Hot Topics in Physics. OLLI lectures Fall 2016 Horst D Wahl lecture 5, 8 Nov 2016

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1 Hot Topics in Physics OLLI lectures Fall 2016 Horst D Wahl (hwahl@fsu.edu) lecture 5, 8 Nov

2 Recap Neutrinos (cont d) Outline of 5 th class More than one neutrino Weak interactions and neutrino Neutrino properties Solar neutrinos Interlude: some nuclear physics Nuclear Fusion Nuclear fusion processes in stars Neutrinos overview Interlude: about stars 2

3 Cosmology: Recap Present Cosmology paradigm: CDM theory of Big Bang explains/predicts all observations main findings: o Big Bang Gy ago o Universe s expansion appears to be accelerating Only 4.6% of Universe is standard matter, rest is Dark Matter (26.9%) and Dark Energy (68.3%) 3

Contents of the universe Planck's high-precision cosmic microwave background map has allowed scientists to extract the most refined values yet of the Universe's ingredients.

4 Contents of the universe Planck's high-precision cosmic microwave background map has allowed scientists to extract the most refined values yet of the Universe's ingredients. Normal matter that makes up stars and galaxies contributes just 4.9% of the Universe's mass/energy inventory. Dark matter, which is detected indirectly by its gravitational influence on nearby matter, occupies 26.8%, while dark energy, a mysterious force thought to be responsible for accelerating the expansion of the Universe, accounts for 68.3%. ( ) The 'before Planck' figure is based on the WMAP 9-year data release presented by Hinshaw et al., (2012). 4

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8 Summary Cosmology now a mature quantitative science All observations explained by CDM theory of Big Bang detailed studies of the CMB power spectrum and better distance calibration using SNe as standard candles leads to quantitative information about age of the universe and its composition Big Bang Gy ago Only 4.6% of Universe is standard matter, rest is Dark Matter (26.9%) and Dark Energy (68.3%) 8

9 And Now: Neutrinos!!! 9

are different from the neutrinos emitted in

10 More than one neutrino! Lederman, Schwartz, Steinberger: Experiment at BNL (Brookhaven Nat. Lab.) Use neutrinos from pion decay Show that they are different from the neutrinos emitted in beta decay Nobel Prize 1988 Shielding: 2000 tons of steel from scrapped warships (armor) 10

A 3 rd Lepton -- SPEAR (e + e - storage ring at SLAC), 1975 Find evidence for reaction e e e X where X = at least 2 undetected particles Interpretation (Martin Perl) e e e 4 3 rd lepton ( ί

11 A 3 rd Lepton -- SPEAR (e + e - storage ring at SLAC), 1975 Find evidence for reaction e e e X where X = at least 2 undetected particles Interpretation (Martin Perl) e e e 4 3 rd lepton ( ί the 3 rd ) Verified by experiment at DESY (Hamburg) Nobel Prize 1995 for M. Perl (shared with Frederick Reines) 11

12 DONUT (direct observation of ) at Fermilab (1997) Produce tau-neutrinos from decay of charmed particles Observation of events of type p Observe decay products of in detector 3 rd neutrino -- X 12

13 The Number of light neutrinos Discovery of Z o (1983 by UA1, UA2 at CERN) From width of Z decay, get upper limit on number of light neutrinos: N < 3.8 (1987) ( light means mass of < m Z /2 ~ 45 GeV Studies of Z at LEP (2003): measurement of cross section vs beam energy allows determination of number of light neutrinos (Z o can decay to a neutrino and antineutrino) 13

14 Weak Interactions and the Neutrino Neutrinos have weak interaction: No electric charge No color charge Weakness of weak interactions: Mediated by W, Z o W and Z massive m w = 80 GeV m z = 91 GeV for E << m w, m z, Coupling ~ 1/m W 2 Uncertainty relation E t 2 Beta decay of neutron: I can borrow an elephant, provided I give it back on time (soon)! Interactions can only occur over very small distances Result: small cross section, or weak strength of interaction 14

Lepton number: Total number of leptons conserved Leptons minus antileptons Example: Electrons always produced with antineutrinos Neutrino Properties Lepton flavor

15 Lepton number: Total number of leptons conserved Leptons minus antileptons Example: Electrons always produced with antineutrinos Neutrino Properties Lepton flavor number (e,, ) : Total number of leptons in each generation conserved Only one flavor allowed at a vertex Spin: Neutrinos are fermions: spin ½ Neutrino-electron scattering 15

Helicity and Mass Helicity: projection of spin along momentum axis For spin ½ particles, two states +½, -½ Right or Left handed Observation: All leptons in weak interactions are left handed.

