Text. References and Figures from: - Basdevant et al., Fundamentals in Nuclear Physics - Henley et al., Subatomic Physics

Transcription

1 Lecture 8 Experimental Nuclear Physics PHYS 741 Text heeger@wisc.edu References and Figures from: - Basdevant et al., Fundamentals in Nuclear Physics - Henley et al., Subatomic Physics 1

2 Review: Parity Violation - Signature of the Weak Force Scattering experiments with polarized n,p, e beams can tell us not only about the structure of nuclei and nucleons but also about the fundamental forces and interactions spins & parity parity violation weak mixing angle weak charge 4

3 Review: Discovery of Parity Violation in 1956 beta-decay of 60 Co nuclei C. S. Wu of Columbia University and Ernest Ambler, Raymond W. Hayward, Dale D. Hoppes, and Ralph P. Hudson. If parity were conserved in such interactions, then the intensity of the beta emission should be the same in either direction along the axis of spin. 5

4 CPT - Three important discrete symmetries C Symmetry - C operation changes particles to anti-particles in a system of interacting particles. - Charge (C) Violation is observed in weak interactions, but not in electromagnetic or strong interactions. - C violation occurs when the rate for a particle interaction is different if all the particles in the interaction are changed to anti-particles. C Violation was first demonstrated in 1957 by physicists at the University of Liverpool studying the decay of muons to electrons and antimuons to positrons and then analyzing the polarization of the electrons and positrons. It was found that muons decayed to left-handed electrons but not to right-handed electrons, and that anti-muons decayed to right-handed positrons but not to left-handed positrons. T Symmetry - T operation reverses the direction of time in that system. Combinations of these operations, such as CP and CPT, are also very important. CPT Combined symmetry CPT is believed to be conserved for all particle interactions. Consequences of CPT symmetry are that a particle and its anti-particle should have the same mass and lifetime. No violations of CPT have yet been observed. 6

5 CPT - Three important discrete symmetries CP was observed to be violated at a small level in the weak interactions of kaons (particles that contain a down-type quark and a strange-type quark) in 1964 by James Cronin and Val Fitch and collaborators, for which they won the Nobel Prize in physics in CP violation has also been observed in the weak interactions of particles involving bottom quarks. This is the main program for the BaBar experiment at SLAC. CP Violation CP violation, however, has been observed. CP violation is especially intriguing, since it is believed to be a necessary ingredient to explain the preponderance of matter over antimatter in the universe. When C and P Violation were first observed in 1956 and 1957, it was expected that when C and P operations were combined together (the CP operation), symmetry would still be preserved. Otherwise, CP violation would necessarily imply T violation in order to conserve CPT. Time (T) Violation has also been observed in the weak interactions of kaons by the CPLEAR experiment at CERN and the KTEV experiment at Fermilab. T Violation means that the rate for a particle interaction is different for the time-reversed process 7

6 Research News Neutron Charge Density The textbook version Derived Charge and Magnetic Moment Densities proton: most charge within < 0.8 fm neutron: positively charged core < 0.3fm surrounded by neg charge 0.3-2fm G. Miller et al., 2008 negative core at center of neutron due to fast moving down quarks negative down quark found to have higher momentum qd=-1/3 mostly found near center of neutron 8

7 Course Projects By October 5 Pick three topics of interest from the list (ranked by preference) or define your own topic for the research project and those to me. If more than one person is interested in a given subject, I will assign a topic based on your preferences. By October 17 Establish a reading list of at least three readable references on the subject that is finally assigned to you, and go over the reading list with me so we agree on what you will read and research for the project. By November 21 Prepare a conference-style presentation in PowerPoint, Keynote, PDF, or in some other electronic presentation format. Let me know if you do not have access to a computer to prepare the presentation. me the electronic file of your presentation so I can look it over. November 24 - December 3 Arrange a time to meet with me to go over the draft presentation, and then refine your presentation based on our individual discussions. December 5 (or some other day) Project presentations to the class. We will schedule an afternoon or evening with pizza to hear everyone s presentation. 9

