Transcript PHY313 - CEI544 The Mystery of Matter From Quarks to the
Peter Paul 03/03/05
PHY313 - CEI544
The Mystery of Matter From Quarks to the Cosmos
Spring 2005 Peter Paul Office Physics D-143 www.physics.sunysb.edu
PHY313 PHY313-CEI544 Spring-05 1
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 ID’s.
. 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
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.
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 2
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. • Commercial nuclear reactor use light of heavy water to moderate the neutrons, cool the fuel rods, and produce the steam that drives a turbine. • 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 • 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 and 239Plutonium as fuel. After a while the fission products from the chain reaction poison the fuel. Peter Paul 03/03/05 ITER is ready for construction and should reach ignition. PHY313-CEI544 Spring-05 3
Cosmic Timeline for the Big Bang
Quarks Peter Paul 03/03/05 deuterons proton, neutrons PHY313-CEI544 Spring-05 He nuclei( particles) 4
How are the light elements produced in stars
• Three minutes after the Big Bang the universe consisted of 75% Hydrogen, 25% 4 He less than 0.01% of D, 3 He and 7 Li.
• The sun began to burn the available H into additional 4 He, as we learned and heated itself up. • Once there was sufficient 4 He available the reaction 4 He + 4 He+ 4 He 12 C + 8 MeV became efficient. It heated the sun up still further Peter Paul 03/03/05 PHY313-CEI544 Spring-05 5
Energy from Fusion in the Sun
1
H
1
H
2
H
e
e
e
2
H
1
H
3
He
1
H
1
H
2
H
e
e
e
2
H
1
H
3
He
3
He
3
He
4
He
1
H
1
H
4 1H + 2 e 4He +2 n + 6 + 26.7 MeV energy per reaction at ~ 100 Million K temperature Peter Paul 03/03/05 PHY313-CEI544 Spring-05 6
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 4 He has accumulated to start helium burning. 4
He
4
He
8
Be
; 8
Be
4
He
12
C
• 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 Peter Paul 03/03/05 PHY313-CEI544 Spring-05 7
The CNO Cycle
• Once sufficient 12 C is available it uses H nuclei to produce all the nuclei up to 16 O in a reaction cycle.
• When sufficient 16 O is available and the star has heated up much more, the star breaks out of the CNO cycle by capture of a 4 He or a proton.
This forms all the nuclei up to 56 Fe.
• 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 Peter Paul 03/03/05 PHY313-CEI544 Spring-05 8
Relative Elemental Abundances of the Solar System
1.E+02 1.E+00 1.E-02 1.E-04 1.E-06 1.E-08 1.E-10 1.E-12 0 10 20 30 40 50 Z 60 70 80 90 100
.
At least 4 processes generate heavier elements.
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 9
Supernova explosion produces heavy elements
• When a star has burned all its light fuel, it cools and contracts under the gravitatio nal pressure. It then explodes. During the explosion huge numbers of neutrons are produced and captured rapidly by the exis ting 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.
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 10
Z Location of the r-process in the nuclear mass table
“Magic”
Chart of the
neutron
Nuclei
numbers ...+126
“Magic” proton numbers 2,8,20,28,50,82
N=Z
The r-process works its way up the mass table on the neutron rich side. There are other processes on the proton rich side Peter Paul 03/03/05
N
PHY313-CEI544 Spring-05 11
•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.
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 12
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/c 2 • 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.
• 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 Peter Paul 03/03/05 PHY313-CEI544 Spring-05 13
The production of new elementary particles
• If we bombard a target of hydrogen with an accelerated beam, of protons, a number of things can happen:
p
p
p
p p
p
p
d
p
p
x
1. Elastic scattering 2. A set of different, but known particles are produced 3. A completely unknown particle is produced • The following properties are known to be conserved: 1. Energy and momentum 2. Electric charge 3. Baryon Number number of “heavy particles Bubble chamber produces vivid pictures of the reaction Peter Paul 03/03/05 PHY313-CEI544 Spring-05 14
Bubble chamber pictures
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 15
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
m x 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 Peter Paul 03/03/05 PHY313-CEI544 Spring-05 16
“Strange” behavior of new particles
http://hyperphysics.phy astr.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 number, which he called Strangeness, must prohibit (slow down) the decay.