16 Helicity and Mass Helicity: projection of spin along momentum axis For spin ½ particles, two states +½, -½ Right or Left handed Observation: All leptons in weak interactions are left handed. All anti leptons in weak interactions are right handed But helicity is not a Lorentz invariant: I can transform to a frame where the particle is moving in the opposite direction One solution: Massless neutrinos Move at c in all frames Helicity becomes a good quantum number Chirality (handedness) is intrinsic property Same as helicity for massless particles 16

17 Neutrino in the (original) Standard Model weak interaction mediated by W and Z bosons Couple to left handed fermions, right handed antifermions Particles of the Standard Model Neutrinos have exactly zero mass One neutrino flavor per lepton Higgs, which is responsible for mass, does not interact with neutrinos Neutrinos and antineutrinos are distinct (different chirality) 17

nucleosynthesis Fission in reactors High energy

18 Sources of Neutrinos Nuclear reactions Fusion in the sun (and other stars) SuperNovae Big bang nucleosynthesis Fission in reactors High energy collisions Particle colliders Cosmic ray showers 18

19 Solar Neutrinos Neutrinos from Sun Interlude: some nuclear physics Neutrino overview Interlude: about stars Back to solar neutrinos 19

20 Neutrinos from the Sun Helium Reactionchains Energy 26.7 MeV Solar radiation: 98 % light 2 % neutrinos At Earth 66 billion neutrinos/cm2 sec Hans Bethe ( , Nobel prize 1967) Thermonuclear reaction chains (1938) 20

21 ne 21

22 Interlude: some nuclear physics Structure of nucleus A,N,Z Atomic mass unit Nucleons Nuclear masses, isotopes Nuclear masses, binding energy Binding energy vs A Nuclear energy Fission, fusion 22

23 About Units Energy - electron-volt 1 electron-volt = kinetic energy of an electron when moving through potential difference of 1 Volt; o 1 ev = Joules o 1 kw hr = Joules = ev o 1 MeV = 106 ev, 1 GeV= 109 ev, 1 TeV = 1012 ev mass - ev/c2 o o o o 1 ev/c2 = kg electron mass = MeV/c2 proton mass = 938 MeV/c2 = GeV/ c2 neutron mass = MeV/c2 momentum - ev/c: o 1 ev/c = kg m/s o momentum of baseball at 80 mi/hr 5.29 kgm/s ev/c Distance o 1 femtometer ( Fermi ) = m 23

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25 Structure of nucleus size (Rutherford 1910, Hofstadter 1950s): R = r0 A1/3, r0 = 1.2 x m = 1.2 fm; i.e nucleons / fm3 generally roughy spherical shape, almost uniform density; (but can be highly deformed in high spin excited states) made up of protons and neutrons protons and neutron -- nucleons ; are fermions (spin ½), have magnetic moment nucleons confined to small region ( potential well ) occupy discrete energy levels two distinct (but similar) sets of energy levels, one for protons, one for neutrons proton energy levels slightly higher than those of neutrons (electrostatic repulsion) spin ½ Pauli principle only two identical nucleons per energy level 25

increases with Z nomenclature: ZAXN or AXN or A X or X-A http://www.nndc.bnl.

26 A, N, Z for natural nuclei: Z range 1 (hydrogen) to 92 (Uranium) A range from 1 ((hydrogen) to 238 (Uranium) N = neutron number = A-Z N Z = neutron excess ; increases with Z nomenclature: ZAXN or AXN or A X or X-A ml 26

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29 Atomic mass unit atomic number Z Number of protons in nucleus Mass Number A Number of protons and neutrons in nucleus Atomic mass unit is defined in terms of the mass of 126C, with A = 12, Z = 6: 1 amu = (mass of 126C atom)/12 1 amu = 1.66 x 10-27kg 1 amu = MeV/c2 29

30 Properties of Nucleons Proton Charge = 1 elementary charge e = x C Mass = x kg = MeV/c2 = u = 1836 me spin ½, magnetic moment 2.79 eħ/2mp Neutron Charge = 0 Mass = x kg = MeV/c2 = u = 1839 me spin ½, magnetic moment -1.9 eħ/2mn 30

31 Nuclear masses, isotopes Nuclear masses measured, e.g. by mass spectrography masses expressed in atomic mass units (amu), energy units MeV/c2 all nuclei of certain element contain same number of protons, but may contain different number of neutrons examples: deuterium, heavy hydrogen 2D or 2H; heavy water = D2O (0.015% of natural water) U- 235 (0.7% of natural U), U-238 (99.3% of natural U), 31

32 Nuclear energy levels: example Estimate the lowest possible energy of a neutron contained in a typical nucleus of radius m. E = p2/2m = (cp)2/2mc2 x p = h/2 x (cp) = hc/2 (cp) = hc/(2 x) = hc/(2 r) (cp) = 6.63x10-34 Js 3x108 m/s / (2 1.33x10-15 m) (cp) = 2.38x10-11 J = MeV E = p2/2m = (cp)2/2mc2 = (148.6 MeV)2/(2*940 MeV) = 11.7 MeV 32

