Transcript PHY313 - CEI544 The Mystery of Matter From Quarks to the

PHY313 - CEI544
The Mystery of Matter
From Quarks to the Cosmos
Spring 2005
Peter Paul
Office Physics D-143
www.physics.sunysb.edu PHY313
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Information about the Trip to BNL
• When and where: Thursday March 31, 2005 at 5:20 pm pickup by bus (free)
in the Physics Parking lot. We will drive to BNL and arrive around 6pm (20
miles). We will visit The Relativistic Heavy Ion Collider (RHIC) and its two
large experiments, Phenix and Star. Experts will be on hand to explain
research and equipment. We will return by about 7:30 pm to arrive back at
Stony Brook by 8pm.
• What are the formalities? You need to sign up either in class or to my e-mail
address [email protected]. by this Friday night. You must bring along a valid
picture ID. That’s all! The guard will go through the bus and check the picture
ID’s.
• What about private cars: You will still have to sign up and must bring a
picture ID (your drivers license) to the event. You will park your car at the lab
gate, join the bus for the tour on-site and then be driven back to your car.
• There is NO radiation hazard on site. I hope many or even most will sign up
for a unique opportunity.
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What have we learned last time
• A nuclear fission process can build up a
a chain reaction initiated by neutrons,
because each fission process produces
~3 neutrons for every one that was used.
• These neutrons need to be moderated to
low energies to be captured efficiently.
• If enough and sufficiently dense nuclear
fuel and enough low-energy neutrons
are available the reaction can be
hypercritical and take off.
• The chain reaction can be contained or
even stopped by inserting nuclei into the
fuel that have a large capability of
absorbing neutrons. Boron and
Cadmium are such nuclei.
• Fission reactors use mostly 235Uranium
and 239Plutonium as fuel. After a while
the fission products from the chain
reaction poison the fuel.
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• Commercial nuclear reactor use light of
heavy water to moderate the neutrons,
cool the fuel rods, and produce the steam
that drives a turbine.
• The fusion of deuterium and tritium
delivers huge amounts of energy/ kg of
fuel, has an infinite supply of fuel, and
produces no long-lived radioactive waste.
• However, the fusion reaction requires
~100 Million degrees temperature which
poses very difficult technical problems.
• A modern fusion reactor uses magnetic
field lines to spool the charged particles
of the plasma around in circles inside a
dough-nut shaped reactor vessel.
• The next generation Tokamac reactor
ITER is ready for construction and
should reach ignition.
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Cosmic Timeline for the Big Bang
deuterons
Quarks
proton, neutrons
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He nuclei( particles)
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How are the light elements produced in stars
• Three minutes after the Big Bang the
universe consisted of
75% Hydrogen,
25% 4He
less than 0.01% of D, 3He and 7Li.
• The sun began to burn the available H
into additional 4He, as we learned and
heated itself up.
• Once there was sufficient 4He available
the reaction
4He + 4He+ 4He  12 C + 8 MeV
became efficient. It heated the sun up
still further
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Energy from Fusion in the Sun
1
H 1H 2H  e  
e  e    
2
H  H  He  
1
3
3
1
H 1H 2H  e  
e  e    
2
H 1H 3He  
He3He4He1H 1H
4 1H + 2 e-  4He +2 n + 6  + 26.7 MeV
energy per reaction at ~ 100 Million K
temperature
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From Helium to Carbon
• When the start has used up its hydrogen, the
refraction stops and the star cools and contracts.
If the star is heavy enough the contraction will
produce enough heat near the core where the
4He has accumulated to start helium burning.
4
He 4He8Be;
8
Be 4He12C
• Because of gravity the heavier elements always
accumulate in the core of the star.
• The star now has 4 layers: at the center
accumulates the Carbon, surrounded by a He
fusion layer, surrounded by a hydrogen fusion
layer, surrounded by a dilute inert layer of
hydrogen
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The CNO Cycle
• Once sufficient 12C is available it uses H
nuclei to produce all the nuclei up to 16O
in a reaction cycle.
• When sufficient 16O is available and the
star has heated up much more, the star
breaks out of the CNO cycle by capture
of a 4He or a proton. This forms all the
nuclei up to 56Fe.
• In this process energy is produced to
heat the star further because the binding
energy/ nucleon is still increasing.
