Download Unit Review I – Particle Physics

Unit Review I – Particle Physics
Modern Physics
Mr. Youker |
1. Of what is a simple hydrogen atom composed and how is it held together?
A hydrogen atom is one proton as a nucleus with one electron in orbit about it.
The proton is really three colored quarks (uud) held together via the exchange of
virtual gluons. The electrically charged electron is held in orbit through the
exchange of virtual photons with the electrically charged quarks.
2. What are neutrinos and what are some of their peculiar characteristics?
Neutrinos are very light leptons. They possess some mass (maybe…) and “weak
isospin”. Therefore they interact gravitationally and via the weak force. Their
electrical and color neutrality preclude them from interacting with anything via
the two strongest forces, strong force and electro-magnetic force. Neutrino’s can
pass through lightyears of lead without interacting with anything. There are
about 100,000,000,000,000 of them passing through you each second!
3. What are ‘strange’ particles and what makes them ‘strange’?
Can you name a few?
Strange particles possess a property called ‘starngeness’. Strangeness can be
decreased incrementally though weak force interactions. This interaction takes
longer than other interactions to manifest itself… therefore the decay chain of a
strange particle takes longer than expected… its strange. An example would be…
- o + S=32
o
o
  + 2 
S = 2  1
o p+ + 
S=10
The strange baryons in the above example contain strange quarks which are
changing flavor (s  d) via the weak interaction.
4. Name the ‘flavors’ of quarks and leptons and explain what differentiates them
from one another (quarks vs leptons and flavor vs flavor).
Quarks:
Six flavors, possess color and electric charge.
up
down
 first generation “light”
strange
charm
 second generation “medium”
bottom
top
 third generation “heavy”
Leptons:
Six flavors, possess electric charge
electron
e-neutrino
 first generation “light”
muon
m-neutrino  second generation “medium”
tau
t-neutrino
 third generation “heavy”
5. What are the four fundamental forces and in what way are they modeled within
quantum field theory?
Forces are modeled through quantum fields… areas of virtual particles.
From strongest to weakest
Strong force:
mediated by gluons with limited range
Electro-magnetic force:
mediated by photons with infinite range
Weak force:
mediated by weak bosons (W and Z) with limited range
Gravitational force:
(mediated by gravitons with infinite range?)
6. What restricts the range of some bosons?
Gluons are limited in their range by their color charge.
Weak bosons are limited in their range by their mass.
7. What is meant by a “Grand Unification Theory”? How far along the path to
achieving one are scientists? What stands in their way?
A GUT is a theory that unifies the strong, EM, and weak forces together into a
single force at high temperature and energy. Scientists have achieved successful
GUT’s but are not able to incorporate gravitational force successfully to achieve
a theory of everything (TOE).
8. What is the “Eight-fold Way” and how did it allow scientists to make more
progress in their understanding of the fundamental components of the universe?
The Eight-fold Way is the conceptual foundation of Gell-Mann and Ne’eman. It is
the theory of quarks. Larger hadronic particles (protons and neutrons) can be
seen as composites of more basic particles… quarks. The population of hadrons
(baryons and mesons) had grown too large to allow these particles to act as
fundamental constituents of the universe. By introducing quarks… the number of
particles was reduced dramatically.
9. In what way have scientists been able to ‘see’ the interaction and behavior of
subatomic particles within the realm of particle physics?
Scientists can track particles as they move through space before and after their
interactions. Magnetic fields are applied to curve the paths of the particles…
positively charged particles bending one way, negative the other. The amount of
curvature also allows for measurements of energy, momentum and mass. The
laws of conservation of energy and momentum are central to analysis of particle
interactions as they cannot be violated even at that scale. Early examples of
detectors were photographic emulsions, cloud chambers, and bubble chambers.
Today’s detectors use electronic detection techniques.
10. Through what techniques were the top quark and Higg’s boson discovered?
(The two most recent - 1995 and 2012 – and significant entries into the
Standard Model)
To detect the top quark (m = 172 GeV) and Higg’s boson (m = 125 GeV) collisions
between particles with sufficiently high energies were necessary. The top quark
was “created” at Fermilab and the Higg’s boson was “created” at CERN both with
collisions between two proton beams. Their existence was inferred through their
decay into lighter mass particles.
11. What is ‘anti-matter’?
Anti-matter particles are partners to matter particles will opposite electric
charge and a few other properties. For example, there are positive antielectrons, negative anti-protons (built from anti-up quarks and anti-down
quarks). Antimatter annihilates with matter converting all mass into photons
when the two meet. The universe seems to have an extreme imbalance of
matter to antimatter (1,000,000,000 : 1) which is presently unexplained.
12. What are ‘strings’ and how could they both simplify and add complexity to our
understanding of the universe?
The various masses and properties of the particles of the Standard Model
(quarks and leptons) is unexplained by any underlying theory. In addition,
quantum field theories cannot successfully incorporate gravity into the realm of
the other forces. Quantum mechanics and general relativity remain incompatible
with one another… the one being relegated to describing the very small, the
other the very large. This all should not be. String theory is a mathematical
theory of energy, matter and interactions that attempts to successfully solve
these problems with the Standard Model. Unfortunately, the most successful
version of string theory (M-theory) describes tiny filaments of energy that
vibrate energetically at different modes across an array of eleven dimensions….
could this possibly be true?