Transcript Quarks, the dreams that stuff is made of

Quarks, the dreams that stuff
is made of
Physics 100
Chapt 27
Hadron “zoo” ~1963
mesons
baryons
The elementary particle chart
revisited
1935
1963
Category
particle
symbol
Leptons
electron
e-
neutrino
n
proton
p
neutron
n
Hadrons
4 leptons: e ne; m nm
(+ 4 anti-leptons)
hundreds of hadrons
+ anti-hadrons
Economy is lost!!
1963: All hadrons known at that time
are composites of 3 types of “quarks”
and “anti-quarks” (their antiparticles)
Marray
Gell-Mann
3 quarks
“up”
George
Zweig
u+2/3
-1/3
d
“down”
(& 3 antiquarks)
u-2/3
s-1/3
“strange”
d+1/3
s+1/3
Simple Rules:
Baryons: qqq
p:
u+2/3
u+2/3
n:
L:
Mesons: q q
p+:
d-1/3
u+2/3 d-1/3
d-1/3
u+2/3 s-1/3
d-1/3
u+2/3
d+1//3
p-:
u-2/3
K 0:
s1/3
d-1/3
d-1/3
Simple Rules (cont’d):
anti-baryons: qqq
p:
u-2/3 u-2/3
d+1/3
n:
u-2/3 d1/3
d+1/3
L:
u-2/3 s1/3
d+1/3
Prediction
In the Baryon Tables at that time
there was no entry that matched
the s-1/3 s-1/3 s-1/3 combination
s-1/3 s-1/3
s-1/3
Gell-Mann called the
s-1/3 s-1/3 s-1/3 combination
the W- and predicted its
Mass & other properties
1965: the W- awas discovered at the
Brookhaven Lab in NY. It’s mass &
other properties agreed with predictions
Hadron “zoo” ~1965
mesons
baryons
!!!
Looking for sub-structure in 1905
The Rutherford
experiment
Scattering of a few a-particles
at wide angles was evidence
for the atomic nucleus
It was necessary that the
a-particles had a deBroglie
wave-length  size of nucleus
l = h/p
Looking for substructure in 1970
l = h/p
Stanford 2-mile-long accelerator
l=10-17m
World’s most
powerful micrcope
Scatter electrons from protons
q
q
Occasionally an electron
scatters at a very large angle,
Verifying expectations for quarks
q
1970 version of Rutherford’s expt
Quark theory: pros & cons
• Pros
– Explains zoo of hadrons economically
– Verified by high energy electron scattering
experiments
• Cons
– Isolated quarks have never been seen
– No explanation for qqq=baryon & qq = meson
rule
– Problems with Pauli exclusion principle
Ws-1/3 s-1/3
s-1/3
This violates my
exclusion principle
three s-quarks
in the same
quantum state
Wolfgang
Pauli
The strong interaction “charge” of
each quark comes in 3 different
varieties
O. Greenberg
Y. Nambu
Ws-1/3 s-1/3
s-1/3
the 3 s-1/3 quarks in the
W- have different charges
& thereby evade Pauli
“color” charges
Important disclaimer:
The quarks do not really have different visual colors.
It is convenient to name the different types of quark
charges after colors because of similarities in the rules
for combining them
Attractive configurations
3 primary colors
color
+ complement
same as the rules for combining colors to get white
explains the qqq=baryon & qq = meson rules
quarks: qqq  color charges
antiquarks: q q q  anticolor charges
Hence theory’s name = Quantum Chromodynamics
In QCD: force between quarks due
to exchange of “gluons”
Why are isolated quarks never
seen?
2 new mesons!!!
Pulling quarks apart is like trying to
separate the 2 ends of a rubber band.
“snapping” between quarks and
hadrons
D-
D+
1974: “charmed quark” discovered
Annihilation of
2 billion eV e- &
2 billion eV e+
e- e+  D+Dor D0D0
Particles containing a
+2/3 “charmed” quark c+2/3
Charmed quark is +2/3rds partner
of the strange quark
1975
4 quarks
(& 4 antiquarks)
+2/3
u
“up”
c+2/3“charmed”
u-2/3
c-2/3
-1/3
d
“down”
s-1/3 “strange”
d+1/3
s+1/3
Hadron “zoo” ~1975
mesons
baryons
charmed baryons
charmed mesons
Add bottom (1978) and top (1995)
This little bump
was 1st evidence
for the existence
of charge -1/3rd
“bottom” quark
The “top” quark)
(charge = +2/3rds)
was produced in very
high energy protonantiproton collisions.
UH & the top quark
Total = six quarks
Today
6 quarks
“up”
(& 6 antiquarks)
“charmed” “top”
u+2/3
c+2/3
t+2/3
u-2/3
c-2/3
t-2/3
d-1/3
s-1/3
b-1/3
d+1/3
s+1/3
b+1/3
“down” “strange” “bottom”
Six quarks more graphically
Hadron “zoo” 2005
mesons
baryons
bottom mesons
bottom baryons
The elementary particle chart
revisited
1935
Category
particle
NOW
symbol
Leptons electron
e-
neutrino
n
proton
p
neutron
n
Hadrons
Economy is maintained
(more-or-less)
Four basic forces
Name
Strong
Electromagnetic
Weak
Gravity
Propagat’d
by
gluons
photons
W & Z0
gravitons
Strongest
Weakest
Elementary Particles 2005
Gravity
Graviton Mass=0
Is that all there is?
F = G M sM p
r2
Sun
planet
v2
F = Mpa = Mp r
p = M
G M sM
p
r2
v2 = G Ms
r
V=

GMs
r
v2
r
v
Solar system rotation curve
V=

GMs
r
Milky Way Galaxy
Flat!!
Galaxies must be surrounded
by a huge amount of unseen
“dark matter”
What we see
What we don’t see
What is “dark matter”
•
No one knows
– It’s not neutrinos or unseen planets
– Maybe some as-yet undiscovered particle
•
What we do know is that there is lots of it
– Much more than ordinary matter
•
Big mystery for physicists & astronomers
– Problem for the 21st century’s Einstein
– (not me, I’m too old)
Mahalo
& good luck on the final