MOM 6

Information about MOM 6

Published on November 14, 2007

Author: Ethan

Source: authorstream.com

Content

PHY313 - CEI544 The Mystery of Matter From Quarks to the Cosmos Spring 2005:  PHY313 - CEI544 The Mystery of Matter From Quarks to the Cosmos Spring 2005 Peter Paul Office Physics D-143 www.physics.sunysb.edu PHY313 Information about the Trip to BNL:  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. What have we learned last time :  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. 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. Slide4:  Quarks Cosmic Timeline for the Big Bang proton, neutrons deuterons He nuclei( particles) How are the light elements produced in stars :  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 Energy from Fusion in the Sun:  Energy from Fusion in the Sun 4 1H + 2 e-  4He +2 n + 6  + 26.7 MeV energy per reaction at ~ 100 Million K temperature From Helium to Carbon:  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. 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 The CNO Cycle:  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 Relative Elemental Abundances of the Solar System:  Relative Elemental Abundances of the Solar System .At least 4 processes generate heavier elements. Supernova explosion produces heavy elements:  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. Location of the r-process in the nuclear mass table :  Chart of the Nuclei N Z Location of the r-process in the nuclear mass table The r-process works its way up the mass table on the neutron-rich side. There are other processes on the proton rich side Slide12:  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. Quarks and Gluons:  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. 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 The production of new elementary particles:  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: Elastic scattering A set of different, but known particles are produced A completely unknown particle is produced The following properties are known to be conserved: Energy and momentum Electric charge Baryon Number  number of “heavy particles Bubble chamber produces vivid pictures of the reaction Bubble chamber pictures:  Bubble chamber pictures Energetics of elementary particle production.:  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 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 “Strange” behavior of new particles:  “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: They decayed into strongly interacting particles, but with a very slow life time of 10-6 to 10-9 s. They seemed to be produced in pairs: Gell-Mann concluded that a new quantum number, which he called Strangeness, must prohibit (slow down) the decay. The Particle Zoo I:  The Particle Zoo I Light particles (Leptons) http://hyperphysics.phy-astr.gsu.edu/hbase/particles/Cronin.html Medium heavy particles (Mesons). All have… Integer spin: 0,1 Baryon number =0 The Particle Zoo II:  The Particle Zoo II Heavy particles (Baryons): These particles all have Half integer spin: ½; 3/2 Baryon number B = ± 1. Gell-Mann and the Eight-fold Way:  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: The Mesons and Barayions interact via the strong interaction: Hadrons The mesons have between 1/3 to ½ the mass of the Baryons. They have interger spin (0 and 1) The Baryons are the ehaviest group, they have half-integer spin (1/2, 3/2) The mesons and the Baryons seem to be separate groups (B=0 and B=1) 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. Quarks as building blocks of Hadrons :  Quarks as building blocks of Hadrons If Quarks are building blocks of mesons and Baryons must have the following properties They must have spin ½: the 2 quarks can make spin 0 or 1, 3 quarks can make ½ and 3/2 They must have charges that have 1/3 or 2/3 the normal charge of an electron! There must be at least 3 different types: “up”, “down”, and “strange” We need quarks and “antiquarks” Simple Quark configurations of hadrons:  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 0 uds Q = 2/3 - 1/3-1/3 = 0 S = -1 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 - dds Q = -1/3-1/3-1/3 = -1 S = -1 B = 1 + 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 Here is a problem We neglected the fact that quarks with spin ½ are subject to the Pauli Principle The Omega Particle :  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 (S =-1) + (S = 0)  (S = -3) + (S=+1) + (S=+1) The  - and the rest then decayed into many secondary particles. Feynman Diagrams:  Feynman Diagrams http://www2.slac.stanford.edu/vvc/theory/feynman.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. Deep inelastic scattering: What’s inside a nucleon?:  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 quark Can we see quarks? Jets!:  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. Schematic description of jet event:  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 Gluons:  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. The first events from the HERA facility at DESY proving the existence of gluons inside a proton:  The first events from the HERA facility at DESY proving the existence of gluons inside a proton The Charmed Quark:  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/phy366/j-psi_files/j-psi.pdf The J/ seen as a peak at 3.1 GeV with high-energy electron beams  Sam Ting Order in the (Quark) Court!:  Order in the (Quark) Court! http://hyperphysics.phy-astr.gsu.edu/hbase/particles/quark.html Today we know 3 families of quarks, and 3 antiquark families. The dynamics of quarks:  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! Quark Confinement :  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 Fifth Homework Set, due March 10, 2005:  Fifth Homework Set, due March 10, 2005 As a star burns its hydrogen and helium fuel and later carbon oxygen, magnesium etc, how are the ashes arranged inside the star? How does a star produce the heavy elements past Fe? Describe environment and process. 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? Why are some particles called strange? Name one such strange particle. Who invented quarks and where did the name come from? How many quarks do we know today and what are their specific names?

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