8 Frontiers in Nuclear Science: The Long Range Plan Current Activities and Future Plan of US Nuclear Physics 10

9 Quarks, Particles, and Nuclei 11

10 Research Themes in Nuclear Physics Fundamental Symmetries and Neutrinos Nuclei and Nuclear Astrophysics Quantum Chromodynamics (QCD) 12

11 Fundamental Symmetries and Neutrinos 13

12 Karsten Heeger, Univ. of Wisconsin ANL, May 23, 2008

13 Neutrinos and Cosmology We see imprints of neutrino mass in the structure of todayʼs Universe very early universe big bang nucleosynthesis late time structure formation WMAP large-scale structure enhanced early ISW effect effect on structure formation Neutrinos that are more massive cause more clustering on large scales. Even small neutrino mass influences power spectrum of galaxy correlations Karsten Heeger, Univ. of Wisconsin ANL, May 23, 2008

14 Understanding Origin of Matter Are ν Majorana? Is CP? Leptogenesis (Fukugita, Yanagida, 1986) Out-of-equilibrium L-violating decays of heavy Majorana neutrinos leading to L asymmetry but leaving B unchanged. Anomalous processes change B L and L L but not B L -L L. Redistribute L asymmetry. L in Universe is mostly carried by 2 K neutrinos. Observable effect is baryon asymmetry. ν R neutrinos responsible for generation of lepton asymmetry may also be responsible for smallness of the observed neutrino mass through the see-saw mechanism Karsten Heeger, LBNL Harvard University, March 14, 2006

15 Birth of Neutrino Astrophysics 1938 Bethe & Critchfield p + p 2 H + e + + ν e 1947 Pontecorvo,1949 Alvarez propose neutrino detection through 37Cl + ν e 37 Ar + e - Light Element Fusion Reactions p + p 2 H + e + + ν e p + e - + p 2 H + ν e 99.75% 0.25% 2H + p 3 He + γ 85% ~15% ~10-5 % 3He + 3 He 4 He + 2p 3He + p 4 He + e + +ν e 3He + 4 He 7 Be + γ 1960ʼs Ray Davis builds chlorine detector. John Bahcall, generates first solar model calculations and ν flux predictions % 7Be + e - 7 Li + γ +ν e 7Li + p α + α 0.02% 7Be + p 8 B + γ 8B 8 Be* + e + + ν e to see into the interior of a star and thus verify directly the hypothesis of nuclear energy generation in stars... (Bahcall, 1964) Karsten Heeger, LBNL Harvard University, March 14, 2006

16 Cl-Ar Solar Neutrino Experiment at Homestake ν e + 37 Cl 37 Ar + e SSM only sensitive to ν e Karsten Heeger, LBNL Harvard University, March 14, 2006

17 The Solar Neutrino Problem and Its Resolution Too few ν e observed from the Sun. ν e ν e ν e ν e Even with all solar neutrino fluxes as free parameters, cannot reproduce the data. P MSM < 1.7% at 95% CL KMH, Robertson PRL 77:3270 (1996) Neutral Current (NC) Elastic Scattering (ES) Charged Current (CC) CC Neutral-Current shape Elastic Scattering Results from Charged-Current SNO, 2002 constrained Neutrino Signal (SSM/BP00) SSM 5.3 σ Karsten Heeger, Univ. of Wisconsin ANL, May 23, CC shape unconstrained ν e + ν µ +ν τ Total Neutrino flux ν e (ν µ +ν τ ) ν e Electron Neutrino flux Neutrinos have mass and change flavor

18 Neutrino Mass and Particle Nature ν = ν? normal inverted quasi-degenerate Δm atm 2 m ν > 0.04 ev What is the absolute mass scale? What is the mass hierarchy? Are neutrinos their own antiparticles? Karsten Heeger, Univ. of Wisconsin ANL, May 23, 2008