• Hans Bethe (Cornell) and Willy Fowler
(Caltech) obtained Nobel Prizes for
these discoveries
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Relative Elemental Abundances of the Solar System
1.E+02
1.E+00
% abundance
1.E-02
1.E-04
1.E-06
1.E-08
1.E-10
1.E-12
0
10
20
30
40
50
60
70
80
90
100
Z
.At least 4 processes generate heavier elements.
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Supernova explosion produces heavy elements
• When a star has burned all
its light fuel, it cools and
contracts under the gravitational pressure. It then explodes. During
the explosion huge numbers
of neutrons are produced and
captured rapidly by the existing elements (r-process).
• Beta decay changes neutrons into protons
and fills in the elements
• The new elements are blasted into space
and are collected by newly formed stars.
• Binary stars which are very hot can also
produce the heavy elements.
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“normal”
donor star
Accretion disk
Neutron star
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Location of the r-process
in
the
nuclear
mass
table
“Magic”
Chart of the
Nuclei
neutron
numbers
...+126
“Magic” proton
numbers
2,8,20,28,50,82 N=Z
Z
The r-process works its way up
the mass table on the neutronrich side. There are other
processes on the proton rich side
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N
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•Heavy elements are also created in a slow neutron capture
process, called the “s” process.
•The site for this process is in specific stage of stellar evolution,
known as the Asymptotic Giant Branch(AGB) phase.
•It occurs just before an old star expels its gaseous envelope
into the surrounding interstellar space and sometime thereafter
dies as a burnt-out, dim "white dwarf“
•They often produce beautiful nebulae like the "Dumbbell
Nebula".
•Our Sun will also end its active life this way, probably some 7
billion years from now.
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Quarks and Gluons
• After WW-II increasingly powerful
proton accelerators were able to produce
many new “elementary particles” of
increasingly heavier mass M
M = Energy of the collision/c2
• These were all strongly interacting but
some had “strange” characteristics
indicating new quantum, numbers.
• It became more and more apparent that
this many particles could not be all
fundamental and there had to be a
deeper system explaining all of this.
• In the 1970’s on purely theoretical
grounds Murray Gell-Mann introduced
a new class of sub-nucleon particles
which he called quarks.
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• The Alternating Gradient proton
Synchrotron at Brookhaven
revolutionized proton acceleration,
reaching 25 GeV in 1962
• This accelerator could produce new
particles with mass as high as 7 GeV
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The production of new elementary particles
• If we bombard a target of hydrogen • The following properties are known to
with an accelerated beam, of
be conserved:
protons, a number of things can
1. Energy and momentum
happen:
2. Electric charge
p p p p
3. Baryon Number  number of “heavy
particles
p  p  d  
p p px
1. Elastic scattering
2. A set of different, but known
particles are produced
3. A completely unknown
particle is produced
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Bubble chamber
produces vivid
pictures of the
reaction
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Bubble chamber pictures
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Energetics of elementary particle production.
• The kinetic energy of the beam and the reaction products and the energy
contained in all the masses must be conserved, i.e. must add up left and right:
for a stationary target for the three reactions above
KE ( p)  2  M P c 2  2  M p c 2  KE ( p)  KE ( p)
KE ( p)  2  M p c 2  m c 2  M d c 2  KE ( )  KE (d )
KE ( p)  2  M p c 2  M p c 2  mx c 2  KE ( x)  KE ( p)
• By knowing the masses and Kinetic Energy of the beam and target and
measuring the KE of all participants, I can determine the mass of the new
particle x
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“Strange” behavior of new particles
http://hyperphysics.phyastr.gsu.edu/hbase/particles/Cronin.html
• In the 1940’s new particles of mass ~ 500
MeV were discovered. Later confirmed at
Brookhaven
• They were first called V-particles, later
called Kaons and other particles.
• They behaved strangely:
1. They decayed into strongly interacting
particles, but with a very slow life time of
10-6 to 10-9 s.
2. They seemed to be produced in pairs:
  p K

0
3. Gell-Mann concluded that a new quantum K 0        neutral particle
number, which he called Strangeness, must
prohibit (slow down) the decay.
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The Particle Zoo I
• Light particles (Leptons)
http://hyperphysics.phyastr.gsu.edu/hbase/particles/Cronin.html
Species
Symbol
Mass
electrons
e+, e-
511 keV
Medium heavy particles (Mesons).
