Transcript Document

How did we come to the ideas of
 quarks,
 strings?
Myron Bander
U.C. Irvine
18 May, 2003
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How do we come up with any ideas in physics?
stumble on them
Lots of data.
Arcane rules correlating the data.
More economical set of rules.
Model.
Explanation from more
fundamental principles.
Model.
Is the the model consistent,
consistent with experiment? Is it
predictive?
If yes! Theory!
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Fundamental particles.
Too many.
Introduce constituents.
Too many.
Go back two steps.
molecules to
atoms to
electron and nuclei to
proton, neutron, electron to
quarks to
?
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Particles:
charge
[symbol ]
(mass)
Spin:
Quantum Mechanics
Spin=0, 1/2, 1, 3/2, ….
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Elementary Particle Zoo circa 1960:
Spin-1/2
Spin-0
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Resonances:
Spin-1
Spin-3/2
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Symmetries:
Horizontal: Isospin back to 1930’s
Challenge: Find a
symmetry for the
whole group.
Many attempts
(1957-1961)
1961
M. Gell-Mann,
Y. Ne’eman:
(flavor) SU(3) symmetry
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SU(3) Symmetry(Cartan, ~1900):
Allowed groups: 1, 3, 6, 8, 10, . . .
o
o
o
o
o
o
Octet
o
o
o
o o
o o o
o o o o
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Decuplet
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Comparison with known (1961) particles:
OK
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Predictions:
 0 (547MeV )
 (1672MeV )
…many more borne out prediction.
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What about the 3?
d 1/ 3
u 2/ 3
spin 1/2
..can build up ALL known particles
out of these:
s 1/ 3

p  (uud )
n  (udd )
0
  (ud )   (uu , dd )   ( du )


0
……
Get a reasonable picture of many properties of
nucleons and mesons --- particle chemistry.
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Are the 3’s real?
…charge 1/3, 2/3 ?
…just mathematics, just mathematics …
real particles are in 8’s, 10’s (eight-fold-way)
1964:
maybe the 3’s are real
Gell-Mann, Zweig
quarks
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Two flies in the ointment …
Pauli Exclusion Principle
Where are the quarks?
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Where are the quarks?
Search for in:
old rocks,
sea shells,
lunar rocks,
…..
less than one part in
Try to produce
them in accelerators:
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less than one part in
1012
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Pauli Exclusion Principle:
Hydrogen
Helium
No two electrons
with the same spin
can occupy the
same orbit.
Beryllium
Lithium
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extended to quarks:
…no two identical quarks with the same spin
can be in the same orbit….
what about:
  (u 2/3 , u 2/3 , u2/3 )
  (s 1/3 , s 1/3 , s1/3 )
O.W Greenberg, Gell-Mann
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color: (+flavor)
d 1/ 3
u 2/ 3
d 1/ 3
u 2/ 3
s 1/ 3
s 1/ 3
d 1/ 3
u 2/ 3
s 1/ 3
  (s1/3 , s1/3 , s1/3 )
  (u 2/ 3 , u 2 / 3 , u 2 /3 )
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Confinement:
Forces between quarks:
no force
bungee chord
glue(on)
confined
pull too far
?
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Test in electron-positron annihilation:
hadrons
e
e


e
e
q
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e

e


e
u
q

d
u
Qq
e



d
2
R  [(2 / 3)2  (1/ 3)2  (1/ 3)2 ]
X (3?)
 (2 / 3) X (3?)
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2
1
2
3  2    3
3
3
R=3 1/3
R=2
to date: 6 quarks
c quark
threshold
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b quark
threshold
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Other tests and consequences:
 0  
Off by a factor of 3 without color.
Inelastic electron  proton scattering
Quantum Chromo Dynamics
“And since these things are so, it is necessary to think that in all
the objects that are compound there exist many things of al sorts,
and germs of all objects, having all sorts of forms and
colors and flavors”.
Anaxagoras (5th century BC)
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Strings:
• Veneziano Model
• Dual Resonance Model
• ‘bungee chords’
}
1970
elementary particles behave like
vibrating strings
(studied for a long time).
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Classical and Quantum Strings:
Strings consistent with the theory of relativity:
Nambu, Goto
OK
Strings consistent with the theory of relativity and
with quantum mechanics
..number of dimensions, unwanted particles
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Theory Of Everything:
1980: …extra dimensions, unwanted particles
may fit into a theory of gravity
TOE
….still major problems.
String theory maybe a 21st century theory,
requiring 21st century mathematics, that was
accidentally discovered in the 20th century.
Ed Witten
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