19 Neutrinoless Double Beta Decay: 0νββ 2ν mode: conventional 2 nd order process in nuclear physics Γ 2ν = G 2ν M 2ν 2 G are phase space factors 0ν mode: hypothetical process only if M ν 0 AND ν = ν Γ 0ν = G 0ν M 0ν 2 m ββ 2 G 0ν ~ Q 5 0νββ would imply - lepton number non-conservation - Majorana nature of neutrinos Karsten Heeger, Univ. of Wisconsin ANL, May 23, νββ may allow us to determine - absolute neutrino mass scale - neutrino mass hierarchy

20 Neutrinoless Double Beta Decay: 0νββ 22

21 Neutrinoless Double Beta Decay: 0νββ Γ 0ν = G 0ν M 0ν 2 m ββ 2 23

22 Direct Neutrino Mass Measurements 24

23 Probing New Physics in Neutrino Mass Why is the neutrino mass so small? PDG 2000 PDG SNO + SK (ν 3 ) < ν 1 < ν 2 < (ν 3 ) ν e ν µ ν τ What are the new symmetries? Neutrinos are demonstrated experimental window on physics beyond the Standard Model! Karsten Heeger, Univ. of Wisconsin ANL, May 23, 2008

24 Going Underground for Precision Science 26

25 Deep Underground Science and Engineering Laboratory 27

26 Electric Dipole Moment Searches 28

27 Electric Dipole Moment Searches P reflection reverses the EDM but not the spin angular momentum In Fig. (b), reversing T reverses the spin angular momentum but not the EDM. 29

28 Electric Dipole Moment Searches 30

29 Electroweak Interactions of Leptons and Quarks Parity Violating Electron Scattering Scale dependence of the weak mixing angle in the Standard Model 31

30 Muon g-2 measuring the anomalous magnetic moment of the muon 32

31 Neutrino Probes of Supernovae 33

32 Geoneutrinos 34

33 Nuclei and Nuclear Astrophysics 35

34 Nuclear Reactions in Stars and Stellar Explosions 36

35 Shell Structure of Lighter Nuclei 37

36 Neutron Stars 38

37 Neutron Stars 39

38 Neutron Star Crust 40

39 QCD From the Structure of Hadrons to the Phases of Nuclear Matter 41

40 Spatial Structure of Protons and Neutrons combined results of experiments neutron proton Miller

41 What is the internal landscape of the nucleons? measurements of gluon spin preferences by using high-energy proton collisions at RHIC polarized proton and preferred spin orientations of the u,d,s quarks fractional polarization of down quark quarkʼs momentum fraction fractional polarization of d is negative. will it change sign? 43

42 Number Density of Gluons and Quarks inside Proton curves are from fits to high-energy scattering data partons ~ quarks and gluons 44

43 Quarkʼs Effective Mass lattice QCD calculations bulk of the constituent mass of a light quark comes from a cloud of gluons quark appears massless at high energies quark mass depends on its momentum 45

44 Lattice QCD Calculation lattice QCD approach of calculating nucleon properties charge radius of an isovector nucleon (proton - neutron) for a variety of pion masses 46

45 Phase Transition in QCD Matter deconfinement phase transition 47

46 Phases of QCD 48

47 Nuclear Physics and Other Fields 49

48 Connections to Other Fields Particle Physics 50

49 Connections to Other Fields Astrophysics, Hydrodynamics 51

50 Connections to Other Fields Plasma Physics 52

51 Applications of Nuclear Science 53

52 Employment of Nuclear Science PhDs what are the other 60% of nuclear scientists doing? 54

53 Applications of Nuclear Science Luis Alvarez From studying pyramids to cargo screening 55

54 Applications of Nuclear Science Muon Tomography for Cargo Screening 56

55 Applications of Nuclear Science MRIScreen ultra-low field nuclear magnetic resonance imaging uses the response of different liquids to magnetic resonance imaging to distinguish between good and bad liquids 57

56 Applications of Nuclear Science Magnetic resonance imaging of 128 Xe 58

57 Applications of Nuclear Science Proton Radiograph 59

58 60