Download - How did we come to the ideas of
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18 May, 2003 QuarkNet 1
How did we come to the ideas of
quarks, strings?
Myron BanderU.C. Irvine
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How do we come up with any ideas in physics?
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!
Fundamental particles.Too many.Introduce constituents.Too many.Go back two steps.
stumble on them
molecules to atoms to
electron and nuclei toproton, neutron, electron to
quarks to?
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Particles:
] ( )[ charge msymb l asso
Spin:
Quantum Mechanics
Spin=0, 1/2, 1, 3/2, ….
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Spin-0
Spin-1/2
Elementary Particle Zoo circa 1960:
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Resonances:
Spin-1
Spin-3/2
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Horizontal: Isospin back to 1930’s
Challenge: Find a symmetry for the
whole group.
Many attempts(1957-1961)
1961M. Gell-Mann,Y. Ne’eman:
(flavor) SU(3) symmetry
Symmetries:
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SU(3) Symmetry(Cartan, ~1900):
Allowed groups: 1, 3, 6, 8, 10, . . .
o oo
o o o o o
oo o
o o oo o o o
Octet
Decuplet
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OK
Comparison with known (1961) particles:
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Predictions:
)547(0 MeV
)1672( MeV
…many more borne out prediction.
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What about the 3?
2/3 1/3
1/3
u d
s
spin 1/2 ..can build up ALL known particles out of these:
0
0
( ) ( )
( ) ( , ) ( )
p uud n udd
ud uu dd du
……
Get a reasonable picture of many properties of nucleons and mesons --- particle chemistry.
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Are the 3’s real?
…just mathematics, just mathematics …
…charge 1/3, 2/3 ?
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 …
Where are the quarks?Pauli Exclusion Principle
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Where are the quarks?
Search for in: old rocks, sea shells, lunar rocks, …..
Try to producethem in accelerators:
less than one part in 2210
less than one part in 1210
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Pauli Exclusion Principle:
Hydrogen Helium
Lithium Beryllium
No two electronswith the same spin
can occupy the same orbit.
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extended to quarks:
…no two identical quarks with the same spin can be in the same orbit….
what about:
O.W Greenberg, Gell-Mann
2/3 2 /3 2 /3( , , )u u u
1/3 1/3 1/3( , , )s s s
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color: (+flavor)
2/3 1/3
1/3
u d
s
2/3 1/3
1/3
u d
s
2/3 1/3
1/3
u d
s
2/ /33 2 32/( , , )u uu 1/3 1/31/3( , , )s s s
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Confinement:
Forces between quarks:
bungee chordno force
confined
?
glue(on)
pull too far
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e
e
eee
e
e
e
hadrons u
u
d
d
q
q
2qQ 2 2 2[(2 / 3) (1/ 3) (1/ 3) ]R (3?)X
(2 / 3) (3?)X
Test in electron-positron annihilation:
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R=2
R=3 1/3
c quarkthreshold
b quarkthreshold
2133
3223
to date: 6 quarks
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Other tests and consequences:
0
Inelastic electron proton scatteringQuantum Chromo Dynamics
Off by a factor of 3 without color.
“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)
Firs
t evi
d enc
e fo
r q u
ark -
like
subs
truc
t ure
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Strings:
• Veneziano Model• Dual Resonance Model• ‘bungee chords’ } 1970
elementary particles behave likevibrating 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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String theory maybe a 21st century theory, requiring 21st century mathematics, that wasaccidentally discovered in the 20th century.
Ed Witten
Theory Of Everything:
1980: …extra dimensions, unwanted particlesmay fit into a theory of gravity
TOE
….still major problems.