All have…
muons
μ+, μ-
105.7 MeV
• Integer spin: 0,1
neutrinos
3 ’s
Very small
• Baryon number =0
Species
Symbol
Pions
 + ,  -,
0
2.6 x 10-8 s
8.3 x 10-17 s
S=0
S=0
139.6 MeV
135 MeV
Kaons
K+, KK0
1.2 x 10-8s
5 x 10-8 , 10-10 s
S=±1
S=±1
493.7 MeV
497.7 MeV
Etas

2.6 keV
S=0
548.8 MeV
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Life time
Strangeness
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Mass
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The Particle Zoo II
Heavy particles (Baryons): These particles all have
•Half integer spin: ½; 3/2
•Baryon number B = ± 1.
Species
Symbol
Nucleons
p+
n0
>1035 yrs
898 s
S=0
S=0
938.3 MeV
939.6 MeV
Hypernuclei
0
+
0
-
2.6 x 10-10 s
0.8 x 10-10
5.8 x 10-20
1.5 x 10-10
S=-1
S=-1
S=-1
S=-1
1116 MeV
1189 MeV
1192 MeV
1197 MeV
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Life time
Strangeness
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Mass
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Gell-Mann and the Eight-fold Way
• In 1961 Gell-Mann and Ne‘eman
proposed a new clasification scheme to
bring simplicity into this complex zoo.
• Some observations:
1. The Mesons and Barayions interact via
the strong interaction: Hadrons
2. The mesons have between 1/3 to ½ the
mass of the Baryons. They have
interger spin (0 and 1)
3. The Baryons are the ehaviest group,
they have half-integer spin (1/2, 3/2)
4. The mesons and the Baryons seem to
be separate groups (B=0 and B=1)
5. They all have normal units of positive
and negative charges, or 0 charge.
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• These and other systematic
observations could be exxplainbed
bya mathematical classification
scheme based on the mathematical
symmetry group SU(3). It introduced
„quarks“ as a mathematical concept.
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Quarks as building blocks of Hadrons
• If Quarks are building blocks of
mesons and Baryons must have the
following properties
1. They must have spin ½: the 2 quarks
can make spin 0 or 1, 3 quarks can
make ½ and 3/2
2. They must have charges that have
1/3 or 2/3 the normal charge of an
electron!
3. There must be at least 3 different
types: “up”, “down”, and “strange”
4. We need quarks and “antiquarks”
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u
B = 1/3
S=0
Q = 2/3
d
1/3
0
-1/3
s
1/3
-1
-1/3
u
B = -1/3 S = 0 Q = -2/3
d
-1/3
0
+1/3
s
-1/3
+1
+1/3
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Simple Quark configurations of hadrons
•
•
•
•
•
•
Proton
Neutron
0
+
0
-
uud
udd
uds
uus
uds
dds
•
•
•
•
+
0
K+
udbar Q = =2/3 + 1/3 = 1
uubar + ddbar
dubar
usbar Q = 2/3+1/3 = 1
Q = 2/3+2/3-1/3 = +1 S = 0 B = 1
Q = 2/3 -1/3 - 1/3 = 0
S=0 B=1
Q = 2/3 - 1/3-1/3 = 0 S = -1 B = 1
Q = 2/3+2/3 -1/3 = +1 S = -1 B = 1
Q = 2/3 -1/3 – 1/3 = 0 S = -1 B = 1
Q = -1/3-1/3-1/3 = -1 S = -1 B = 1
S=0
Here is a
problem
B=0
S = +1 B = 0
We neglected the fact that quarks with spin ½ are subject to the Pauli Principle
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The Omega Particle
• This quark model predicts that there should be one
particle that has the simple configuration sss
• This particle has Strangeness S = -3,
Charge Q = -1
Baryon Number = -1
• When this particle was found in one bubble chamber
picture in 1964 it clinched the quark model.
• The reaction was complicated
K   p    K   K 0
(S =-1) + (S = 0)  (S = -3) + (S=+1) + (S=+1)
• The  - and the rest then decayed into many
secondary particles.
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Feynman Diagrams
http://www2.slac.stanford.edu/vvc/theory/feyn
man.html
• Richard P. Feyman invented a pictorial
way to describe the time evolution of a
reaction based on the exchange of force
particles
• In thees diagrams time is moving
forward from left to right.