33 Nuclear Masses, binding energy Mass of Nucleus Z(mp) + N(mn) mass defect m = difference between mass of constituents and mass of nucleus and energy defect = binding energy EB EB = mc2 binding energy = amount of energy that must be invested to break up nucleus into its constituents binding energy per nucleon = EB /A 33

34 Nuclear Binding Energy Nuclear binding energy = difference between the energy (or mass) of its constituent neutrons and protons, and the energy (or mass) of the nucleus = the energy needed to break the nucleus apart Average binding energy per nucleon = total binding energy divided by the number of nucleons (A). Example: Fe-56 1 amu = m(proton) m(neutron) A= Z= N= Mass (amu) Ebinding (MeV) EB/A(MeV) MeV

35 N-Z and binding energy vs A small nuclei (A<10): All nucleons are within range of strong force exerted by all other nucleons; add another nucleon enhance overall cohesive force EB rises sharply with increase in A medium size nuclei (10 < A < 60) nucleons on one side are at edge of nucl. force range from nucleons on other side each add l nucleon gives diminishing return in terms of binding energy slow rise of EB /A heavy nuclei (A>60) adding more nucleons does not increase overall cohesion due to nuclear attraction Repulsive electrostatic forces (infinite range!) begin to have stronger effect N-Z must be bigger for heavy nuclei (neutrons provide attraction without electrostatic repulsion heaviest stable nucleus: 209Bi all nuclei heavier than 209Bi are unstable (radioactive) 35

36 EB/A vs A 36

37 Binding energy per nucleon 37

38 Nuclear energy very heavy nuclei: energy released if break up into two medium sized nuclei fission light nuclei: energy released if two light nuclei combine -- fuse into a heavier nucleus fusion 38

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41 CPEP contemporary education project ics.org/fusion_chart. html# 41

42 Neutrinos from the Sun Helium Reactionchains Energy 26.7 MeV Solar radiation: 98 % light 2 % neutrinos At Earth 66 billion neutrinos/cm2 sec Hans Bethe ( , Nobel prize 1967) Thermonuclear reaction chains (1938) 42

43 Bethe s Classic Paper on Nuclear Reactions in Stars No neutrinos from nuclear reactions in

44 Fusion reactions in stars Fuse light nuclei to heavier ones, e.g.: p + p He, He + He 8Be, He + 8Be 12C 12C + 12C 20Ne + He 12C + 12C 16O + 2 He. positively charged nuclei need to overcome Coulomb barrier to get close enough to each other so that (short range) strong interaction can take over and bind them Need high temperatures to have high enough kinetic energies 44

45 Hydrogen Burning Proton Proton Reactions to form He Main energy source in stars for most of their lives + Energy! (26.7 MeV) 45

46 Life of a 20 Solar Mass Super-Giant Hydrogen fusion ~ 10 million years Helium fusion ~ 1 million years Carbon fusion ~ 300 years Oxygen fusion ~ 9 months Silicon fusion ~ 2 days 46

47 Carbon fusion 7.65 MeV above 12C ground state 47

48 A Nearby Super-Giant 48

49 Facts about Neutrinos Neutrinos are only weakly interacting 40 billion neutrinos continuously hit every cm2 on earth from the Sun (24hrs/day) Interaction length is ~1 light-year of steel 1 out of 100 billion interact going through the Earth 49

50 Neutrino production from Nuclear Reactions in the Sun Fusion of H to He is the basic energy source of the Sun: 4p 4He + 2e+ + 2ne MeV G. Sullivan Quarknet, July

51 Neutrino puzzles Solar Neutrinos Problem 3 experiments showed a deficit of solar neutrinos. o Going back ~30 years About 1/3 to ½ of the expected number were observed results could not be reconciled with the standard solar model Atmospheric Neutrino Anomaly IMB and Kamiokande saw less than expected ratio of nm/ ne One Proposed Explanation was: Neutrino Oscillations Solar neutrinos might be ne -> nm Atmospheric neutrinos might be nm -> nt Confirmed by Kamiokande and Sudbury experiments 51

52 Super Kamiokande: Solar Neutrinos Solar neutrino Electron 52

53 Solar Neutrino puzzle Missing neutrinos from the Sun Now explained as due to neutrino oscillations three neutrino types: electron neutrino e, muon neutrino, tau neutrino can change their identity oscillate if masses are not all the same Oscillation period depends on (mass difference)2 only possible if not all neutrinos are massless

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55 pp chain Net result is: 4p CNO cycle 4He + 2e+ + 2ne MeV 55

Nuclear and Particle Physics. 3 lectures: Nuclear Physics Particle Physics 1 Particle Physics 2

Nuclear and Particle Physics. 3 lectures: Nuclear Physics Particle Physics 1 Particle Physics 2 Nuclear and Particle Physics 3 lectures: Nuclear Physics Particle Physics 1 Particle Physics 2 1 Nuclear Physics Topics Composition of Nucleus features of nuclei Nuclear Models nuclear energy Fission Fusion