How did we come to the ideas of

18 May, 2003 QuarkNet 1

How did we come to the ideas of

quarks, strings?

Myron BanderU.C. Irvine


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?


Particles:

] ( )[ charge msymb l asso

Spin:

Quantum Mechanics

Spin=0, 1/2, 1, 3/2, ….


Spin-0

Spin-1/2

Elementary Particle Zoo circa 1960:


Resonances:

Spin-1

Spin-3/2


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:


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


OK

Comparison with known (1961) particles:


Predictions:

)547(0 MeV

)1672( MeV

…many more borne out prediction.


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.


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


Two flies in the ointment …

Where are the quarks?Pauli Exclusion Principle


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


Pauli Exclusion Principle:

Hydrogen Helium

Lithium Beryllium

No two electronswith the same spin

can occupy the same orbit.


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


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


Confinement:

Forces between quarks:

bungee chordno force

confined

?

glue(on)

pull too far


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:


R=2

R=3 1/3

c quarkthreshold

b quarkthreshold

2133

3223

to date: 6 quarks


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


Strings:

• Veneziano Model• Dual Resonance Model• ‘bungee chords’ } 1970

elementary particles behave likevibrating strings

(studied for a long time).


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


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.

How did we come to the ideas of

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