• The processes here are scattering of
electrons and positrons with emission
of a photon
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Feynman was one
of the most inventive
physicists always
ready for a joke
• The process below is the annihilation
of a particle (e-) and its antiparticle
(e+) with emission of a photon. The
time axis for an antiparticle runs
backwards.
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Deep inelastic scattering: What’s inside a nucleon?
http://hyperphysics.phyastr.gsu.edu/hbase/nuclear/scatele.html
• Deep inelastic scattering of energetic
electrons is the equivalent experiment
of Rutherford's -scattering.
• Energetic electrons interact with the
charged particles (if any) inside the
proton.
• The Stanford experiment found such
particles in 1967, which were called
partons. Today we know that these are
the quarks.
• They found more than the 3 expected
partons in a proton because quarkantiquark pairs are constantly formed
inside
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quark
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Can we see quarks? Jets!
• No free quark has ever been
observed. It would have to
have 1/3 or 2/3 charge
• But quarks and antiquarks can
be seen as a shower of
secondary particles, which are
called jets. Ecah jet represent a
quark.
• We show here a spectacular
four-jet event from the CDF
detector at Fermilab.
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Schematic description of jet event
The jet production probability can measure
the strength of the strong force as a function
of energy
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If more than 2 jets are observed
they could come from Gluons
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Gluons
• Gluons are the exchange particles
between quarks.
• They are neutral particles with spin 1
• They can be seen in 3-jet events,
where a quark was struck by an
electron, and then that quark knocked
out a gluon.
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The first events from the HERA facility at DESY
proving the existence of gluons inside a proton
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The Charmed Quark
• In 1974 in a surprising result at BNL
and at SLAC a fourth quark was found.
It was named the Charmed Quark c
• It was much heavier and bound together
with an chamed antiquark into a c-cbar
state called J/. (hidden charm)
• This discovery made quarks trukly
credible. DSince then, two ehavier
quarks have been found: the b (bottom)
quark and the heaviest, the t (top) quark.
http://www.shef.ac.uk/physics/teaching/p
hy366/j-psi_files/j-psi.pdf
Sam Ting
The J/ seen as a peak at 3.1 GeV
with high-energy electron beams 
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Order in the (Quark) Court!
• Today we know 3 families of quarks, and 3 antiquark families.
Spin
Charge
First family
Second family
Third family
1/2
+3/2
up
(3 MeV)
charm
(1300 MeV)
top
(175,000 MeV)
1/2
-1/2
down
(6 MeV)
strange
(100 MeV)
bottom
(4,300 MeV)
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/quark.html
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The dynamics of quarks
• In addition to their regular quantum
numbers quarks must have other
property that differentiates them from
each other. This property is called Color.
(See e.g. the proton = uud
• There are 3 colors : Red, Green and
Blue (these are just stand-in names).
Thus the proton looks like this = uud or
any other color combination)
• The colored Quarks interact with each
other through the exchange of gluons.
These gluons exchange color between
the quarks (Color interaction).
• There are 9 color combinations but only
8 gluons. Their mass is exactly zero!
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greenanti-green
greenanti-red
greenanti-blue
redanti-red
redanti-blue
redanti-green
blueanti-blue
blueanti-red
blueanti-green
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Quark Confinement
• The color interaction between quarks
binds the quarks such that no single
quark can ever be free.
• This is different from two charged
bodies bound by the Coulomb force,
but similar to the binding of a
magnetic north-pole and a south-pole
• Thus any quark that emerges forma
proton will “dress itself with other
quarks or anti-quarks and emerge as a
jet.
• The binding force between quarks
relatively weak when they are close
together but grows stronger as they are
pulled apart.
• At close distances they can almost be
treated as free: Asymptotic freedom
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Fifth Homework Set, due March 10, 2005
1. As a star burns its hydrogen and helium fuel and later carbon oxygen,
magnesium etc, how are the ashes arranged inside the star?
2. How does a star produce the heavy elements past Fe? Describe
environment and process.
3. The observed elementary particles can be grouped by their masses in 3
groups. What are the names of these groups and what are typical masses
in each group?
4. Why are some particles called strange? Name one such strange particle.
5. Who invented quarks and where did the name come from?
6. How many quarks do we know today and what are their specific
names?
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