What IS Matter

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What IS Matter ?

• Matter is all the stuff around you!

• Heres the picture were going to uncover(not
  all today though)

Matter
Leptons
Forces
Charged
Neutrinos
Strong
Gravity
Weak
EM
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The Quarks a Recap

• Quarks can have 3 color values red, green
  blue
• Quarks have total spin S ½ (SZ -½ or ½)
• Anti-quarks have the same mass as their quark
  does.
• Hadrons Baryons Mesons
• Baryons (antibaryons) contain 3 quarks (3
  antiquarks)
• Mesons contain a quark and an antiquark

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Why quarks?
Murray Gell-Mann 1969 Nobel Prizein Physics
Why should nature be this complicated? To
simplify the picture, and still account for this
plethora of particles which were observed,
Murray Gell-Mann proposed all these particles
were composed of just 3 smaller constituents,
called quarks.
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But even Gell-Mann doubted that they were real
An excerpt from Gell-Manns 1964 paper
A search for stable quarks of charge 1/3 or
2/3 and/or stable di-quarks of charge 2/3 or
1/3 or 4/3 at the highest energy accelerators
would help to reassure us of the non-existence
of real quarks.
In 1969, an experimentat SLAC uncovered
thefirst evidence thatprotons in fact
hadsubstructure
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If neutrons protons are not fundamental, what
about electrons?Are they made up of smaller
constituents also ?
As far as we can tell, electrons appear to be
indivisible.
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Leptons

• Electrons belong to a general class of
  particles, called Leptons
• As far as we can tell, the leptons are
  fundamental.
• Each charged lepton has an uncharged partner
  called the neutrino
• The leptons behave quite differently than the
  quarks - They dont form hadrons (no binding
  between leptons)

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Are there other types of charged leptons (like
the electron) ?

• 1932 Discovery of the positron,the
  anti-particle of the electron.
• Anti-particles really exist !!!!!
• 1937 Muons (m and m- ) discovered in cosmic
  rays.
• M(m) 200M(e)
• The muon behaves very similarly to the electron
  (i.e., itsa lepton).

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Neutrinos
1934 To account for the unseen momentum in
the reaction (decay)
n ? p e- X
X
Nobel Laureate Enrico Fermi
Fermi proposed that the unseen momentum (X) was
carried off by a particle dubbed the neutrino
(n ).
(means little neutral one)
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Discovery of the neutrino

• 1956 Existence of the neutrino confirmed at a
  nuclear reactor. (Nobel Prize)

Photon detectors
Fred Reines and Clyde Cowan, 1956
Detector H2O w/Cadmium Chloride
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How many n types are there ?
1962 An experiment at Brookhaven National Lab
showed thatthere were in fact at least 2 types
of neutrinos.
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Lepton Picture up to now
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Three happy families

• In 1975, researchers at the Stanford Linear
  Accelerator discovereda third charged lepton,
  with a mass about 3500 times that of
  theelectron. It was named the t-lepton.
• In 2000, first evidence of the ts partner, the
  tau-neutrino (nt) was announced at Fermi
  National Accelerator Lab.

3 families, just like the quarks interesting !!!
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This all looks Greek to me ?
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So heres the big picture

• Quarks and leptons are the most fundamental
  particles of nature that we know about.
• Up down quarks and electrons are the
  constituents of ordinary matter.
• The other quarks and leptons can be produced in
  cosmic ray showers or in high energy particle
  accelerators.
• Each particle has a correspondingantiparticle.

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Summarization of Matter Video Clip (5 min)
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Introduction to Forces
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The Four Fundamental Forces

• Gravity
• Weak Force
• Electromagnetic force
• Strong Force

Doesnt that looklike George W. ?
All other forces you know about can be attributed
to one of these!
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Gravity
Gravity is the weakest of the 4 forces. The
gravitational force between two objects of
masses m1 and m2, separated by a distance d
is F Gm1m2/d2 G
gravitational constant 6.7x10-11Nm2/kg2 d
distance from center-to-center The units of each
are Force Newton N mass kg
distance meters Gravity is only an
attractive force
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Electric Force The Classical Picture-
In classical physics, one charge exerts a force
on anotherby establishing a field at the
location of the other charge
The electric fieldof the charge on theright
exerts a force onthe one to the left.

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The Electric Charge and Force
The form of the electric force law between two
charges q1 and q2 separated by a separation d is
given by F kq1q2 / d2 Like the
gravitational force, F a (1/d2) k
electric constant 9x109Nm2/C2 d distance
from center-to-center Units Force
Newton N charge Coulombs C
distance meters The
electric force can be attractive or repulsive !
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Direction of Electric Forces
Opposites charges attract

-
Like charges repel


-
-
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Strong Force

• The strong force is the strongest of the known
  forces.
• It is responsible for the binding of quarks
  intobaryons and mesons. Its residual effects
  also account for the binding of protons
  neutrons in the nucleus.
• This force behaves more like a spring. That is,
  the the force actually gets stronger as quarks
  move apart!
• This in striking contrast to the EM Grav.
  Force. Their forces decreases with separation
  (recall F a 1/d2)

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Weak Force

• The weak force is the weakest of the known
  forces.
• It is responsible for neutron decay, and decays
  of heavyquarks to the lighter quarks (well see
  more of this later)
• Its interaction is very short range (as opposed
  to thelong range interactions of the EM and
  gravitational force)(well see why this is so
  later, when we talk about the weak force)

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Summary
EM
STRONG
WEAK