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What’s New in Nu-clear Physics Ed V Hungerford University of Houston According to Pogo: “Nuclear Physics is not so new, and not so clear either.” 06-20,2005 UH Teacher Workshop The Answers to our questions are only as good as the questions themselves Why did the tree grow in the notch in the fence ? 06-20,2005 UH Teacher Workshop 75 years ago Nuclear Physics was New •The neutron had just been discovered •The Proton and Neutron were considered elementary particles •The nuclear force was not understood •Nuclear models were primitive and based on classical liquids Today Nuclear Physics in some sense is Mature •Nucleons are not “elementary” but are composed of other particles called quarks •The nuclear force is understood as an exchange of field quanta called gluons •The nucleus is a VERY complicated interaction of many hadrons whose interaction is described by a theory called Quantum Chromodynamics 06-20,2005 UH Teacher Workshop The Particles and Symmetries of the Standard Model 3 Families 06-20,2005 UH Teacher Workshop There are 4 known interactions in nature •One of the fundamental driving philosophies of physics is the assumption that these interactions can be “unified” •Two of these are manifestations of the same force (electroweak) •QCD is patterned after the electroweak interaction (gauge theory) •Gravity still lies outside a quantum theory •The new discovery of Dark Energy, if it is real, may imply a 5th force Field 06-20,2005 UH Teacher Workshop QCD The Interaction through Fields Particle A Particle B A Field Quanta The interaction of B with A occurs through the absorption of field quanta at B produced by A 06-20,2005 UH Teacher Workshop QCD Features • An interaction that becomes stronger the greater the distance and the lower the energy between interacting particles • A weak interaction at short distances and high energies • A permanently bound quarks and gluons • A self interaction between the field quanta (gluons) • A highly non-linear theory greatly complicating calculations and making intuitive predictions difficult • A symmetry of SU(3) expressed by 3 states of quarks and Gluons (color) 06-20,2005 UH Teacher Workshop The Quark and Gluon Constituents of the Baryon Valence Quarks Gluon Field Sea Quarks 06-20,2005 UH Teacher Workshop Quantum ChromoDynamics (QCD) is the Theory of the Strong Interaction (Nuclear Force) Quarks and Gluons 06-20,2005 Flux Tube UH Teacher Workshop Linear Potential vs distance How do we probe a Nucleon or a Nucleus To determine its Quark Content ? Incident Hadron Incident Electron 06-20,2005 UH Teacher Workshop Quark Scattering Emission of a Quark Stretches the “interaction String” When the string breaks, Quarkanti-quark pairs are produced This is called Hadronization of a Quark Jet Long Range Nuclear force Collapses to quark-antiquark Exchange (Yukawa Interaction) the “interaction String” 06-20,2005 UH Teacher Workshop Chiral Symmetry, and Mass Chiral symmetry is the fundamental symmetry of QCD Velocity Right Handed Velocity Left Handed But the particle must not have mass 06-20,2005 UH Teacher Workshop The QCD Condensate Particles acquire mass through their interaction with the vacuum, i.e. the condensate of quarks and gluons in the vacuum A nucleon in a simple visualization, is a bubble in the vacuum condensate Interaction of these quarks with the condensate at the bubble surface gives an “effective” mass to the system. Chiral Symmetry is then said to be spontaneously broken 06-20,2005 UH Teacher Workshop The Vacuum is NOT Empty This Computer simulation shows the instantaneous gluon field that might be Present in a vacuum. Red Indicates bending (winding) in the field lines perhaps a precursor to quark condensates 06-20,2005 UH Teacher Workshop Each of the 4 interactions is has its own impact on the existence of our Universe The Strong (nuclear) force is responsible for the creation and stability nuclear matter Phase Diagram of Matter We Live Here 06-20,2005 UH Teacher Workshop Studying the Vacuum and QCD Relativistic Colliding Nuclei 06-20,2005 Quark Gluon plasma UH Teacher Workshop Hadronization Connecting the very large to the very small One of the more recent advances in physics has been to connect microscopic theory to macroscopic (cosmology) For example, stellar burning and supernovae produce the nuclei of which the Universe is composed We can use this information to look back in time, as well as discuss the present features in our universe 06-20,2005 UH Teacher Workshop Mesons and baryons are composed of quarks Flavor SU(3) Symmetry Allows Placement of lowest Mesons And Baryons in Symmetry Octets 06-20,2005 UH Teacher Workshop The Nuclear Equation of State Nuclear Matter Neutron Star 06-20,2005 UH Teacher Workshop A modern cut-away view of a Neutron Star 06-20,2005 UH Teacher Workshop Measuring Matter Creation in the Galaxy 06-20,2005 UH Teacher Workshop Proton number vs Neutron Number Stability 06-20,2005 UH Teacher Workshop The Present Model of a Supernovae 06-20,2005 UH Teacher Workshop Inside a Supernova Extreme temp: photodissociates nuclei back to protons, neutrons and alphas. >8 M evolves ~107 yr 3000 km Core bounces 3x107 km Huge thermal emission of neutrinos ~5-10 seconds Neutronisation: p+e- n+ne n n n 10 km n n* n n . M n 100 km Dense core n n . M n e++e- g+g ; g+g nx + nx (all flavours equally) 06-20,2005 UH Teacher Workshop r ~ few x rnuclear Supernovae: Facts and Figures Energy release ~3x1046 J (the gravitational binding energy of the core), in about 10 seconds Equivalent to 1000 times the energy emitted by the Sun in its entire lifetime. Energy density of the core is equivalent to 1MT TNT per cubic micron. 99% of energy released is in the form of neutrinos ~1% is in the KE of the exploding matter ~0.01% is in light – and that’s enough to make it as bright as an entire galaxy. Probably site of the r-process. 06-20,2005 UH Teacher Workshop ¼ MT test (Dominic Truckee, 1962) A Computer model of a Supernovae 06-20,2005 UH Teacher Workshop A Brief Summary Nuclear Science has tremendous breadth and complexity After 75 years we have found some to the “right” questions to ask but others remain I have purposely avoided discussion of the more traditional nuclear studies There are impressive new results and insights into nuclear matter. But these require detailed exposition and are difficult to develop to grasp without some prior knowledge. As a mature, advanced science, there are significant applications in Including the fields of Medicine, Computing, Industrial Products, Energy, Finance, etc. More than 50% of the Phd graduates in Nuclear Physics are employed in industry, medicine, and national defense. 06-20,2005 UH Teacher Workshop 06-20,2005 UH Teacher Workshop