K
0
neutral
particle
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 17
The Particle Zoo I
• Light particles (Leptons) Species Symbol Mass electrons muons neutrinos e + , e μ + , μ 3 ’s 511 keV 105.7 MeV Very small http://hyperphysics.phy astr.gsu.edu/hbase/particles/Cronin.html
Medium heavy particles (Mesons
). All have… • Integer spin: 0,1 • Baryon number =0 Species Pions Kaons Etas Symbol + , , 0 K + , K K 0 Life time 2.6 x 10 -8 s 8.3 x 10 -17 s 1.2 x 10 -8 s 5 x 10 -8 , 10 -10 s 2.6 keV Strangeness S = 0 S = 0 S = ± 1 S = ± 1 S = 0 Mass 139.6 MeV 135 MeV 493.7 MeV 497.7 MeV 548.8 MeV Peter Paul 03/03/05 PHY313-CEI544 Spring-05 18
The Particle Zoo II
Heavy particles (Baryons): These particles all have •Half integer spin: ½; 3/2 •Baryon number B = ± 1.
Species Symbol Life time Strangeness Nucleons Hypernuclei p + n 0 0 + 0 >10 35 yrs 898 s 2.6 x 10 -10 s 0.8 x 10 -10 5.8 x 10 -20 1.5 x 10 -10 S = 0 S = 0 S = - 1 S = - 1 S = - 1 S = - 1 Mass 938.3 MeV 939.6 MeV 1116 MeV 1189 MeV 1192 MeV 1197 MeV Peter Paul 03/03/05 PHY313-CEI544 Spring-05 19
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.
• 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.
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 20
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”
u d s d u s
B = 1/3 1/3 1/3 S = 0 0 -1 Q = 2/3 -1/3 -1/3 B = -1/3 S = 0 -1/3 0 Q = -2/3 +1/3 -1/3 +1 +1/3 Peter Paul 03/03/05 PHY313-CEI544 Spring-05 21
Simple Quark configurations of hadrons
• Proton uud Q = 2/3+2/3-1/3 = +1 S = 0 B = 1 • • • • • Neutron udd Q = 2/3 -1/3 - 1/3 = 0 S = 0 B = 1 + uus Q = 2/3+2/3 -1/3 = +1 S = -1 B = 1 0 uds Q = 2/3 -1/3 – 1/3 = 0 S = -1 B = 1 0 uds Q = 2/3 - 1/3-1/3 = 0 S = -1 B = 1 dds Q = -1/3-1/3-1/3 = -1 S = -1 B = 1 Here is a problem • • • + udbar Q = =2/3 + 1/3 = 1 S=0 B = 0 0 uubar + ddbar dubar • K + usbar Q = 2/3+1/3 = 1 S = +1 B = 0 We neglected the fact that quarks with spin ½ are subject to the Pauli Principle Peter Paul 03/03/05 PHY313-CEI544 Spring-05 22
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) • The
-
(S = -3) + (S=+1) + (S=+1) and the rest then decayed into many secondary particles
.
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 23
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 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.
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 24
Deep inelastic scattering: What’s inside a nucleon?
http://hyperphysics.phy astr.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 quark antiquark pairs are constantly formed inside Peter Paul 03/03/05 PHY313-CEI544 Spring-05 quark 25
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.
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 26
Schematic description of jet event
The jet production probability can measure the strength of the strong force as a function of energy If more than 2 jets are observed they could come from Gluons Peter Paul 03/03/05 PHY313-CEI544 Spring-05 27
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.
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 28
The first events from the HERA facility at DESY proving the existence of gluons inside a proton
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 29
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 Peter Paul 03/03/05 PHY313-CEI544 Spring-05 30
Order in the (Quark) Court!
• Today we know 3 families of quarks, and 3 antiquark families.
Spin 1/2 1/2 Charge First family +3/2 -1/2 up (3 MeV) down (6 MeV) Second family Third family charm (1300 MeV) strange (100 MeV) top (175,000 MeV) bottom (4,300 MeV) http:// hyperphysics.phy-astr.gsu.edu/hbase/particles/quark.html
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 31
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 = u u d 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!
green anti-green red anti-red blue anti-blue green anti-red red anti-blue blue anti-red green anti-blue red anti-green blue anti-green Peter Paul 03/03/05 PHY313-CEI544 Spring-05 32
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
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 33
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?
Peter Paul 03/03/05 PHY313-CEI544 Spring-05 34