Transcript Casten
Nuclear Structure – Current Directions A Thematic Overview R. F. Casten Early Universe Temperature Tc Quarks and Gluons Critical Point? Hadrons Color SuperConductor ? Nuclei Neutron stars Net Baryon Density Nucleon 100 Mean Field Models Collective models Shell Model(s) Proton Number 10 Effective Interactions Microscopic Ab Initio (GFMC...) QCD Bare Nucleon-Nucleon Interactions 1 QCD Vacuum Quark-Gluon Interactions QCD Vacuum 1 5 Neutron Number 10 50 100 The Nuclear Many-Body Problem Energy, Distance, Complexity few body heavy nuclei quarks gluons vacuum quark-gluon soup QCD nucleon QCD few body systems many body systems free NN force effective NN force The Nucleus: an integral part of nuclear science The study of nuclei is a forefront area of science that links the Standard Model, QCD phenomena, many-body systems, and the cosmos. Goal: a comprehensive description of nuclei and their reactions Nuclear structure and reactions go beyond nuclei per se: –Understanding the quantum many-body problem at variousdistance/energy scales –Testing the fundamental laws of nature –Understanding stellar evolution and the origin of the elements –Society (national security, energy, medicine…) Both theory and experiment are needed. subfemto… • How does complexity emerge from simple constituents? • How can complex systems display astonishing simplicities? nano… •Origin of NN interaction •Many-nucleon forces •Effective fields femto… Giga… Physics of Nuclei How do nuclei shape the physical universe? •In-medium interactions •Symmetry breaking •Collective dynamics •Phases and phase transitions •Chaos and order •Dynamical symmetries •Structural evolution •Origin of the elements •Energy generation in stars •Stellar evolution •Cataclysmic stellar events •Neutron-rich nucleonic matter •Electroweak processes •Nuclear matter equation of state Nuclear Structure Theory Overarching goal: To arrive at a comprehensive and unified microscopic description of all nuclei and low-energy reactions from the the basic interactions between the constituent protons and neutrons • This has been a lofty and ambitious goal in nuclear science for over fifty years • “Unified” does not mean that there is a single theoretical method that will work in all cases – Self-bound, two-component quantum many-fermion system – Complicated interaction based on QCD with at least two- and threenucleon components – We seek to describe the properties of “nuclei” ranging from the deuteron to neutron stars There is no “one size fits all” theory for nuclei, but all our theoretical approaches need to be linked by an underlying use of the constituents and the interactions between them A new era in Nuclear Structure Physics The New Frontiers of Physics with Exotic Nuclei Terra incognita — huge gene pool of nuclei Four Frontiers 1. Proton Rich Nuclei 2. Neutron Rich Nuclei 3. Heaviest Nuclei 4. Evolution of structure within these boundaries We can customize our system – fabricate “any” nucleus (designer nuclei) controlling the number of constituent protons and neutrons to isolate and amplify specific physics or interactions How does the physics of nuclei impact the physical universe? • What is the origin of elements heavier than iron? • How do stars burn and explode? • What is the nucleonic structure of neutron stars? X-ray burst 4U1728-34 331 Masses and drip lines Nuclear reaction rates Weak decay rates Electron capture rates Neutrino interactions Equation of State Fission processes 330 329 328 327 Nuclear Input (experiment and theory) 10 15 Time (s) Supernova 20 Nova neutron-Star T Pyxidis protons KS 1731-260 neutrons E0102-72.3 Themes and challenges of Modern Science •Complexity out of simplicity How the world, with all its apparent complexity and diversity can be constructed out of a few elementary building blocks and their interactions •Simplicity out of complexity How the world of complex systems can display such remarkable regularity and simplicity •Understanding the nature of the physical universe •Manipulating nature for the benefit of mankind Nuclei: Two-fluid, many-body, strongly-interacting, quantal systems provide wonderful laboratories for frontier research in all four areas Nuclear collective motion 200000 counts 150000 100000 50000 0 0 1000 energy (keV) What is the origin of ordered motion of complex nuclei? Complex systems often display astonishing simplicities. Nuclei are no exception. How is it that a heavy nucleus, with hundreds of rapidly moving nucleons, can exhibit collective motion. Two views of nuclear structure Single-particle motion Single-particle excitations with residual interactions Bulk collective motion Macroscopic shape of nuclear matter Phonons — bosons Protons, neutrons — fermions j = half-integer (orbital + intrinsic) Pauli Principle: At most 2j + 1 particles in a given orbit Microscopy, mean field, shell structure Ui Vij r = |ri - rj| = nl , E = Enl H.O. Clusters of levels shell structure r E = ħ (2n+l) E (n,l) = E (n-1, l+2) E (2s) = E (1d) Pauli Principle (≤ 2j+1 nucleons in orbit with ang. mom. j) magic numbers, inert cores, valence nucleons Many-body few-body: each body counts. Addition of 2 neutrons in a nucleus with 150 can drastically alter structure Independent Particle Motion (particles in a box) • Mottleson Importance of shell gaps, magic numbers, and shell structure is not just a matter of details but fundamental to our understanding of one of the most basic features of nuclei– independent particle motion. If we don’t understand the basic quantum levels of nucleons in the nucleus, we don’t understand nuclei. Many aspects: Changing magic numbers, intruder orbits, residual interactions, correlations, collectivity, binding (e.g., drip lines, superheavies), and regularities. Perhaps counter-intuitively, the emergence of specific forms of nuclear collectivity depends on independent particle motion (and the Pauli Principle). Pairing (in nuclei and nuclear matter) Manifestations: Energy gaps in even-even nuclei; Compression of levels in odd-A nuclei Odd-even mass differences Moments of inertia and rotational motion Quenching of Coriolis coupling Structural evolution in an Ising context; H = Hsph + HColl : Sph.-Def. Competition Structural singularities in N = Z nuclei Unique nuclear features: surface effects/finite size, kinds of Cooper pairs, Essential for existence of weakly-bound nuclei; continuum scattering Various density regimes of strength Crucial for many-body dynamics, skin modes, pair localization Connection to other fields (BECs, CSC) p-n interactions Strongest along diagonal where highest p-n overlaps occur Empirical R4/2 First direct correlation of empirical p-n interaction strengths with empirical growth rates of collectivity Approaches to nuclear structure Roadmap Ab initio Configuration interaction Density Functional Theory Collective and Algebraic Models Theoretical approaches overlap and need to be bridged Approaches to Nuclear Structure Microscopic – Approximate solutions to real nuclei • Effective Interactions • Ab initio, No core, Monte Carlo • Density Functional Theory Enormously complex, numerically intensive. However, revolutionary advances, greatly enhanced ability to predict wide variety of nuclei promise of a comprehensive theory Macroscopic – Exact solutions to ideal nuclei Geometric symmetries. Simple patterns, quantum nos., Selection rules • • Analytic, Intuitive understanding -- WHAT symmetries? Challenge to microscopy – Why THESE symmetries, which nuclei, why in THESE nuclei? Ab initio: GFMC, NCSM, CCM (nuclei, neutron droplets, nuclear matter) NN NNN 1-2% calculations of A = 6 – 12 nuclear energies are possible excited states with the same quantum numbers computed S. Pieper, ANL Asymptotic Freedom (for theorists) Density Functional Theory New Features in Weakly Bound Nuclei Spatially extended wave functions V (r) Halo Nuclei Normal nuclear density 11Li p-n core Density (log) r n-skin 0 r 10 20 Radius (fm) Diffuse V (r) Normal potential Altered shell structure New form of matter – low density, diffuse, spatially extended, nearly pure neutron matter Possible Changes in Structure for Skin Nuclei J. Dobaczewski and W. Nazarewicz h9/2 f5/2 p1/2 p3/2 f7/2 h11/2 g7/2 d3/2 s1/2 d5/2 g9/2 N=5 126 3p 2f 1h N=4 82 3s 2d 1g p1/2 f5/2 i13/ p23/2 h9/2 f7/2 d3/2 h11/2 s1/2 g7/2 d5/2 50 g9/2 very diffuse surface neutron drip line harmonic oscillator no spin orbit exotic nuclei/ hypernuclei around the valley of b-stability SUPERHEAVIES Classifying Structure -- The Symmetry Triangle of Collective Behavior Dynamical Symmetries, Phase Transitions, Critical Point Symmetries, Order and Chaos E(5) Deformed Sph. X(5) Landau Theory Complementarity of macroscopic and microscopic approaches. Why do certain nuclei exhibit specific symmetries and not others? Why these specific evolutionary trajectories? What unknown regularities appear along the Arc? What will happen far from stability? Neutron “skins” near the neutron drip line Outer regions of low density nearly pure neutron matter Skins and Skin Modes n p Production and use of Exotic Isotopes High Energy Heavy Ion Driver Intense Stable Ion Beam Fragmentation Target and Ion Separator Exotic Ion Beam Gas Stopping High Energy Proton Driver Intense Proton Beam ISOL Target/Ion Extraction Exotic Ions Fast Beam Experiments Stopped Beam Experiments (Traps) Second Accelerator Exotic Ion Beam Reaccelerated Beam Experiments Radioactive Ion Beam Facilities Timeline ISOLDE ISAC-II ISAC-I SPIRAL2 SPIRAL FAIR SIS RIBF RARF 2000 2005 2010 2015 NSCL HRIBF In Flight ISOL Fission+Gas Stopping Beam on target CARIBU@ATLAS RIF 2020 Exotic Nuclei Paradigm-Changing Discovery Potential Complexity – Simplicity Comprehensive Understanding of Atomic Nuclei Links to nano-science, high energy physics, and the cosmos Applications Jargon • Key to conference is communication • Biggest bottleneck to communication is jargon. • Examples (some may shock you): – Jlab: Partons, generalized parton distributions, the sea, quantitative relation of Q2 to size, Bjorken x… – RIA: island of inversion, yrast states, gamma vibrations, intruder states, K quantum number, B(E2) values, density functional theory… Thanks to many from whom I have stolen slides, especially Witek Have a great Workshop !!!