From Quarks to the Cosmos!

1
From Quarks to the Cosmos!

• Prof. Richard E. Hughes
• 3046 Physics Research Building, 614-688-5690
• Email hughes_at_mps.ohio-state.edu
• Course Web Address
• http//www.physics.ohio-state.edu/hughes/freshman
  _seminar/
• Course goals
• Particle physics and astronomy have seen
  incredible gains over the past twenty years. And
  yet, though
• particle physics concerns the very small
• astronomy concerns the extremely large,
• it is clear that these two disciplines are very
  closely related.
• This course will introduce the non-expert to
  these most exciting sciences, and describe the
  major research aims of each.
• We will focus on important questions at the
  intersection of physics and astronomy that have
  some hope of being answered over the next decade.
  

2
Course Structure

• Class meets once per week
• Each class will focus on one major research area
  in particle physics/particle astrophysics
• Many of these but not all have some participation
  by OSU physicists
• Each class will be organized like a Press
  Conference
• Except this one!
• YOU are the press
• After each class, writeup a two paragraph
  summary of the press conference
• Like you might expect to see in your local paper
• This should be easy expect it should take you
  about 30 minutes outside of class
• Prior to / after class explore topics on web
• Todays class brief introduction to particle
  physics and the important questions physicists
  are trying to answer

3
What is particle physics?

• Particle physics addresses some of the most
  fundamental questions that people have been
  pondering for centuries
• What are the building blocks of matter?
• Why are these blocks what they are? Can we
  explain their properties, such as mass?
• How do they interact?

• In a way, particle physics is complementary to
  cosmology
• cosmology studies the largest possible objects
  (such as galaxies, with hundreds of billions of
  stars!), and particle physics studies the
  smallest possible objects imaginable.

4
Building Blocks of Man
or build this!
Build this
5
Distance Scales

• Football Field 109m
• Person 1.7m
• Hand 15cm
• Mosquito 2cm
• Ant 5mm
• Human hair 100microns
• Human red blood cell, bacterium10microns
• HIV virus 100nm
• Diameter of DNA 2nm
• Width of Protein 0.5nm
• Radius of Hydrogen 25pm
• Size of the atomic nucleus 10fm
• Size of proton 1fm
• Size of quarks lt10-18m
• Planck Length 10-35m distances below this make
  no sense!

6
What is a building block?

• What is the most elementary building block of
  matter? First, we need to define elementary
• Let us define an elementary particle as something
  that
• has no discernable internal structure
• appears pointlike. (At least in current
  experiments)
• First, people thought that the atom was
  elementary

The atom, as it was envisioned around 1900
-- a ball with electrical charges inside,
bouncing around!
7
Rutherford Scattering Experiment
Rutherford Experiment
gold foil
a
Most of the atom is empty space.
Hard central core!
Like firing a cannon ball at a paper towel and
having the ball bounce back
The alpha particle is probing the structure of
the gold in the foil. This basic idea has been
repeated many times over the last hundred years
to further probe the structure of matter.
8
The atom has a rich structure!

• Eventually, it was realized that the atom is not
  elementary
• it consists of a positively charged nucleus and
  negatively charged electrons.
• The properties of outermost electrons in atoms
  give rise to chemistry and biochemistry, with all
  of its complexity!
• The electron, as far as we know, is elementary!

electron
nucleus
If the nucleus were as big as a baseball, then
the entire atom's diameter would be greater than
the length of thirty football fields!
9
Is the nucleus elementary, too?

• Unlike the electron, the nucleus is not
  structureless! It consists of protons and
  neutrons.
• But protons and neutrons are not elementary,
  either!
• They consist of quarks, which to the best of our
  knowledge are elementary.

nucleus
Experiment in 1960s
High Energy Electrons
neutron
proton
10
Break down H20
O
H
H
11
Break down Pb
12
H20 vs Pb
The sizes of the piles are different, but ratio
of u/d is not all that different and e/u ratio
is not all that different. Looking at H2O and Pb
this waythey dont look all that different.
13
The Standard Model

• The most comprehensive theory developed so far
  that explains what the matter is made out of and
  what holds it together is called the Standard
  Model.
• In the Standard Model, the elementary particles
  are
• Why do quarks and leptons come in sets (which are
  called generations)? Why are there three of
  them? We don't know.
• Note that the Standard Model is still a model
  because it's really only a theory with
  predictions that need to be tested by experiment!
• Going to very high energies the theory begins to
  breakdown. (Effective Theory)

• 6 quarks (which come in three sets)
• 6 leptons (which also come in three sets)

14
How many quarks?

• Quarks They are fundamental particlesmake up
  protons and neutronsbut other exotic forms of
  matter as well. First proposed in 1960s.

There are 6 quarks, and they come in pairs
top/truth
up
charm
1995
Where did these come from?
1974
1978
down
strange
beauty/bottom
15
What about the electron?

• We said earlier that apart from the six quarks,
  the electron was also elementary.
• It turns out that the electron is not alone --
  it belongs to a group of six particles called
  leptons! Just like quarks, leptons come in pairs

Electron neutrino
Muon neutrino
Tau neutrino
nm
nt
ne
m (mass 205 x mass of e)
t (mass 3503 x mass of e)
e
electron
muon
tau
16
What are neutrinos?

