaction?
W effect on leptons In the vertex diagram shown
below, an electron emits a W particle.
What particle (??) emerges after this
interaction?
Feynman Diagram Animations http//www.departments.
bucknell.edu/physics/animations/Feynman_diagrams/
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Decay Reactions and Particle Lifetimes Consider
the following four particle decays. Determine
the interaction through which each particle
decays. Then rank the particles in terms of
lifetime.