• W. Pauli postulated their existence in order to
  save the energy conservation principle in certain
  types of radioactive decays, known as
  beta-decays
• E. Fermi called them "neutrinos" -- "little
  neutrons" in Italian.
• Neutrinos hardly interact with anything at all.
  In fact, the earth receives more than 40 billion
  neutrinos per second per cm2. Most of them just
  pass through the earth, as if it's not even
  there!

neutron decays into proton plus electron plus
neutrino
17
What particles are important?
Everything you can look at contains the simple
protons neutrons, and electrons.

• So the natural expectation is that protons,
  neutrons, and electrons are the most common
  particles in the universe. But you would be very
  wrong! There are about
• 0.5 protons per cubic meter of universe
• 330 million neutrinos per cubic meter
• One billion photons per cubic meter

18
Antimatter!

• The quarks and leptons discussed so far make up
  ordinary matter.
• For every one of these there is an antimatter
  counterpart.
• Antiup quark, Antidown quark, etc.
• antielectron (positron), antielectron neutrino,
  etc.
• Antihydrogen

Explosion!
Matter
Antimatter
Never shake hands with your antiself!
An oddity as far as we can tell, all of the
luminous material we see in the universe is
MATTER not ANTI-MATTER! The predominance of
matter over antimatter in the Universe is one of
the biggest mysteries of modern high energy
physics and cosmology!
19
What holds everything together?

• Things are not falling apart because fundamental
  particles interact with each other.
• An interaction is an exchange of something.
• But what is it that particles exchange? There is
  no choice -- it has to be some other special type
  of particles! They are called force particles
  (Intermediate Vector Bosons).

A rough analogy of an interaction the two tennis
players exchange a ball
20
Four fundamental interactions

• There are four fundamental interactions between
  particles

Interaction
Mediating particle
Who feels this force
Strong
Gluon (g)
Quarks and gluons
Photon (g)
Electromagnetic
Everything electrically charged
Weak
W and Z
Quarks, leptons, photons, W, Z
Gravity
Graviton (?)
Everything!
21
The strong interaction

• The strong force holds together quarks in
  neutrons and protons.
• It's so strong, it's as if the quarks are
  super-glued to each other! So the mediating
  particles are called gluons.
• This force is unusual in that it becomes stronger
  as you try to pull quarks apart.
• Eventually, new quark pairs are produced, but no
  single quarks. That's called quark confinement.

QUARK
22
The electromagnetic interaction

• The residual electromagnetic interaction is
  what's holding atoms together in molecules.
• The mediating particle of the electromagnetic
  interaction is the photon.
• Visible light, x-rays, radio waves are all
  examples of photon fields of different energies.

opposite charges attract
23
The weak interaction

• Weak interactions are indeed weak
• Neutrinos can only interact with matter via weak
  interactions -- and so they can go through a
  light year of lead without experiencing one
  interaction!
• Weak interactions are also responsible for the
  decay of the heavier quarks and leptons.
• So the Universe appears to be made out of the
  lightest quarks (u and d), the least-massive
  charged lepton (electron), and neutrinos.

1 light year
nm
n
24
Gravity

• The Standard Model does not include gravity
  because no one knows how to do it.
• That's ok because the effects of gravity are tiny
  comparing to those from strong, electomagnetic,
  and weak interactions.
• People have speculated that the mediating
  particle of gravitational interactions is the
  graviton -- but it has not yet been observed.

25
Seething Underworld

• Lots of gluons, photons, even strange and charm
  quarks inside protons and neutrons.

26
The Big Questions

• How was matter formed at the beginning of the
  universe?
• How does it stay together?
• What are the fundamental building blocks of
  nature?
• What are the basic laws upon which the universe
  operates?
• Astrophysicists have found that less than 5
  percent of the mass of the entire universe
  consists of the kind of "luminous" matter that we
  can see. What is the dark matter that makes up
  the rest of the universe?
• Why is our universe is made of matter, while
  antimatter has all but disappeared?

27
Fermi National Accelerator Laboratory
Proton-antiproton collider Question What
are the fundamental building blocks of
nature? Only place in the world where
top quarks can be made
28
Gamma-ray Large Area Space Telescope
Gamma Ray Bursts Power at maximum up to
1,000,000,000,000,000,000 (quintillion) times the
Sun's power
Matter that radiates across the entire
electromagnetic spectrum is only 10 of the total
mass of the universe 90 of the mass of the
universe does not emit light at any wavelength.
Can detect this so-called dark matter by its
gravitational effects on luminous matter
Compton Observatory all sky gamma-ray image of
the unidentified sources (active galactic nuclei,
pulsars, supernova remnants, dense molecular
clouds, and stellar-mass black holes within our
Galaxy?)
29
ATLAS
Proton-proton collider increase energy by
factor of 7 over Fermi Tevatron! Main purpose
Search for a special particle - the Higgs
that gives all other particles MASS!
30
NUMI/MINOS
Idea make neutrinoes, shoot them underground
approximately 450 miles to Minnesota study
neutrino mass
31
Supernova / Acceleration Probe
Studying the Dark Energy of the Universe
A star's distance can be estimated from its
brightness as seen on Earth, if its total emitted
light is known the farther away it is, the
dimmer it appears. Accurate estimates of total
emitted light are possible for only a few kinds
of astronomical objects such as type Ia
supernovae most distant supernovae are dimmer
than they would be if the universe were slowing
under the influence of gravity they must be
located farther away than would be expected the
conclusion is the Universe is expanding! some
form of dark energy does indeed appear to
dominate the total mass-energy content of the
Universe, and its weird repulsive gravity is
pulling the Universe apart